acetaminophen/diphenhydramine/phenylephrine (OTC)

Brand and Other Names:Benadryl Allergy & Cold, Sudafed PE Severe Cold, more...Delsym Cough + Cold Night Time, Children's Delsym Cough + Cold Night Time, Benadryl Severe Allergy & Sinus Headache, Children's Tylenol Plus Cold & Allergy, Benadryl Allergy & Sinus Headache, Robitussin Peak Cold Nighttime Multi-Symptom Cold, Theraflu Nighttime Severe Cold & Cough, Theraflu Warming Relief Flu & Sore Throat, Theraflu Warming Relief Nighttime Severe Cold & Cough, Tylenol Allergy Multi-Symptom Nighttime
  • Print
Sections

Dosing & Uses

AdultPediatric

Dosage Forms & Strengths

acetaminophen/diphenhydramine/phenylephrine

caplet

  • 325mg/25mg/5mg
  • 325mg/12.5mg/5mg
  • 650mg/25mg/10mg

liquid

  • (160mg/6.25mg/2.5mg)/5mL
  • (160mg/12.5mg/2.5mg)/5mL

syrup

  • 325mg/12.5mg/5mg

packet

  • 650mg/25mg/10mg

Rhinorrhea, Nasal Congestion, Headache

Benadryl Allergy & Cold: 2 caplet PO q4hr; not to exceed 12 capsules/day

Benadryl Allergy & Sinus Headache: 2 caplet PO q4hr; not to exceed 12 capsules/day

Benadryl Severe Allergy & Sinus Headache: 2 caplet PO q4hr; not to exceed 12 capsules/day

Robitussin Peak Cold Nighttime Multi-Symptom Cold: 20 mL PO q4hr; not to exceed 6 doses/24 hr

Sudafed PE Nighttime Cold: 2 caplet PO q4hr; not to exceed 12 caplet/day

Sudafed PE Severe Cold: 2 caplet PO q4hr; not to exceed 12 caplet/day

Theraflu Nighttime Severe Cold & Cough; 1 packet dissolved in 8 oz of water PO q4hr; not to exceed 6 packet/day

Theraflu Warming Relief Nighttime Severe Cold & Cough: 2 tablespoonfuls (30 mL) PO q4hr; not to exceed 6 doses/day

Tylenol Allergy Multi-Symptom Nighttime: 2 caplet PO q4hr; not to exceed 12 caplet/day

Dosage Forms & Strengths

acetaminophen/diphenhydramine/phenylephrine

caplet

  • 325mg/25mg/5mg
  • 325mg/12.5mg/5mg
  • 650mg/25mg/10mg

liquid

  • (160mg/6.25mg/2.5mg)/5mL
  • (160mg/12.5mg/2.5mg)/5mL

syrup

  • 325mg/12.5mg/5mg

packet

  • 650mg/25mg/10mg

Rhinorrhea, Nasal Congestion, Headache

Benadryl Allergy & Cold

  • <6 years old: Ask a pediatrician
  • 6-12 years: 1 caplet PO q4hr; not to exceed 5 capsules/day
  • >12 years: 2 caplet PO q4hr; not to exceed 12 capsules/day

Benadryl Allergy & Sinus Headache

  • < 6 years: Ask a pediatrician
  • 6-12 years: 1 capsule PO q4hr; maximum 5 capsules/day
  • >12 years: 2 capsules PO q4hr; not to exceed 12 capsules/day

Benadryl Severe Allergy & Sinus Headache

  • < 6 years old: Ask a pediatrician
  • 6-12 years old: 1 capsule PO q4hr; maximum 5 capsules/day
  • >12 years old: 2 capsules PO q4hr; not to exceed 12 capsules/day

Children's Tylenol Plus Cold & Allergy

  • <4 years old: Do not use
  • 4-6 years old: Ask a pediatrician
  • 6-12 years old: 10 mL PO q4hr; not to exceed 5 doses/day

Robitussin Peak Cold Nighttime Multi-Symptom Cold

  • <12 years: Do not use
  • 12 years or older: 20 mL PO q4hr; not to exceed 6 doses/24 hr

Sudafed PE Nighttime Cold

  • <12 years old: Ask a pediatrician
  • >12 years old: 2 caplets PO q4hr; not to exceed 12 caplets/day

Sudafed PE Severe Cold

  • <6 years: Ask a pediatrician
  • 6-12 years: 1 caplets PO q4hr; not to exceed 5 caplets/day
  • >12 years: 2 caplets PO q4hr; not to exceed 12 caplets/day

Theraflu Nighttime Severe Cold & Cough

  • <12 years: Ask a pediatrician
  • >12 years: 1 packet dissolved in 8 oz of water PO q4hr; not to exceed 6 packet/day

Theraflu Warming Relief Flu & Sore Throat

  • <12 years: Ask a pediatrician
  • >12 years: 2 tablespoonfuls (30 mL) PO q4hr; not to exceed 6 doses/day

Theraflu Warming Relief Nighttime Severe Cold & Cough

  • <12 years: Ask a pediatrician
  • >12 years: 2 tablespoonfuls (30 mL) PO q4hr; not to exceed 6 doses/day

Tylenol Allergy Multi-Symptom Nighttime

  • <12 years: Do not use
  • >12 years: 2 caplets PO q4hr; not to exceed 12 caplets/day
Next:

Interactions

Interaction Checker

and acetaminophen/diphenhydramine/phenylephrine

No Results

     activity indicator 
    No Interactions Found
    Interactions Found

    Contraindicated

      Serious - Use Alternative

        Significant - Monitor Closely

          Minor

            All Interactions Sort By:
             activity indicator 

            Contraindicated (2)

            • eliglustat

              diphenhydramine increases levels of eliglustat by affecting hepatic enzyme CYP2D6 metabolism. Contraindicated. If coadministered with strong or moderate CYP2D6 inhibitors, reduce eliglustat dose from 84 mg BID to 84 mg once daily in extensive and intermediate metabolizers; eliglustat is contraindiated if strong or moderate CYP2D6 inhibitors are given concomitantly with strong or moderate CYP3A inhibitors.

            • iobenguane I 123

              phenylephrine decreases effects of iobenguane I 123 by receptor binding competition. Contraindicated. If clinically appropriate, discontinue drugs that compete for NE receptor sites for at least 5 half-lives; may cause false-negative imaging results.

            Serious - Use Alternative (33)

            • amitriptyline

              amitriptyline, phenylephrine. Other (see comment). Avoid or Use Alternate Drug. Comment: Tricyclic antidepressants increase or decrease effects of sympathomimetics, by blocking reuptake of NE, or blocking uptake of indirect sympathomimetics into the adrenergic neuron.

            • amoxapine

              amoxapine, phenylephrine. Other (see comment). Avoid or Use Alternate Drug. Comment: Tricyclic antidepressants increase or decrease effects of sympathomimetics, by blocking reuptake of NE, or blocking uptake of indirect sympathomimetics into the adrenergic neuron.

            • cabergoline

              cabergoline, phenylephrine. Mechanism: pharmacodynamic synergism. Contraindicated. Additive vasospasm; risk of hypertension.

            • calcium/magnesium/potassium/sodium oxybates

              diphenhydramine, calcium/magnesium/potassium/sodium oxybates. Either increases effects of the other by pharmacodynamic synergism. Avoid or Use Alternate Drug. Profound sedation, respiratory depression, coma, and death may result if coadministered. Reserve concomitant prescribing of these drugs in patients for whom other treatment options are inadequate. Limit dosages and durations to the minimum required. Monitor closely for signs of respiratory depression and sedation.

            • clomipramine

              clomipramine, phenylephrine. Other (see comment). Avoid or Use Alternate Drug. Comment: Tricyclic antidepressants increase or decrease effects of sympathomimetics, by blocking reuptake of NE, or blocking uptake of indirect sympathomimetics into the adrenergic neuron.

            • desflurane

              desflurane increases toxicity of phenylephrine by Mechanism: unknown. Avoid or Use Alternate Drug. Risk of V tach, HTN.

              desflurane increases levels of phenylephrine by decreasing metabolism. Contraindicated.

            • desipramine

              desipramine, phenylephrine. Other (see comment). Avoid or Use Alternate Drug. Comment: Tricyclic antidepressants increase or decrease effects of sympathomimetics, by blocking reuptake of NE, or blocking uptake of indirect sympathomimetics into the adrenergic neuron.

            • dihydroergotamine

              dihydroergotamine, phenylephrine. Mechanism: pharmacodynamic synergism. Contraindicated. Additive vasospasm; risk of hypertension.

            • dihydroergotamine intranasal

              dihydroergotamine intranasal, phenylephrine. Mechanism: pharmacodynamic synergism. Contraindicated. Additive vasospasm; risk of hypertension.

            • doxapram

              doxapram increases effects of phenylephrine by pharmacodynamic synergism. Avoid or Use Alternate Drug. Additive pressor effect.

            • doxepin

              doxepin, phenylephrine. Other (see comment). Avoid or Use Alternate Drug. Comment: Tricyclic antidepressants increase or decrease effects of sympathomimetics, by blocking reuptake of NE, or blocking uptake of indirect sympathomimetics into the adrenergic neuron.

            • eluxadoline

              diphenhydramine, eluxadoline. Either increases effects of the other by pharmacodynamic synergism. Avoid or Use Alternate Drug. Avoid coadministration with other drugs that cause constipation. Increases risk for constipation related serious adverse reactions.

            • ergoloid mesylates

              ergoloid mesylates, phenylephrine. Mechanism: pharmacodynamic synergism. Contraindicated. Additive vasospasm; risk of hypertension.

            • ergotamine

              ergotamine, phenylephrine. Mechanism: pharmacodynamic synergism. Contraindicated. Additive vasospasm; risk of hypertension.

            • ether

              ether increases toxicity of phenylephrine by Mechanism: unknown. Avoid or Use Alternate Drug. Risk of V tach, HTN.

            • etomidate

              etomidate increases levels of phenylephrine by decreasing metabolism. Contraindicated.

            • imipramine

              imipramine, phenylephrine. Other (see comment). Avoid or Use Alternate Drug. Comment: Tricyclic antidepressants increase or decrease effects of sympathomimetics, by blocking reuptake of NE, or blocking uptake of indirect sympathomimetics into the adrenergic neuron.

            • isocarboxazid

              isocarboxazid increases effects of diphenhydramine by Other (see comment). Avoid or Use Alternate Drug. Comment: Isocarboxazid should not be administered in combination with antihistamines because of potential additive CNS depressant effects. MAO inhibitors also prolong and intensify anticholinergic effects of antihistamines. .

            • isoflurane

              isoflurane increases toxicity of phenylephrine by Mechanism: unknown. Avoid or Use Alternate Drug. Risk of V tach, HTN.

            • lofepramine

              lofepramine, phenylephrine. Other (see comment). Avoid or Use Alternate Drug. Comment: Tricyclic antidepressants increase or decrease effects of sympathomimetics, by blocking reuptake of NE, or blocking uptake of indirect sympathomimetics into the adrenergic neuron.

            • lonafarnib

              acetaminophen will increase the level or effect of lonafarnib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. If coadministration of lonafarnib (a sensitive CYP3A substrate) with weak CYP3A inhibitors is unavoidable, reduce to, or continue lonafarnib at starting dose. Closely monitor for arrhythmias and events (eg, syncope, heart palpitations) since lonafarnib effect on QT interval is unknown.

            • maprotiline

              maprotiline, phenylephrine. Other (see comment). Avoid or Use Alternate Drug. Comment: Tricyclic antidepressants increase or decrease effects of sympathomimetics, by blocking reuptake of NE, or blocking uptake of indirect sympathomimetics into the adrenergic neuron.

            • mefloquine

              mefloquine increases toxicity of diphenhydramine by QTc interval. Avoid or Use Alternate Drug. Mefloquine may enhance the QTc prolonging effect of high risk QTc prolonging agents.

            • methoxyflurane

              methoxyflurane increases toxicity of phenylephrine by Mechanism: unknown. Avoid or Use Alternate Drug. Risk of V tach, HTN.

            • methylergonovine

              methylergonovine, phenylephrine. Mechanism: pharmacodynamic synergism. Contraindicated. Additive vasospasm; risk of hypertension.

            • metoclopramide intranasal

              diphenhydramine, metoclopramide intranasal. Either increases effects of the other by Other (see comment). Avoid or Use Alternate Drug. Comment: Avoid use of metoclopramide intranasal or interacting drug, depending on importance of drug to patient.

            • nortriptyline

              nortriptyline, phenylephrine. Other (see comment). Avoid or Use Alternate Drug. Comment: Tricyclic antidepressants increase or decrease effects of sympathomimetics, by blocking reuptake of NE, or blocking uptake of indirect sympathomimetics into the adrenergic neuron.

            • olopatadine intranasal

              diphenhydramine and olopatadine intranasal both increase sedation. Avoid or Use Alternate Drug. Coadministration increases risk of CNS depression, which can lead to additive impairment of psychomotor performance and cause daytime impairment.

            • pexidartinib

              acetaminophen and pexidartinib both increase Other (see comment). Avoid or Use Alternate Drug. Pexidartinib can cause hepatotoxicity. Avoid coadministration of pexidartinib with other products know to cause hepatoxicity.

            • pitolisant

              diphenhydramine decreases effects of pitolisant by Other (see comment). Avoid or Use Alternate Drug. Comment: Pitolisant increases histamine levels in the brain; therefore, H1 receptor antagonists that cross the blood-brain barrier may reduce the efficacy of pitolisant.

            • pramlintide

              pramlintide, diphenhydramine. Either increases effects of the other by pharmacodynamic synergism. Contraindicated. Synergistic inhibition of GI motility.

            • pretomanid

              acetaminophen, pretomanid. Either increases toxicity of the other by Other (see comment). Avoid or Use Alternate Drug. Comment: Pretomanid regimen associated with hepatotoxicity. Avoid alcohol and hepatotoxic agents, including herbal supplements and drugs other than bedaquiline and linezolid.

            • propofol

              propofol increases levels of phenylephrine by decreasing metabolism. Contraindicated.

            Monitor Closely (344)

            • aclidinium

              diphenhydramine and aclidinium both decrease cholinergic effects/transmission. Use Caution/Monitor.

            • albuterol

              albuterol and phenylephrine both increase sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Use Caution/Monitor.

              diphenhydramine increases and albuterol decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              albuterol and phenylephrine both decrease sedation. Use Caution/Monitor.

            • alfentanil

              alfentanil increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine and alfentanil both increase sedation. Use Caution/Monitor.

            • alprazolam

              alprazolam increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine and alprazolam both increase sedation. Use Caution/Monitor.

            • amantadine

              diphenhydramine, amantadine. Mechanism: pharmacodynamic synergism. Use Caution/Monitor. Potential for increased anticholinergic adverse effects.

            • amitriptyline

              amitriptyline increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • amifampridine

              diphenhydramine increases toxicity of amifampridine by Other (see comment). Modify Therapy/Monitor Closely. Comment: Amifampridine can cause seizures. Coadministration with drugs that lower seizure threshold may increase this risk.

            • amitriptyline

              diphenhydramine and amitriptyline both decrease cholinergic effects/transmission. Modify Therapy/Monitor Closely.

              diphenhydramine and amitriptyline both increase sedation. Use Caution/Monitor.

            • amobarbital

              amobarbital increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine and amobarbital both increase sedation. Use Caution/Monitor.

            • amoxapine

              amoxapine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine and amoxapine both decrease cholinergic effects/transmission. Use Caution/Monitor.

              diphenhydramine and amoxapine both increase sedation. Use Caution/Monitor.

            • anticholinergic/sedative combos

              anticholinergic/sedative combos and diphenhydramine both decrease cholinergic effects/transmission. Use Caution/Monitor.

            • apalutamide

              apalutamide will decrease the level or effect of acetaminophen by increasing elimination. Use Caution/Monitor. Apalutamide induces UGT and may decrease systemic exposure of drugs that are UGT substrates.

            • arformoterol

              arformoterol and phenylephrine both decrease sedation. Use Caution/Monitor.

              arformoterol and phenylephrine both increase sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Use Caution/Monitor.

            • apomorphine

              diphenhydramine and apomorphine both increase sedation. Use Caution/Monitor.

            • arformoterol

              diphenhydramine increases and arformoterol decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • aripiprazole

              aripiprazole increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              aripiprazole increases effects of diphenhydramine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia.

              diphenhydramine decreases levels of aripiprazole by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.

              diphenhydramine and aripiprazole both increase sedation. Use Caution/Monitor.

              diphenhydramine decreases levels of aripiprazole by pharmacodynamic antagonism. Use Caution/Monitor.

            • armodafinil

              armodafinil and phenylephrine both decrease sedation. Use Caution/Monitor.

              diphenhydramine increases and armodafinil decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • atogepant

              acetaminophen will increase the level or effect of atogepant by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • atomoxetine

              atomoxetine, phenylephrine. Other (see comment). Use Caution/Monitor. Comment: Due to the potential for increases in blood pressure and heart rate, atomoxetine should be used cautiously with vasopressors such as phenylephrine.

              diphenhydramine will increase the level or effect of atomoxetine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

            • atracurium

              atracurium and diphenhydramine both decrease cholinergic effects/transmission. Use Caution/Monitor.

            • avapritinib

              acetaminophen will increase the level or effect of avapritinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • axitinib

              acetaminophen increases levels of axitinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • azelastine

              azelastine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • atropine

              atropine and diphenhydramine both decrease cholinergic effects/transmission. Use Caution/Monitor.

            • atropine IV/IM

              atropine IV/IM and diphenhydramine both decrease cholinergic effects/transmission. Use Caution/Monitor.

            • azelastine

              azelastine and diphenhydramine both increase sedation. Use Caution/Monitor.

            • baclofen

              diphenhydramine and baclofen both increase sedation. Use Caution/Monitor.

            • belladonna alkaloids

              belladonna alkaloids and diphenhydramine both decrease cholinergic effects/transmission. Use Caution/Monitor.

            • belladonna and opium

              belladonna and opium increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine and belladonna and opium both decrease cholinergic effects/transmission. Use Caution/Monitor.

              diphenhydramine and belladonna and opium both increase sedation. Use Caution/Monitor.

            • benperidol

              benperidol increases effects of diphenhydramine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia.

              diphenhydramine decreases levels of benperidol by pharmacodynamic antagonism. Use Caution/Monitor.

              benperidol increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine and benperidol both increase sedation. Use Caution/Monitor.

              diphenhydramine decreases levels of benperidol by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.

            • benzhydrocodone/acetaminophen

              diphenhydramine will increase the level or effect of benzhydrocodone/acetaminophen by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Hydromorphone (<3% of the circulating parent hydrocodone [benzhydrocodone is prodrug of hydrocodone]) is mainly formed by CYP2D6 mediated O-demethylation of hydrocodone. Hydromorphone may contribute to the total analgesic effect of hydrocodone.

            • benzphetamine

              benzphetamine and phenylephrine both decrease sedation. Use Caution/Monitor.

              benzphetamine and phenylephrine both increase sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Use Caution/Monitor.

            • benzphetamine

              diphenhydramine increases and benzphetamine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • benztropine

              benztropine and diphenhydramine both decrease cholinergic effects/transmission. Use Caution/Monitor. Additive anticholinergic adverse effects may be seen with concurrent use.

            • bethanechol

              bethanechol increases and diphenhydramine decreases cholinergic effects/transmission. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • brexanolone

              brexanolone, diphenhydramine. Either increases toxicity of the other by sedation. Use Caution/Monitor.

            • brexpiprazole

              diphenhydramine will increase the level or effect of brexpiprazole by affecting hepatic enzyme CYP2D6 metabolism. Modify Therapy/Monitor Closely. Administer a quarter of brexpiprazole dose if coadministered with a moderate CYP2D6 inhibitor PLUS a strong/moderate CYP3A4 inhibitor.

            • bromocriptine

              bromocriptine, phenylephrine. Either increases effects of the other by pharmacodynamic synergism. Use Caution/Monitor. Hypertension, V tach.

            • brompheniramine

              brompheniramine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              brompheniramine and diphenhydramine both increase sedation. Use Caution/Monitor.

            • bupivacaine implant

              acetaminophen, bupivacaine implant. Either increases toxicity of the other by Other (see comment). Use Caution/Monitor. Comment: Local anesthetics may increase the risk of developing methemoglobinemia when concurrently exposed to drugs that also cause methemoglobinemia.

            • buprenorphine

              diphenhydramine and buprenorphine both increase sedation. Use Caution/Monitor.

            • buprenorphine buccal

              buprenorphine buccal increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • buprenorphine buccal

              diphenhydramine and buprenorphine buccal both increase sedation. Use Caution/Monitor.

            • busulfan

              acetaminophen increases levels of busulfan by decreasing metabolism. Use Caution/Monitor. Use of acetaminophen prior to (< 72 hours) or concurrently with busulfan may result in decreased clearance of busulfan due to acetaminophen-induced decreases in glutathione levels.

            • butabarbital

              butabarbital increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine and butabarbital both increase sedation. Use Caution/Monitor.

            • butalbital

              diphenhydramine and butalbital both increase sedation. Use Caution/Monitor.

              butalbital increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • butorphanol

              butorphanol increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine and butorphanol both increase sedation. Use Caution/Monitor.

            • caffeine

              diphenhydramine increases and caffeine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              caffeine and phenylephrine both decrease sedation. Use Caution/Monitor.

            • carbachol

              carbachol increases and diphenhydramine decreases cholinergic effects/transmission. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • carbinoxamine

              carbinoxamine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • carbinoxamine

              carbinoxamine and diphenhydramine both increase sedation. Use Caution/Monitor.

            • carisoprodol

              diphenhydramine and carisoprodol both increase sedation. Use Caution/Monitor.

            • carvedilol

              diphenhydramine will increase the level or effect of carvedilol by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

            • cenobamate

              cenobamate, diphenhydramine. Either increases effects of the other by sedation. Use Caution/Monitor.

            • cevimeline

              cevimeline increases and diphenhydramine decreases cholinergic effects/transmission. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • chloral hydrate

              diphenhydramine and chloral hydrate both increase sedation. Use Caution/Monitor.

              chloral hydrate increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • chlordiazepoxide

              diphenhydramine and chlordiazepoxide both increase sedation. Use Caution/Monitor.

              chlordiazepoxide increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • chlorpheniramine

              chlorpheniramine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              chlorpheniramine and diphenhydramine both increase sedation. Use Caution/Monitor.

            • chlorpromazine

              diphenhydramine and chlorpromazine both increase sedation. Use Caution/Monitor.

              diphenhydramine decreases levels of chlorpromazine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.

              diphenhydramine decreases levels of chlorpromazine by pharmacodynamic antagonism. Use Caution/Monitor.

              chlorpromazine increases effects of diphenhydramine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia.

              chlorpromazine, phenylephrine. Mechanism: unknown. Use Caution/Monitor. Risk of cardiac arrhythmia or sudden death, more likely w/thioridazine than other phenothiazines. Interaction more likely in certain predisposed pts. only.

              chlorpromazine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • chlorzoxazone

              diphenhydramine and chlorzoxazone both increase sedation. Use Caution/Monitor.

            • cinnarizine

              cinnarizine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • cinnarizine

              cinnarizine and diphenhydramine both increase sedation. Use Caution/Monitor.

            • cisatracurium

              cisatracurium and diphenhydramine both decrease cholinergic effects/transmission. Use Caution/Monitor.

            • clemastine

              clemastine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              clemastine and diphenhydramine both increase sedation. Use Caution/Monitor.

            • clobazam

              diphenhydramine, clobazam. Other (see comment). Use Caution/Monitor. Comment: Concomitant administration can increase the potential for CNS effects (e.g., increased sedation or respiratory depression).

            • clomipramine

              clomipramine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • clomipramine

              diphenhydramine will increase the level or effect of clomipramine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

              diphenhydramine and clomipramine both decrease cholinergic effects/transmission. Use Caution/Monitor.

              diphenhydramine and clomipramine both increase sedation. Use Caution/Monitor.

            • clonazepam

              clonazepam increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine and clonazepam both increase sedation. Use Caution/Monitor.

            • clorazepate

              diphenhydramine and clorazepate both increase sedation. Use Caution/Monitor.

              clorazepate increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • clozapine

              clozapine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine decreases levels of clozapine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.

              diphenhydramine and clozapine both increase sedation. Use Caution/Monitor.

              diphenhydramine decreases levels of clozapine by pharmacodynamic antagonism. Use Caution/Monitor.

              clozapine increases effects of diphenhydramine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia.

            • codeine

              diphenhydramine decreases effects of codeine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Prevents conversion of codeine to its active metabolite morphine.

              diphenhydramine and codeine both increase sedation. Use Caution/Monitor.

              codeine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • cyclizine

              cyclizine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              cyclizine and diphenhydramine both increase sedation. Use Caution/Monitor.

              cyclizine and diphenhydramine both decrease cholinergic effects/transmission. Use Caution/Monitor.

            • cyclobenzaprine

              cyclobenzaprine and diphenhydramine both decrease cholinergic effects/transmission. Use Caution/Monitor.

              diphenhydramine and cyclobenzaprine both increase sedation. Use Caution/Monitor.

            • cyproheptadine

              cyproheptadine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • cyproheptadine

              cyproheptadine and diphenhydramine both increase sedation. Use Caution/Monitor.

            • dantrolene

              diphenhydramine and dantrolene both increase sedation. Use Caution/Monitor.

            • dapsone topical

              acetaminophen increases toxicity of dapsone topical by altering metabolism. Modify Therapy/Monitor Closely. May induce methemoglobinemia .

            • daridorexant

              diphenhydramine and daridorexant both increase sedation. Modify Therapy/Monitor Closely. Coadministration increases risk of CNS depression, which can lead to additive impairment of psychomotor performance and cause daytime impairment.

            • darifenacin

              darifenacin and diphenhydramine both decrease cholinergic effects/transmission. Use Caution/Monitor.

            • desflurane

              desflurane and diphenhydramine both increase sedation. Use Caution/Monitor.

            • desipramine

              diphenhydramine will increase the level or effect of desipramine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

              diphenhydramine and desipramine both increase sedation. Use Caution/Monitor.

              desipramine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • deutetrabenazine

              diphenhydramine and deutetrabenazine both increase sedation. Use Caution/Monitor.

            • dexchlorpheniramine

              dexchlorpheniramine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • dexchlorpheniramine

              dexchlorpheniramine and diphenhydramine both increase sedation. Use Caution/Monitor.

            • dexfenfluramine

              diphenhydramine increases and dexfenfluramine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              dexfenfluramine and phenylephrine both increase sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Use Caution/Monitor.

              dexfenfluramine and phenylephrine both decrease sedation. Use Caution/Monitor.

            • dexmedetomidine

              dexmedetomidine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine and dexmedetomidine both increase sedation. Use Caution/Monitor.

            • dexmethylphenidate

              dexmethylphenidate and phenylephrine both decrease sedation. Use Caution/Monitor.

              diphenhydramine increases and dexmethylphenidate decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              dexmethylphenidate and phenylephrine both increase sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Use Caution/Monitor.

            • dextroamphetamine

              dextroamphetamine and phenylephrine both decrease sedation. Use Caution/Monitor.

              diphenhydramine increases and dextroamphetamine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              dextroamphetamine and phenylephrine both increase sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Use Caution/Monitor.

            • dextromoramide

              diphenhydramine and dextromoramide both increase sedation. Use Caution/Monitor.

              dextromoramide increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • diamorphine

              diphenhydramine and diamorphine both increase sedation. Use Caution/Monitor.

              diamorphine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • diazepam

              diphenhydramine and diazepam both increase sedation. Use Caution/Monitor.

            • diethylpropion

              diethylpropion and phenylephrine both decrease sedation. Use Caution/Monitor.

              diethylpropion and phenylephrine both increase sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Use Caution/Monitor.

            • diazepam intranasal

              diazepam intranasal, diphenhydramine. Either increases effects of the other by pharmacodynamic synergism. Use Caution/Monitor. Coadministration may potentiate the CNS-depressant effects of each drug.

            • dicyclomine

              dicyclomine and diphenhydramine both decrease cholinergic effects/transmission. Use Caution/Monitor.

            • diethylpropion

              diphenhydramine increases and diethylpropion decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • difelikefalin

              difelikefalin and diphenhydramine both increase sedation. Use Caution/Monitor.

            • difenoxin hcl

              difenoxin hcl increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine and difenoxin hcl both increase sedation. Use Caution/Monitor.

            • dimenhydrinate

              dimenhydrinate increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              dimenhydrinate and diphenhydramine both increase sedation. Use Caution/Monitor.

            • diphenhydramine

              diphenhydramine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • diphenoxylate hcl

              diphenhydramine and diphenoxylate hcl both increase sedation. Use Caution/Monitor.

            • diphenoxylate hcl

              diphenoxylate hcl increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • dipipanone

              diphenhydramine and dipipanone both increase sedation. Use Caution/Monitor.

              dipipanone increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • dobutamine

              dobutamine and phenylephrine both decrease sedation. Use Caution/Monitor.

              diphenhydramine increases and dobutamine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              dobutamine and phenylephrine both increase sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Use Caution/Monitor.

            • donepezil

              donepezil increases and diphenhydramine decreases cholinergic effects/transmission. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • dopamine

              dopamine and phenylephrine both decrease sedation. Use Caution/Monitor.

              dopamine and phenylephrine both increase sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Use Caution/Monitor.

            • donepezil transdermal

              donepezil transdermal, diphenhydramine. Either decreases effects of the other by pharmacodynamic antagonism. Use Caution/Monitor.

            • dopamine

              diphenhydramine increases and dopamine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • dopexamine

              dopexamine and phenylephrine both increase sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Use Caution/Monitor.

              diphenhydramine increases and dopexamine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              dopexamine and phenylephrine both decrease sedation. Use Caution/Monitor.

            • dosulepin

              diphenhydramine and dosulepin both decrease cholinergic effects/transmission. Use Caution/Monitor.

              diphenhydramine and dosulepin both increase sedation. Use Caution/Monitor.

            • doxepin

              doxepin increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • doxepin

              diphenhydramine and doxepin both decrease cholinergic effects/transmission. Use Caution/Monitor.

              diphenhydramine and doxepin both increase sedation. Use Caution/Monitor.

            • doxylamine

              diphenhydramine and doxylamine both increase sedation. Use Caution/Monitor.

            • droperidol

              diphenhydramine decreases levels of droperidol by pharmacodynamic antagonism. Use Caution/Monitor.

              droperidol increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine and droperidol both increase sedation. Use Caution/Monitor.

              diphenhydramine decreases levels of droperidol by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.

              droperidol increases effects of diphenhydramine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia.

            • droxidopa

              phenylephrine and droxidopa both increase sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Use Caution/Monitor. May increase risk for supine hypertension

            • duloxetine

              diphenhydramine will increase the level or effect of duloxetine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

            • echothiophate iodide

              echothiophate iodide increases and diphenhydramine decreases cholinergic effects/transmission. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • eltrombopag

              eltrombopag increases levels of acetaminophen by decreasing metabolism. Use Caution/Monitor. UGT inhibition; significance of interaction unclear.

            • ephedrine

              ephedrine, phenylephrine. Either increases effects of the other by pharmacodynamic synergism. Use Caution/Monitor.

              ephedrine and phenylephrine both decrease sedation. Use Caution/Monitor.

              diphenhydramine increases and ephedrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              ephedrine and phenylephrine both increase sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Use Caution/Monitor.

            • epinephrine

              epinephrine and phenylephrine both decrease sedation. Use Caution/Monitor.

              epinephrine and phenylephrine both increase sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Use Caution/Monitor.

              diphenhydramine increases and epinephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • epinephrine inhaled

              phenylephrine, epinephrine inhaled. Either increases effects of the other by sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Use Caution/Monitor.

            • epinephrine racemic

              diphenhydramine increases and epinephrine racemic decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • epinephrine racemic

              epinephrine racemic and phenylephrine both decrease sedation. Use Caution/Monitor.

              epinephrine racemic and phenylephrine both increase sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Use Caution/Monitor.

            • esketamine intranasal

              esketamine intranasal, diphenhydramine. Either increases toxicity of the other by sedation. Modify Therapy/Monitor Closely.

            • estazolam

              estazolam increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine and estazolam both increase sedation. Use Caution/Monitor.

            • ethanol

              ethanol increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine and ethanol both increase sedation. Use Caution/Monitor.

            • etomidate

              etomidate and diphenhydramine both increase sedation. Use Caution/Monitor.

            • exenatide injectable solution

              exenatide injectable solution will decrease the level or effect of acetaminophen by unspecified interaction mechanism. Use Caution/Monitor. To avoid potential interaction, give acetaminophen at least 1 hour before or 4 hours after exenatide injection.

            • exenatide injectable suspension

              exenatide injectable suspension will decrease the level or effect of acetaminophen by unspecified interaction mechanism. Use Caution/Monitor. To avoid potential interaction, give acetaminophen at least 1 hour before or 4 hours after exenatide injection.

            • fenfluramine

              fenfluramine and phenylephrine both decrease sedation. Use Caution/Monitor.

              fenfluramine and phenylephrine both increase sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Use Caution/Monitor.

            • fenfluramine

              diphenhydramine increases and fenfluramine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • fentanyl

              fentanyl, diphenhydramine. Either increases toxicity of the other by pharmacodynamic synergism. Modify Therapy/Monitor Closely. Coadministration of fentanyl with anticholinergics may increase risk for urinary retention and/or severe constipation, which may lead to paralytic ileus.

            • fentanyl intranasal

              fentanyl intranasal, diphenhydramine. Either increases toxicity of the other by pharmacodynamic synergism. Modify Therapy/Monitor Closely. Coadministration of fentanyl with anticholinergics may increase risk for urinary retention and/or severe constipation, which may lead to paralytic ileus.

            • fentanyl transdermal

              fentanyl transdermal, diphenhydramine. Either increases toxicity of the other by pharmacodynamic synergism. Modify Therapy/Monitor Closely. Coadministration of fentanyl with anticholinergics may increase risk for urinary retention and/or severe constipation, which may lead to paralytic ileus.

            • fentanyl transmucosal

              fentanyl transmucosal, diphenhydramine. Either increases toxicity of the other by pharmacodynamic synergism. Modify Therapy/Monitor Closely. Coadministration of fentanyl with anticholinergics may increase risk for urinary retention and/or severe constipation, which may lead to paralytic ileus.

            • fesoterodine

              diphenhydramine and fesoterodine both decrease cholinergic effects/transmission. Use Caution/Monitor.

            • finerenone

              acetaminophen will increase the level or effect of finerenone by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Monitor serum potassium during initiation and dosage adjustment of either finererone or moderate CYP3A4 inhibitors. Adjust finererone dosage as needed.

            • flavoxate

              diphenhydramine and flavoxate both decrease cholinergic effects/transmission. Use Caution/Monitor.

            • flecainide

              diphenhydramine will increase the level or effect of flecainide by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

            • flibanserin

              diphenhydramine and flibanserin both increase sedation. Modify Therapy/Monitor Closely. Risk for sedation increased if flibanserin is coadministration with other CNS depressants.

              acetaminophen will increase the level or effect of flibanserin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Increased flibanserin adverse effects may occur if coadministered with multiple weak CYP3A4 inhibitors.

            • fluphenazine

              fluphenazine increases effects of diphenhydramine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia.

              diphenhydramine decreases levels of fluphenazine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.

              fluphenazine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine and fluphenazine both increase sedation. Use Caution/Monitor.

              fluphenazine, phenylephrine. Mechanism: unknown. Use Caution/Monitor. Risk of cardiac arrhythmia or sudden death, more likely w/thioridazine than other phenothiazines. Interaction more likely in certain predisposed pts. only.

              diphenhydramine decreases levels of fluphenazine by pharmacodynamic antagonism. Use Caution/Monitor.

            • imatinib

              imatinib decreases levels of acetaminophen by decreasing hepatic clearance. Modify Therapy/Monitor Closely. In vitro, imatinib was found to inhibit acetaminophen O-glucuronidation (Ki value of 58.5 micro-M) at therapeutic levels; avoid chronic acetaminophen therapy with imatinib; if occasional acetaminophen administered, do not exceed 1300 mg/day.

            • flurazepam

              diphenhydramine and flurazepam both increase sedation. Use Caution/Monitor.

              flurazepam increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • formoterol

              diphenhydramine increases and formoterol decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              formoterol and phenylephrine both increase sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Use Caution/Monitor.

              formoterol and phenylephrine both decrease sedation. Use Caution/Monitor.

            • gabapentin

              gabapentin, diphenhydramine. Either increases effects of the other by pharmacodynamic synergism. Modify Therapy/Monitor Closely. Coadministration of CNS depressants can result in serious, life-threatening, and fatal respiratory depression. Use lowest dose possible and monitor for respiratory depression and sedation.

            • haloperidol

              haloperidol increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • gabapentin enacarbil

              gabapentin enacarbil, diphenhydramine. Either increases effects of the other by pharmacodynamic synergism. Modify Therapy/Monitor Closely. Coadministration of CNS depressants can result in serious, life-threatening, and fatal respiratory depression. Use lowest dose possible and monitor for respiratory depression and sedation.

            • galantamine

              galantamine increases and diphenhydramine decreases cholinergic effects/transmission. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • ganaxolone

              diphenhydramine and ganaxolone both increase sedation. Use Caution/Monitor.

            • glycopyrrolate

              diphenhydramine and glycopyrrolate both decrease cholinergic effects/transmission. Use Caution/Monitor.

            • glycopyrrolate inhaled

              diphenhydramine and glycopyrrolate inhaled both decrease cholinergic effects/transmission. Use Caution/Monitor.

            • glycopyrronium tosylate topical

              glycopyrronium tosylate topical, diphenhydramine. Either increases effects of the other by pharmacodynamic synergism. Use Caution/Monitor. Coadministration of glycopyrronium tosylate topical with other anticholinergic medications may result in additive anticholinergic adverse effects.

            • gotu kola

              gotu kola increases effects of diphenhydramine by pharmacodynamic synergism. Use Caution/Monitor. May enhance CNS depression.

            • haloperidol

              diphenhydramine will increase the level or effect of haloperidol by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

              diphenhydramine and haloperidol both increase sedation. Use Caution/Monitor.

              diphenhydramine decreases levels of haloperidol by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.

              diphenhydramine decreases levels of haloperidol by pharmacodynamic antagonism. Use Caution/Monitor.

              haloperidol increases effects of diphenhydramine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia.

            • hawthorn

              hawthorn increases effects of diphenhydramine by pharmacodynamic synergism. Use Caution/Monitor. May enhance CNS depression.

            • henbane

              diphenhydramine and henbane both decrease cholinergic effects/transmission. Use Caution/Monitor.

            • homatropine

              diphenhydramine and homatropine both decrease cholinergic effects/transmission. Use Caution/Monitor.

            • hops

              hops increases effects of diphenhydramine by pharmacodynamic synergism. Use Caution/Monitor. May enhance CNS depression.

            • huperzine A

              huperzine A increases and diphenhydramine decreases cholinergic effects/transmission. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • hyaluronidase

              diphenhydramine decreases effects of hyaluronidase by Other (see comment). Use Caution/Monitor. Comment: Antihistamines, when given in large systemic doses, may render tissues partially resistant to the action of hyaluronidase. Patients may require larger amounts of hyaluronidase for equivalent dispersing effect.

            • hydralazine

              hydralazine, phenylephrine. Mechanism: pharmacodynamic antagonism. Use Caution/Monitor. Sympathomimetics can antagonize the activity of some antihypertensive agents.

            • hydrocodone

              diphenhydramine will increase the level or effect of hydrocodone by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Hydromorphone (<3% of the circulating parent hydrocodone) is mainly formed by CYP2D6 mediated O-demethylation of hydrocodone. Hydromorphone may contribute to the total analgesic effect of hydrocodone.

            • hydromorphone

              diphenhydramine will increase the level or effect of hydromorphone by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

              diphenhydramine and hydromorphone both increase sedation. Use Caution/Monitor.

              hydromorphone increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • hydroxyzine

              diphenhydramine and hydroxyzine both increase sedation. Use Caution/Monitor.

              hydroxyzine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • hyoscyamine

              diphenhydramine and hyoscyamine both decrease cholinergic effects/transmission. Use Caution/Monitor.

            • iloperidone

              iloperidone increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • hyoscyamine spray

              diphenhydramine and hyoscyamine spray both decrease cholinergic effects/transmission. Use Caution/Monitor.

            • iloperidone

              diphenhydramine will increase the level or effect of iloperidone by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

              diphenhydramine and iloperidone both increase sedation. Use Caution/Monitor.

              diphenhydramine decreases levels of iloperidone by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.

              diphenhydramine decreases levels of iloperidone by pharmacodynamic antagonism. Use Caution/Monitor.

              iloperidone increases effects of diphenhydramine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia.

            • imipramine

              imipramine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine and imipramine both decrease cholinergic effects/transmission. Use Caution/Monitor.

              diphenhydramine and imipramine both increase sedation. Use Caution/Monitor.

              diphenhydramine will increase the level or effect of imipramine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

            • indacaterol, inhaled

              phenylephrine increases effects of indacaterol, inhaled by Other (see comment). Use Caution/Monitor. Comment: If additional adrenergic drugs are to be administered by any route, they should be used with caution because the sympathetic effects of indacaterol may be potentiated.

            • ipratropium

              diphenhydramine and ipratropium both decrease cholinergic effects/transmission. Use Caution/Monitor. Due to the poor systemic absorption of ipratropium, interaction unlikely at regularly recommended dosages.

            • insulin degludec

              phenylephrine decreases effects of insulin degludec by pharmacodynamic antagonism. Modify Therapy/Monitor Closely. Sympathomimetics increase blood glucose by stimulating alpha and beta receptors; this action results in increased hepatic glucose production, glycogenolysis, and decreased insulin secretion.

            • insulin degludec/insulin aspart

              phenylephrine decreases effects of insulin degludec/insulin aspart by pharmacodynamic antagonism. Modify Therapy/Monitor Closely. Sympathomimetics increase blood glucose by stimulating alpha and beta receptors; this action results in increased hepatic glucose production, glycogenolysis, and decreased insulin secretion.

            • insulin inhaled

              phenylephrine decreases effects of insulin inhaled by pharmacodynamic antagonism. Modify Therapy/Monitor Closely. Sympathomimetics increase blood glucose by stimulating alpha and beta receptors; this action results in increased hepatic glucose production, glycogenolysis, and decreased insulin secretion.

            • isavuconazonium sulfate

              acetaminophen will increase the level or effect of isavuconazonium sulfate by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • isoniazid

              isoniazid will increase the level or effect of acetaminophen by affecting hepatic enzyme CYP2E1 metabolism. Use Caution/Monitor.

            • isoproterenol

              isoproterenol and phenylephrine both decrease sedation. Use Caution/Monitor.

              diphenhydramine increases and isoproterenol decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              isoproterenol and phenylephrine both increase sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Use Caution/Monitor.

            • ivacaftor

              acetaminophen increases levels of ivacaftor by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Monitor when coadministered with weak CYP3A4 inhibitors .

            • kava

              kava increases effects of diphenhydramine by pharmacodynamic synergism. Use Caution/Monitor. May enhance CNS depression.

            • ketotifen, ophthalmic

              ketotifen, ophthalmic increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • ketamine

              ketamine and diphenhydramine both increase sedation. Use Caution/Monitor.

            • ketotifen, ophthalmic

              diphenhydramine and ketotifen, ophthalmic both increase sedation. Use Caution/Monitor.

            • lasmiditan

              lasmiditan, diphenhydramine. Either increases effects of the other by sedation. Use Caution/Monitor. Coadministration of lasmiditan and other CNS depressant drugs, including alcohol have not been evaluated in clinical studies. Lasmiditan may cause sedation, as well as other cognitive and/or neuropsychiatric adverse reactions.

            • lemborexant

              acetaminophen will increase the level or effect of lemborexant by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Lower nightly dose of lemborexant recommended if coadministered with weak CYP3A4 inhibitors. See drug monograph for specific dosage modification.

              lemborexant, diphenhydramine. Either increases effects of the other by sedation. Modify Therapy/Monitor Closely. Dosage adjustment may be necessary if lemborexant is coadministered with other CNS depressants because of potentially additive effects.

            • levalbuterol

              levalbuterol and phenylephrine both increase sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Use Caution/Monitor.

              diphenhydramine increases and levalbuterol decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              levalbuterol and phenylephrine both decrease sedation. Use Caution/Monitor.

            • levonorgestrel oral/ethinylestradiol/ferrous bisglycinate

              levonorgestrel oral/ethinylestradiol/ferrous bisglycinate will decrease the level or effect of acetaminophen by unknown mechanism. Use Caution/Monitor.

              acetaminophen increases levels of levonorgestrel oral/ethinylestradiol/ferrous bisglycinate by decreasing hepatic clearance. Use Caution/Monitor. Coadministration of ascorbic acid and certain combined hormonal contraceptives (CHCs) containing EE may increase plasma EE concentrations, possibly by inhibition of conjugation.

            • levodopa

              diphenhydramine, levodopa. Other (see comment). Use Caution/Monitor. Comment: Anticholinergic agents may enhance the therapeutic effects of levodopa; however, anticholinergic agents can exacerbate tardive dyskinesia. In high dosage, anticholinergics may decrease the effects of levodopa by delaying its GI absorption. .

            • levorphanol

              levorphanol increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • levorphanol

              diphenhydramine and levorphanol both increase sedation. Use Caution/Monitor.

            • lisdexamfetamine

              lisdexamfetamine and phenylephrine both increase sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Use Caution/Monitor.

              lisdexamfetamine and phenylephrine both decrease sedation. Use Caution/Monitor.

              diphenhydramine increases and lisdexamfetamine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • lixisenatide

              lixisenatide will decrease the level or effect of acetaminophen by inhibition of GI absorption. Applies only to oral form of both agents. Modify Therapy/Monitor Closely. GLP1 agonists delay gastric emptying, which may affect absorption of concomitantly administered oral medications. No effects on acetaminophen Cmax and Tmax were observed when acetaminophen was administered 1 hr before lixisenatide. When administered 1 or 4 hr after lixisenatide, acetaminophen Cmax was decreased by 29% and 31% respectively and median Tmax was delayed by 2 and 1.75 hr, respectively.

            • lofepramine

              diphenhydramine will increase the level or effect of lofepramine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

              diphenhydramine and lofepramine both decrease cholinergic effects/transmission. Use Caution/Monitor.

              diphenhydramine and lofepramine both increase sedation. Use Caution/Monitor.

              lofepramine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • lofexidine

              lofexidine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine and lofexidine both increase sedation. Use Caution/Monitor.

            • lomitapide

              acetaminophen increases levels of lomitapide by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Lomitapide dose should not exceed 30 mg/day.

            • loprazolam

              loprazolam increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine and loprazolam both increase sedation. Use Caution/Monitor.

            • lorazepam

              lorazepam increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine and lorazepam both increase sedation. Use Caution/Monitor.

            • lormetazepam

              diphenhydramine and lormetazepam both increase sedation. Use Caution/Monitor.

              lormetazepam increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • loxapine

              diphenhydramine and loxapine both increase sedation. Use Caution/Monitor.

              diphenhydramine decreases levels of loxapine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.

              diphenhydramine decreases levels of loxapine by pharmacodynamic antagonism. Use Caution/Monitor.

              loxapine increases effects of diphenhydramine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia.

              loxapine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • loxapine inhaled

              diphenhydramine and loxapine inhaled both increase sedation. Use Caution/Monitor.

              loxapine inhaled increases effects of diphenhydramine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia.

              loxapine inhaled increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine decreases levels of loxapine inhaled by pharmacodynamic antagonism. Use Caution/Monitor.

            • lurasidone

              lurasidone, diphenhydramine. Either increases toxicity of the other by Other (see comment). Use Caution/Monitor. Comment: Potential for increased CNS depressant effects when used concurrently; monitor for increased adverse effects and toxicity.

            • maprotiline

              maprotiline increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • maprotiline

              diphenhydramine and maprotiline both decrease cholinergic effects/transmission. Use Caution/Monitor.

              diphenhydramine and maprotiline both increase sedation. Use Caution/Monitor.

            • marijuana

              diphenhydramine and marijuana both increase sedation. Use Caution/Monitor.

              marijuana increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • meclizine

              diphenhydramine and meclizine both decrease cholinergic effects/transmission. Use Caution/Monitor.

            • melatonin

              melatonin increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • melatonin

              diphenhydramine and melatonin both increase sedation. Use Caution/Monitor.

            • meperidine

              meperidine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine and meperidine both increase sedation. Use Caution/Monitor.

            • meprobamate

              meprobamate increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine and meprobamate both increase sedation. Use Caution/Monitor.

            • metaproterenol

              metaproterenol and phenylephrine both decrease sedation. Use Caution/Monitor.

              diphenhydramine increases and metaproterenol decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              metaproterenol and phenylephrine both increase sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Use Caution/Monitor.

            • metaxalone

              diphenhydramine and metaxalone both increase sedation. Use Caution/Monitor.

            • methadone

              methadone increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • methadone

              diphenhydramine and methadone both increase sedation. Use Caution/Monitor.

            • methamphetamine

              methamphetamine and phenylephrine both increase sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Use Caution/Monitor.

              diphenhydramine increases and methamphetamine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine will increase the level or effect of methamphetamine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

              methamphetamine and phenylephrine both decrease sedation. Use Caution/Monitor.

            • methocarbamol

              diphenhydramine and methocarbamol both increase sedation. Use Caution/Monitor.

            • methyldopa

              methyldopa increases effects of phenylephrine by unknown mechanism. Use Caution/Monitor.

            • methscopolamine

              diphenhydramine and methscopolamine both decrease cholinergic effects/transmission. Use Caution/Monitor.

            • methylenedioxymethamphetamine

              diphenhydramine increases and methylenedioxymethamphetamine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              methylenedioxymethamphetamine and phenylephrine both increase sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Use Caution/Monitor.

              methylenedioxymethamphetamine and phenylephrine both decrease sedation. Use Caution/Monitor.

            • metoprolol

              diphenhydramine will increase the level or effect of metoprolol by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

            • midazolam

              midazolam increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • mexiletine

              diphenhydramine will increase the level or effect of mexiletine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

            • midazolam

              diphenhydramine and midazolam both increase sedation. Use Caution/Monitor.

            • midazolam intranasal

              midazolam intranasal, diphenhydramine. Either increases toxicity of the other by pharmacodynamic synergism. Modify Therapy/Monitor Closely. Concomitant use of barbiturates, alcohol, or other CNS depressants may increase risk of hypoventilation, airway obstruction, desaturation, or apnea and may contribute to profound and/or prolonged drug effect.

              acetaminophen will increase the level or effect of midazolam intranasal by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Coadministration of mild CYP3A4 inhibitors with midazolam intranasal may cause higher midazolam systemic exposure, which may prolong sedation.

            • midodrine

              midodrine and phenylephrine both decrease sedation. Use Caution/Monitor.

              diphenhydramine increases and midodrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              midodrine and phenylephrine both increase sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Use Caution/Monitor.

            • mipomersen

              mipomersen, acetaminophen. Either increases toxicity of the other by Other (see comment). Use Caution/Monitor. Comment: Both drugs have potential to increase hepatic enzymes; monitor LFTs.

            • mirtazapine

              diphenhydramine and mirtazapine both increase sedation. Use Caution/Monitor.

              mirtazapine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • modafinil

              modafinil and phenylephrine both decrease sedation. Use Caution/Monitor.

              diphenhydramine increases and modafinil decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • morphine

              diphenhydramine and morphine both increase sedation. Use Caution/Monitor.

              diphenhydramine will increase the level or effect of morphine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

              morphine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • motherwort

              diphenhydramine and motherwort both increase sedation. Use Caution/Monitor.

              motherwort increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • moxonidine

              moxonidine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine and moxonidine both increase sedation. Use Caution/Monitor.

            • nabilone

              nabilone increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine and nabilone both increase sedation. Use Caution/Monitor.

            • nadolol

              nadolol increases effects of phenylephrine by pharmacodynamic synergism. Use Caution/Monitor. Risk of acute hypertensive episode (rare).

            • nalbuphine

              diphenhydramine and nalbuphine both increase sedation. Use Caution/Monitor.

            • nalbuphine

              nalbuphine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • nebivolol

              diphenhydramine will increase the level or effect of nebivolol by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

            • neostigmine

              neostigmine increases and diphenhydramine decreases cholinergic effects/transmission. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • norepinephrine

              norepinephrine and phenylephrine both decrease sedation. Use Caution/Monitor.

              norepinephrine and phenylephrine both increase sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Use Caution/Monitor.

              diphenhydramine increases and norepinephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • nortriptyline

              nortriptyline increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine and nortriptyline both decrease cholinergic effects/transmission. Use Caution/Monitor.

              diphenhydramine and nortriptyline both increase sedation. Use Caution/Monitor.

              diphenhydramine will increase the level or effect of nortriptyline by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

            • olanzapine

              diphenhydramine decreases levels of olanzapine by pharmacodynamic antagonism. Use Caution/Monitor.

              olanzapine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine and olanzapine both increase sedation. Use Caution/Monitor.

              diphenhydramine decreases levels of olanzapine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.

              olanzapine increases effects of diphenhydramine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia.

            • oliceridine

              diphenhydramine will increase the level or effect of oliceridine by affecting hepatic enzyme CYP2D6 metabolism. Modify Therapy/Monitor Closely. If concomitant use is necessary, may require less frequent oliceridine dosing. Closely monitor for respiratory depression and sedation and titrate subsequent doses accordingly. If inhibitor is discontinued, consider increase oliceridine dosage until stable drug effects are achieved. Monitor for signs of opioid withdrawal.

            • olodaterol inhaled

              phenylephrine and olodaterol inhaled both increase sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Use Caution/Monitor. Caution with coadministration of adrenergic drugs by any route because of additive sympathetic effects

            • onabotulinumtoxinA

              onabotulinumtoxinA and diphenhydramine both decrease cholinergic effects/transmission. Use Caution/Monitor.

            • opium tincture

              diphenhydramine and opium tincture both increase sedation. Use Caution/Monitor.

              opium tincture increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • orphenadrine

              diphenhydramine and orphenadrine both decrease cholinergic effects/transmission. Use Caution/Monitor.

              diphenhydramine and orphenadrine both increase sedation. Use Caution/Monitor.

            • oxazepam

              oxazepam increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • ospemifene

              diphenhydramine, ospemifene. Either increases levels of the other by plasma protein binding competition. Modify Therapy/Monitor Closely.

            • oxazepam

              diphenhydramine and oxazepam both increase sedation. Use Caution/Monitor.

            • oxybutynin

              diphenhydramine and oxybutynin both decrease cholinergic effects/transmission. Use Caution/Monitor.

            • oxybutynin topical

              diphenhydramine and oxybutynin topical both decrease cholinergic effects/transmission. Use Caution/Monitor.

            • oxybutynin transdermal

              diphenhydramine and oxybutynin transdermal both decrease cholinergic effects/transmission. Use Caution/Monitor.

            • oxycodone

              oxycodone increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine and oxycodone both increase sedation. Use Caution/Monitor.

              diphenhydramine will increase the level or effect of oxycodone by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

            • oxymetazoline topical

              oxymetazoline topical and phenylephrine both increase sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Use Caution/Monitor.

            • oxymorphone

              diphenhydramine will increase the level or effect of oxymorphone by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

              diphenhydramine and oxymorphone both increase sedation. Use Caution/Monitor.

            • oxymorphone

              oxymorphone increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • oxytocin

              oxytocin increases effects of phenylephrine by pharmacodynamic synergism. Use Caution/Monitor.

            • paliperidone

              diphenhydramine decreases levels of paliperidone by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.

              diphenhydramine decreases levels of paliperidone by pharmacodynamic antagonism. Use Caution/Monitor.

              paliperidone increases effects of diphenhydramine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia.

              diphenhydramine and paliperidone both increase sedation. Use Caution/Monitor.

              paliperidone increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • pancuronium

              diphenhydramine and pancuronium both decrease cholinergic effects/transmission. Use Caution/Monitor.

            • papaveretum

              papaveretum increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • papaveretum

              diphenhydramine and papaveretum both increase sedation. Use Caution/Monitor.

            • papaverine

              diphenhydramine and papaverine both increase sedation. Use Caution/Monitor.

            • passion flower

              passion flower increases effects of diphenhydramine by pharmacodynamic synergism. Use Caution/Monitor. May enhance CNS depression.

            • pentazocine

              diphenhydramine and pentazocine both increase sedation. Use Caution/Monitor.

              pentazocine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • pentobarbital

              pentobarbital increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine and pentobarbital both increase sedation. Use Caution/Monitor.

            • perampanel

              perampanel and diphenhydramine both increase sedation. Use Caution/Monitor.

            • perphenazine

              perphenazine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              perphenazine, phenylephrine. Mechanism: unknown. Use Caution/Monitor. Risk of cardiac arrhythmia or sudden death, more likely w/thioridazine than other phenothiazines. Interaction more likely in certain predisposed pts. only.

            • perphenazine

              diphenhydramine and perphenazine both increase sedation. Use Caution/Monitor.

              diphenhydramine decreases levels of perphenazine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.

              diphenhydramine decreases levels of perphenazine by pharmacodynamic antagonism. Use Caution/Monitor.

              perphenazine increases effects of diphenhydramine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia.

            • phendimetrazine

              phendimetrazine and phenylephrine both decrease sedation. Use Caution/Monitor.

              diphenhydramine increases and phendimetrazine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              phendimetrazine and phenylephrine both increase sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Use Caution/Monitor.

            • phenelzine

              phenelzine increases effects of diphenhydramine by Other (see comment). Modify Therapy/Monitor Closely. Comment: Coadministration of phenelzine and antihistamines may result in additive CNS depressant effects. MAO inhibitors also prolong and intensify anticholinergic effects of antihistamines. .

            • phenobarbital

              phenobarbital increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • phenobarbital

              diphenhydramine and phenobarbital both increase sedation. Use Caution/Monitor.

            • phentermine

              phentermine and phenylephrine both decrease sedation. Use Caution/Monitor.

              diphenhydramine increases and phentermine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              phentermine and phenylephrine both increase sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Use Caution/Monitor.

            • phenylephrine

              diphenhydramine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • pholcodine

              pholcodine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • phenylephrine PO

              diphenhydramine increases and phenylephrine PO decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor. .

            • pholcodine

              diphenhydramine and pholcodine both increase sedation. Use Caution/Monitor.

            • physostigmine

              physostigmine increases and diphenhydramine decreases cholinergic effects/transmission. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • pilocarpine

              pilocarpine increases and diphenhydramine decreases cholinergic effects/transmission. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • pimozide

              pimozide increases effects of diphenhydramine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia.

              diphenhydramine decreases levels of pimozide by pharmacodynamic antagonism. Use Caution/Monitor.

              pimozide increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine and pimozide both increase sedation. Use Caution/Monitor.

              diphenhydramine decreases levels of pimozide by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.

            • pindolol

              pindolol increases effects of phenylephrine by pharmacodynamic synergism. Use Caution/Monitor. Risk of acute hypertensive episode (rare).

            • pirbuterol

              diphenhydramine increases and pirbuterol decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • pirbuterol

              pirbuterol and phenylephrine both decrease sedation. Use Caution/Monitor.

              pirbuterol and phenylephrine both increase sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Use Caution/Monitor.

            • pralidoxime

              diphenhydramine and pralidoxime both decrease cholinergic effects/transmission. Use Caution/Monitor.

            • pregabalin

              pregabalin, diphenhydramine. Either increases effects of the other by pharmacodynamic synergism. Modify Therapy/Monitor Closely. Coadministration of CNS depressants can result in serious, life-threatening, and fatal respiratory depression. Use lowest dose possible and monitor for respiratory depression and sedation.

            • primidone

              primidone increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine and primidone both increase sedation. Use Caution/Monitor.

            • prochlorperazine

              diphenhydramine and prochlorperazine both increase sedation. Use Caution/Monitor.

              diphenhydramine decreases levels of prochlorperazine by pharmacodynamic antagonism. Use Caution/Monitor.

              prochlorperazine increases effects of diphenhydramine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia.

              diphenhydramine decreases levels of prochlorperazine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.

              prochlorperazine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              prochlorperazine, phenylephrine. Mechanism: unknown. Use Caution/Monitor. Risk of cardiac arrhythmia or sudden death, more likely w/thioridazine than other phenothiazines. Interaction more likely in certain predisposed pts. only.

            • promazine

              promazine, phenylephrine. Mechanism: unknown. Use Caution/Monitor. Risk of cardiac arrhythmia or sudden death, more likely w/thioridazine than other phenothiazines. Interaction more likely in certain predisposed pts. only.

            • promethazine

              diphenhydramine and promethazine both increase sedation. Use Caution/Monitor.

              diphenhydramine decreases levels of promethazine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.

              diphenhydramine decreases levels of promethazine by pharmacodynamic antagonism. Use Caution/Monitor.

              promethazine increases effects of diphenhydramine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia.

            • promethazine

              promethazine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              promethazine, phenylephrine. Mechanism: unknown. Use Caution/Monitor. Risk of cardiac arrhythmia or sudden death, more likely w/thioridazine than other phenothiazines. Interaction more likely in certain predisposed pts. only.

            • propafenone

              diphenhydramine will increase the level or effect of propafenone by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

            • propantheline

              diphenhydramine and propantheline both decrease cholinergic effects/transmission. Use Caution/Monitor.

            • propofol

              propofol increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              propofol and diphenhydramine both increase sedation. Use Caution/Monitor.

            • propranolol

              diphenhydramine will increase the level or effect of propranolol by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

              propranolol increases effects of phenylephrine by pharmacodynamic synergism. Use Caution/Monitor. Risk of acute hypertensive episode (rare).

            • propylhexedrine

              phenylephrine and propylhexedrine both decrease sedation. Use Caution/Monitor.

              phenylephrine and propylhexedrine both increase sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Use Caution/Monitor.

              diphenhydramine increases and propylhexedrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • protriptyline

              diphenhydramine and protriptyline both decrease cholinergic effects/transmission. Use Caution/Monitor.

              diphenhydramine and protriptyline both increase sedation. Use Caution/Monitor.

              protriptyline increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • pseudoephedrine

              phenylephrine and pseudoephedrine both increase sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Use Caution/Monitor.

            • pyridostigmine

              pyridostigmine increases and diphenhydramine decreases cholinergic effects/transmission. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • quazepam

              diphenhydramine and quazepam both increase sedation. Use Caution/Monitor.

              quazepam increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • quetiapine

              diphenhydramine decreases levels of quetiapine by pharmacodynamic antagonism. Use Caution/Monitor.

              quetiapine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine decreases levels of quetiapine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.

              diphenhydramine and quetiapine both increase sedation. Use Caution/Monitor.

              quetiapine increases effects of diphenhydramine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia.

            • ramelteon

              diphenhydramine and ramelteon both increase sedation. Use Caution/Monitor.

            • rasagiline

              rasagiline increases effects of phenylephrine by pharmacodynamic synergism. Use Caution/Monitor. Risk of acute hypertensive episode.

            • rapacuronium

              diphenhydramine and rapacuronium both decrease cholinergic effects/transmission. Use Caution/Monitor.

            • risperidone

              diphenhydramine decreases levels of risperidone by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.

              diphenhydramine decreases levels of risperidone by pharmacodynamic antagonism. Use Caution/Monitor.

              risperidone increases effects of diphenhydramine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia.

              risperidone increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine and risperidone both increase sedation. Use Caution/Monitor.

            • rocuronium

              diphenhydramine and rocuronium both decrease cholinergic effects/transmission. Use Caution/Monitor.

            • safinamide

              phenylephrine and safinamide both increase sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Use Caution/Monitor. Monitor patients for hypertension if safinamide is prescribed concomitantly with prescription or nonprescription sympathomimetics, including nasal, oral, or ophthalmic decongestants and cold remedies.

            • salmeterol

              diphenhydramine increases and salmeterol decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              salmeterol and phenylephrine both increase sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Use Caution/Monitor.

              salmeterol and phenylephrine both decrease sedation. Use Caution/Monitor.

            • scopolamine

              diphenhydramine and scopolamine both decrease cholinergic effects/transmission. Use Caution/Monitor.

            • scullcap

              scullcap increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • scullcap

              diphenhydramine and scullcap both increase sedation. Use Caution/Monitor.

            • secobarbital

              secobarbital increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine and secobarbital both increase sedation. Use Caution/Monitor.

            • selegiline

              selegiline increases effects of phenylephrine by pharmacodynamic synergism. Use Caution/Monitor. Risk of acute hypertensive episode.

            • sevoflurane

              sevoflurane and diphenhydramine both increase sedation. Use Caution/Monitor.

            • serdexmethylphenidate/dexmethylphenidate

              serdexmethylphenidate/dexmethylphenidate and phenylephrine both decrease sedation. Use Caution/Monitor.

              serdexmethylphenidate/dexmethylphenidate and phenylephrine both increase sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Use Caution/Monitor.

            • shepherd's purse

              diphenhydramine and shepherd's purse both increase sedation. Use Caution/Monitor.

              shepherd's purse increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • solifenacin

              diphenhydramine and solifenacin both decrease cholinergic effects/transmission. Use Caution/Monitor.

            • solriamfetol

              phenylephrine and solriamfetol both increase sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Use Caution/Monitor.

            • stiripentol

              stiripentol, diphenhydramine. Either increases effects of the other by sedation. Use Caution/Monitor. Concomitant use stiripentol with other CNS depressants, including alcohol, may increase the risk of sedation and somnolence.

            • succinylcholine

              succinylcholine increases and diphenhydramine decreases cholinergic effects/transmission. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • sufentanil

              sufentanil increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine and sufentanil both increase sedation. Use Caution/Monitor.

            • tamoxifen

              diphenhydramine decreases effects of tamoxifen by decreasing metabolism. Use Caution/Monitor. Inhibition of CYP2D6 metabolism to tamoxifen's active metabolite, endoxifen.

            • tapentadol

              tapentadol increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • tamsulosin

              diphenhydramine increases levels of tamsulosin by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

            • tapentadol

              diphenhydramine and tapentadol both increase sedation. Use Caution/Monitor.

            • tazemetostat

              acetaminophen will increase the level or effect of tazemetostat by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • temazepam

              temazepam increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine and temazepam both increase sedation. Use Caution/Monitor.

            • terbutaline

              terbutaline and phenylephrine both decrease sedation. Use Caution/Monitor.

              terbutaline and phenylephrine both increase sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Use Caution/Monitor.

              diphenhydramine increases and terbutaline decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • tetracaine

              tetracaine, acetaminophen. Other (see comment). Use Caution/Monitor. Comment: Monitor for signs of methemoglobinemia when methemoglobin-inducing drugs are coadministered.

            • thioridazine

              diphenhydramine decreases levels of thioridazine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.

              diphenhydramine decreases levels of thioridazine by pharmacodynamic antagonism. Use Caution/Monitor.

              thioridazine increases effects of diphenhydramine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia.

              thioridazine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              thioridazine, phenylephrine. Mechanism: unknown. Use Caution/Monitor. Risk of cardiac arrhythmia or sudden death, more likely w/thioridazine than other phenothiazines. Interaction more likely in certain predisposed pts. only.

              diphenhydramine and thioridazine both increase sedation. Use Caution/Monitor.

            • thiothixene

              diphenhydramine and thiothixene both increase sedation. Use Caution/Monitor.

              diphenhydramine decreases levels of thiothixene by pharmacodynamic antagonism. Use Caution/Monitor.

              thiothixene increases effects of diphenhydramine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia.

              diphenhydramine decreases levels of thiothixene by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.

              thiothixene increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • timolol

              diphenhydramine will increase the level or effect of timolol by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

              timolol increases effects of phenylephrine by pharmacodynamic synergism. Use Caution/Monitor. Risk of acute hypertensive episode (rare).

            • tinidazole

              acetaminophen will increase the level or effect of tinidazole by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • tiotropium

              diphenhydramine and tiotropium both decrease cholinergic effects/transmission. Use Caution/Monitor.

            • topiramate

              topiramate increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Modify Therapy/Monitor Closely.

            • tolterodine

              diphenhydramine and tolterodine both decrease cholinergic effects/transmission. Use Caution/Monitor.

            • topiramate

              diphenhydramine and topiramate both increase sedation. Modify Therapy/Monitor Closely.

            • tramadol

              diphenhydramine decreases effects of tramadol by decreasing metabolism. Use Caution/Monitor. Decreased conversion of tramadol to active metabolite.

              diphenhydramine decreases effects of tramadol by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Decreased conversion of tramadol to active metabolite.

              diphenhydramine and tramadol both increase sedation. Use Caution/Monitor.

              tramadol increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • trazodone

              diphenhydramine and trazodone both increase sedation. Use Caution/Monitor.

              trazodone increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • triazolam

              triazolam increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine and triazolam both increase sedation. Use Caution/Monitor.

            • triclofos

              diphenhydramine and triclofos both increase sedation. Use Caution/Monitor.

              triclofos increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • trifluoperazine

              diphenhydramine and trifluoperazine both increase sedation. Use Caution/Monitor.

              diphenhydramine decreases levels of trifluoperazine by inhibition of GI absorption. Applies only to oral form of both agents. Use Caution/Monitor.

              diphenhydramine decreases levels of trifluoperazine by pharmacodynamic antagonism. Use Caution/Monitor.

              trifluoperazine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              trifluoperazine, phenylephrine. Mechanism: unknown. Use Caution/Monitor. Risk of cardiac arrhythmia or sudden death, more likely w/thioridazine than other phenothiazines. Interaction more likely in certain predisposed pts. only.

              trifluoperazine increases effects of diphenhydramine by pharmacodynamic synergism. Use Caution/Monitor. Additive anticholinergic effects, possible hypoglycemia.

            • trihexyphenidyl

              diphenhydramine and trihexyphenidyl both decrease cholinergic effects/transmission. Use Caution/Monitor. Potential for additive anticholinergic effects.

            • trimipramine

              trimipramine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

            • trimipramine

              diphenhydramine and trimipramine both decrease cholinergic effects/transmission. Use Caution/Monitor.

              diphenhydramine and trimipramine both increase sedation. Use Caution/Monitor.

            • triprolidine

              triprolidine increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Use Caution/Monitor.

              diphenhydramine and triprolidine both increase sedation. Use Caution/Monitor.

            • trospium chloride

              diphenhydramine and trospium chloride both decrease cholinergic effects/transmission. Use Caution/Monitor.

            • warfarin

              acetaminophen increases effects of warfarin by anticoagulation. Use Caution/Monitor.

            • xylometazoline

              phenylephrine and xylometazoline both decrease sedation. Use Caution/Monitor.

              phenylephrine and xylometazoline both increase sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Use Caution/Monitor.

            Minor (88)

            • acetazolamide

              acetazolamide decreases levels of acetaminophen by increasing metabolism. Minor/Significance Unknown. Enhanced metabolism incr levels of hepatotoxic metabolites.

            • albiglutide

              albiglutide decreases levels of acetaminophen by unspecified interaction mechanism. Minor/Significance Unknown.

            • alfuzosin

              alfuzosin, phenylephrine. Either decreases effects of the other by Mechanism: pharmacodynamic antagonism. Minor/Significance Unknown.

            • antithrombin alfa

              acetaminophen increases effects of antithrombin alfa by unknown mechanism. Minor/Significance Unknown.

            • antithrombin III

              acetaminophen increases effects of antithrombin III by unknown mechanism. Minor/Significance Unknown.

            • argatroban

              acetaminophen increases effects of argatroban by unknown mechanism. Minor/Significance Unknown.

            • aripiprazole

              diphenhydramine will increase the level or effect of aripiprazole by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • asenapine

              asenapine, phenylephrine. Either decreases effects of the other by Mechanism: pharmacodynamic antagonism. Minor/Significance Unknown.

            • ashwagandha

              ashwagandha increases effects of diphenhydramine by pharmacodynamic synergism. Minor/Significance Unknown. May enhance CNS depression.

            • bemiparin

              acetaminophen increases effects of bemiparin by unknown mechanism. Minor/Significance Unknown.

            • bivalirudin

              acetaminophen increases effects of bivalirudin by unknown mechanism. Minor/Significance Unknown.

            • brimonidine

              brimonidine increases effects of diphenhydramine by pharmacodynamic synergism. Minor/Significance Unknown. Increased CNS depression.

            • carbamazepine

              carbamazepine decreases levels of acetaminophen by increasing metabolism. Minor/Significance Unknown. Enhanced metabolism incr levels of hepatotoxic metabolites.

            • chlorpromazine

              diphenhydramine will increase the level or effect of chlorpromazine by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • cholestyramine

              cholestyramine decreases levels of acetaminophen by inhibition of GI absorption. Applies only to oral form of both agents. Minor/Significance Unknown.

            • clonazepam

              clonazepam decreases levels of acetaminophen by increasing metabolism. Minor/Significance Unknown. Enhanced metabolism incr levels of hepatotoxic metabolites.

            • colestipol

              colestipol decreases levels of acetaminophen by inhibition of GI absorption. Applies only to oral form of both agents. Minor/Significance Unknown.

            • dalteparin

              acetaminophen increases effects of dalteparin by unknown mechanism. Minor/Significance Unknown.

            • desipramine

              diphenhydramine and desipramine both decrease cholinergic effects/transmission. Minor/Significance Unknown.

              desipramine and diphenhydramine both decrease cholinergic effects/transmission. Minor/Significance Unknown.

            • desmopressin

              desmopressin increases effects of phenylephrine by pharmacodynamic synergism. Minor/Significance Unknown.

            • dexfenfluramine

              diphenhydramine will increase the level or effect of dexfenfluramine by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • dextroamphetamine

              diphenhydramine will increase the level or effect of dextroamphetamine by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • dextromethorphan

              diphenhydramine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • diazepam

              diazepam decreases levels of acetaminophen by increasing metabolism. Minor/Significance Unknown. Enhanced metabolism incr levels of hepatotoxic metabolites.

            • dimenhydrinate

              dimenhydrinate increases toxicity of diphenhydramine by pharmacodynamic synergism. Minor/Significance Unknown. Additive anticholinergic effects.

            • disulfiram

              disulfiram will increase the level or effect of acetaminophen by affecting hepatic enzyme CYP2E1 metabolism. Minor/Significance Unknown.

            • donepezil

              diphenhydramine will increase the level or effect of donepezil by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

              donepezil decreases effects of diphenhydramine by pharmacodynamic antagonism. Minor/Significance Unknown.

            • doxazosin

              doxazosin, phenylephrine. Either decreases effects of the other by Mechanism: pharmacodynamic antagonism. Minor/Significance Unknown.

            • doxepin

              diphenhydramine will increase the level or effect of doxepin by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • encainide

              diphenhydramine will increase the level or effect of encainide by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • enoxaparin

              acetaminophen increases effects of enoxaparin by unknown mechanism. Minor/Significance Unknown.

            • ethanol

              ethanol will decrease the level or effect of acetaminophen by affecting hepatic enzyme CYP2E1 metabolism. Minor/Significance Unknown.

              ethanol increases toxicity of acetaminophen by decreasing metabolism. Minor/Significance Unknown.

            • ethosuximide

              ethosuximide decreases levels of acetaminophen by increasing metabolism. Minor/Significance Unknown. Enhanced metabolism incr levels of hepatotoxic metabolites.

            • eucalyptus

              eucalyptus increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Minor/Significance Unknown.

              diphenhydramine and eucalyptus both increase sedation. Minor/Significance Unknown.

            • felbamate

              felbamate decreases levels of acetaminophen by increasing metabolism. Minor/Significance Unknown. Enhanced metabolism incr levels of hepatotoxic metabolites.

            • fesoterodine

              diphenhydramine will increase the level or effect of fesoterodine by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • fondaparinux

              acetaminophen increases effects of fondaparinux by unknown mechanism. Minor/Significance Unknown.

            • fosphenytoin

              fosphenytoin decreases levels of acetaminophen by increasing metabolism. Minor/Significance Unknown. Enhanced metabolism incr levels of hepatotoxic metabolites.

            • green tea

              green tea increases effects of acetaminophen by pharmacodynamic synergism. Minor/Significance Unknown. (Theoretical, due to caffeine content).

            • heparin

              acetaminophen increases effects of heparin by unknown mechanism. Minor/Significance Unknown.

            • isoniazid

              isoniazid increases toxicity of acetaminophen by unknown mechanism. Minor/Significance Unknown.

            • lacosamide

              lacosamide decreases levels of acetaminophen by increasing metabolism. Minor/Significance Unknown. Enhanced metabolism incr levels of hepatotoxic metabolites.

            • lamotrigine

              lamotrigine decreases levels of acetaminophen by increasing metabolism. Minor/Significance Unknown. Enhanced metabolism incr levels of hepatotoxic metabolites.

            • levetiracetam

              levetiracetam decreases levels of acetaminophen by increasing metabolism. Minor/Significance Unknown. Enhanced metabolism incr levels of hepatotoxic metabolites.

            • liraglutide

              liraglutide decreases levels of acetaminophen by unspecified interaction mechanism. Minor/Significance Unknown.

            • lorazepam

              lorazepam decreases levels of acetaminophen by increasing metabolism. Minor/Significance Unknown. Enhanced metabolism incr levels of hepatotoxic metabolites.

            • methsuximide

              methsuximide decreases levels of acetaminophen by increasing metabolism. Minor/Significance Unknown. Enhanced metabolism incr levels of hepatotoxic metabolites.

            • metoclopramide

              metoclopramide increases levels of acetaminophen by enhancing GI absorption. Applies only to oral form of both agents. Minor/Significance Unknown.

            • metronidazole

              metronidazole will increase the level or effect of acetaminophen by affecting hepatic enzyme CYP2E1 metabolism. Minor/Significance Unknown.

            • moxisylyte

              moxisylyte, phenylephrine. Either decreases effects of the other by Mechanism: pharmacodynamic antagonism. Minor/Significance Unknown.

            • fluoxetine

              diphenhydramine will increase the level or effect of fluoxetine by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • fluphenazine

              diphenhydramine will increase the level or effect of fluphenazine by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • galantamine

              diphenhydramine will increase the level or effect of galantamine by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

              galantamine decreases effects of diphenhydramine by pharmacodynamic antagonism. Minor/Significance Unknown.

            • loratadine

              diphenhydramine will increase the level or effect of loratadine by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • nettle

              nettle increases effects of diphenhydramine by pharmacodynamic synergism. Minor/Significance Unknown. (High dose nettle; theoretical interaction) May enhance CNS depression.

            • nitazoxanide

              nitazoxanide, diphenhydramine. Either increases levels of the other by Mechanism: plasma protein binding competition. Minor/Significance Unknown.

            • oxcarbazepine

              oxcarbazepine decreases levels of acetaminophen by increasing metabolism. Minor/Significance Unknown. Enhanced metabolism incr levels of hepatotoxic metabolites.

            • oxybutynin

              oxybutynin decreases levels of acetaminophen by unspecified interaction mechanism. Minor/Significance Unknown.

            • oxybutynin topical

              oxybutynin topical decreases levels of acetaminophen by unspecified interaction mechanism. Minor/Significance Unknown.

            • oxybutynin transdermal

              oxybutynin transdermal decreases levels of acetaminophen by unspecified interaction mechanism. Minor/Significance Unknown.

            • oxycodone

              diphenhydramine decreases effects of oxycodone by decreasing metabolism. Minor/Significance Unknown. Decreased conversion of oxycodone to active metabolite morphine.

            • paroxetine

              diphenhydramine will increase the level or effect of paroxetine by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • perhexiline

              diphenhydramine will increase the level or effect of perhexiline by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • perphenazine

              diphenhydramine will increase the level or effect of perphenazine by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • phenindione

              acetaminophen increases effects of phenindione by unknown mechanism. Minor/Significance Unknown.

            • phenobarbital

              phenobarbital decreases levels of acetaminophen by increasing metabolism. Minor/Significance Unknown. Enhanced metabolism incr levels of hepatotoxic metabolites.

            • phenoxybenzamine

              phenoxybenzamine, phenylephrine. Either decreases effects of the other by Mechanism: pharmacodynamic antagonism. Minor/Significance Unknown.

            • phentolamine

              phentolamine, phenylephrine. Either decreases effects of the other by Mechanism: pharmacodynamic antagonism. Minor/Significance Unknown.

            • phenytoin

              phenytoin decreases levels of acetaminophen by increasing metabolism. Minor/Significance Unknown. Enhanced metabolism incr levels of hepatotoxic metabolites.

            • prazosin

              prazosin, phenylephrine. Either decreases effects of the other by Mechanism: pharmacodynamic antagonism. Minor/Significance Unknown.

            • primidone

              primidone decreases levels of acetaminophen by increasing metabolism. Minor/Significance Unknown. Enhanced metabolism incr levels of hepatotoxic metabolites.

            • prochlorperazine

              diphenhydramine will increase the level or effect of prochlorperazine by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • promazine

              diphenhydramine will increase the level or effect of promazine by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • promethazine

              diphenhydramine will increase the level or effect of promethazine by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • protamine

              acetaminophen increases effects of protamine by unknown mechanism. Minor/Significance Unknown.

            • rifabutin

              rifabutin decreases levels of acetaminophen by increasing metabolism. Minor/Significance Unknown. Enhanced metabolism incr levels of hepatotoxic metabolites.

            • rifampin

              rifampin decreases levels of acetaminophen by increasing metabolism. Minor/Significance Unknown. Enhanced metabolism incr levels of hepatotoxic metabolites.

            • risperidone

              diphenhydramine will increase the level or effect of risperidone by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • rufinamide

              rufinamide decreases levels of acetaminophen by increasing metabolism. Minor/Significance Unknown. Enhanced metabolism incr levels of hepatotoxic metabolites.

            • ruxolitinib

              acetaminophen will increase the level or effect of ruxolitinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Minor/Significance Unknown.

            • ruxolitinib topical

              acetaminophen will increase the level or effect of ruxolitinib topical by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Minor/Significance Unknown.

            • sage

              sage increases and phenylephrine decreases sedation. Effect of interaction is not clear, use caution. Minor/Significance Unknown.

              diphenhydramine and sage both increase sedation. Minor/Significance Unknown.

            • Siberian ginseng

              Siberian ginseng increases effects of diphenhydramine by pharmacodynamic synergism. Minor/Significance Unknown. May enhance CNS depression.

            • silodosin

              silodosin, phenylephrine. Either decreases effects of the other by Mechanism: pharmacodynamic antagonism. Minor/Significance Unknown.

            • terazosin

              terazosin, phenylephrine. Either decreases effects of the other by Mechanism: pharmacodynamic antagonism. Minor/Significance Unknown.

            • tiagabine

              tiagabine decreases levels of acetaminophen by increasing metabolism. Minor/Significance Unknown. Enhanced metabolism incr levels of hepatotoxic metabolites.

            • tolterodine

              diphenhydramine will increase the level or effect of tolterodine by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • topiramate

              topiramate decreases levels of acetaminophen by increasing metabolism. Minor/Significance Unknown. Enhanced metabolism incr levels of hepatotoxic metabolites.

            Previous
            Next:

            Adverse Effects

            Frequency Not Defined

            Hypertension

            Hypotension

            Reflex tachycardia

            Severe peripheral and visceral vasoconstriction

            Tachycardia

            Dizziness

            Excitability

            Headache

            Restlessness

            Sedation

            Sleepiness

            Tremor

            Dermatologic rash

            Increased appetite

            Xerostomia

            Anemia blood dyscrasias (neutropenia, pancytopenia, leukopenia)

            Bilirubin and alkaline phosphatase may increase

            Urinary retention

            Previous
            Next:

            Warnings

            Contraindications

            Hypersensitivity

            Use within 14 days of MAO inhibitor therapy

            To sedate child

            Children <12 years

            Concomitant administration with other products containing acetaminophen or diphenhydramine

            Cautions

            Ask healthcare professional if history of asthma or COPD, cough with mucus, or couch caused by smoking, emphysema, or chronic bronchitis, high blood pressure, heart disease, enlarged prostate, urination problems, thyroid disorder, diabetes, glaucoma, or diagnosed with condition requiring warfarin therapy

            Medication is to be used exactly as directed; an overdose of acetaminophen can damage the liver or cause death; taking too much diphenhydramine can lead to serious heart problems, seizures, coma, or death

            Not for use to make a child sleepy; some brands are not approved for use in anyone younger than 12 years old

            Dangerous drug interaction can occur with MAO inhibitors, including isocarboxazid, linezolid, phenelzine, rasagiline, selegiline, and tranylcypromine

            Cardiovascular disease (bradycardia, partial heart block or severe arteriosclerosis when administering phenylephrine)

            Acetaminophen hepatotoxicity possible in chronic alcoholics following various dose levels; before taking this medication, ask healthcare professional if experienced previous liver disease, or if taking more than 3 alcoholic beverages per day

            Acetaminophen: Risk for rare, but serious skin reactions that can be fatal; these reactions include Stevens-Johnson Syndrome (SJS), toxic epidermal necrolysis (TEN), and acute generalized exanthematous pustulosis (AGEP); symptoms may include skin redness, blisters and rash

            Severe or recurrent pain or high or continued fever may indicate a serious illness

            Acetaminophen contained in many OTC products and combined use with these products may result in toxicity due to cumulative doses exceeding recommended maximum dose

            Diphenhydramine may cause significant confusional symptoms

            Diphenhydramine not for administration to premature or full-term neonates

            Previous
            Next:

            Pregnancy & Lactation

            Pregnancy

            Ask a healthcare professional

            Lactation

            Ask a healthcare professional

            Pregnancy Categories

            A: Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.

            B: May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.

            C: Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.

            D: Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.

            X: Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.

            NA: Information not available.

            Previous
            Next:

            Pharmacology

            Mechanism of Action

            Acetaminophen: Blocks pain impulse generation peripherally & may inhibit the prostaglandin generation in CNS; reduces fever by inhibiting hypothalamic heat-regulating center

            Phenylephrine: Vasoconstrictor & decongestant that relieves symptoms resulting from irritation of upper respiratory tract tissue; shrinks swollen mucous membranes, reduces nasal congestion & tissue hyperemia

            Diphenhydramine: Competitively blocks histamine from binding to H1 receptors; significant antimuscarinic activity & penetrates CNS, which causes pronounced tendency to induce sedation

            Previous
            Next:

            Images

            No images available for this drug.
            Previous
            Next:

            Patient Handout

            A Patient Handout is not currently available for this monograph.
            Previous
            Medscape prescription drug monographs are based on FDA-approved labeling information, unless otherwise noted, combined with additional data derived from primary medical literature.