Diphenhydramine
Diphenhydramine is a first-generation antihistamine commonly used to treat allergic reactions, hay fever, cold symptoms, and itching. It is also frequently used as a sleep aid due to its sedating properties.
Diphenhydramine is an antihistamine used for allergies, itching, and as a short-term sleep aid.
Key facts at a glance
- ATC
- D04AA32
- RxNorm
- 3498
- Generic
- Diphenhydramine
- Class
- atc-d04
- Brands
- Percogesic Reformulated Jan 2011, Wal-Dryl, Compoz, Wal-Dryl Childrens, Wal-Dryl-D, Wal-Dryl Allergy, Wal-Som Maximum Strength, Nytol, Banophen Cream, Sleep-Eze, Unisom Sleep, Scot-Tussin Allergy, Panadol PM, Rest Simply, Kids-Eeze Allergy
- Availability
- otc
- Pregnancy
- B
- Lactation
- caution
- Half-life (h)
- 8
- Onset (min)
- 30
- Duration (h)
- 6
- Routes
- oral, topical
- Forms
- tablet, capsule, oral solution, syrup, elixir, cream, gel, lotion, spray
- Regions
- United States, Canada, United Kingdom, European Union, Australia, Japan, India, worldwide
- Monitoring
- sedation, anticholinergic effects
This page is for informational purposes only.
Do not use this information to diagnose yourself or to replace a physician's advice. Always consult a qualified healthcare provider before starting, stopping, or changing any medication. If you believe you are experiencing a medical emergency, call your local emergency number immediately.
Dosage and administration
- Usual dose
- 500mg twice daily
- Maximum
- consult physician
- Frequency
- every 12 hours
- Instructions
- Follow physician instructions
- Duration limits
- as prescribed
- Monitoring
- standard
- Usual dose
- 250mg twice daily
- Maximum
- consult physician
- Frequency
- every 12 hours
- Instructions
- Follow physician instructions
- Duration limits
- as prescribed
- Monitoring
- standard
- Usual dose
- 400mg daily
- Maximum
- consult physician
- Frequency
- once daily
- Instructions
- Follow physician instructions
- Duration limits
- as prescribed
- Monitoring
- standard
Overdose information
Special Populations
9 groupspregnancy
first trimesteruse lowest effective dose
use only if clearly needed, avoid prolonged use
standard prenatal care
Use with caution and monitor for adverse effects.
pregnancy
second trimesteruse lowest effective dose
use only if clearly needed
standard prenatal care
Use with caution and monitor for adverse effects.
pregnancy
third trimesteravoid high doses close to delivery
avoid use near term as may increase risk of premature labor
monitor for uterine contractions
Use with caution and monitor for adverse effects.
lactation
breastfeedinguse lowest effective dose
take after breastfeeding and monitor infant for excessive drowsiness
observe infant for sedation, irritability or feeding changes
Use with caution and monitor for adverse effects.
pediatric_age
under 2 yearsdo not use
do not use in infants under 2 years of age due to risk of severe sedation and respiratory depression
emergency medical attention if used
Use of this medication in this population requires careful consideration of risks and benefits.
pediatric_age
2 to 12 yearsweight-based dosing, do not exceed recommended limits
consult healthcare provider before use, avoid in children with asthma
monitor for paradoxical excitement and respiratory depression
Use with caution and monitor for adverse effects.
geriatric
elderlyreduce dose, start with lowest effective dose
increased sensitivity to anticholinergic effects, use with caution in patients with glaucoma or urinary retention
monitor for confusion, falls and anticholinergic effects
Use with caution and monitor for adverse effects.
renal_impairment
severe renal impairmentreduce dose by 50% in severe renal impairment
adjust dosing interval, use with caution in patients on dialysis
monitor renal function and adjust dose accordingly
Use with caution and monitor for adverse effects.
hepatic_impairment
moderate to severe hepaticreduce dose by 50%
use with caution in patients with hepatic impairment
monitor for increased sedation and anticholinergic effects
Use with caution and monitor for adverse effects.
Statistics and clinical data
FDA approval year
FDA approval year for Diphenhydramine
Drug class
Antihistamine classification
Primary indications
Common therapeutic uses
Mechanism of action
Primary pharmacologic mechanism
Treatment of allergic reactions, seasonal allergies, hay fever, cold symptoms, itching/pruritus, and temporary sleep difficulties. May also be used for motion sickness and as an antiemetic.
Blocks H1 histamine receptors to reduce allergic symptoms and has anticholinergic effects. It crosses the blood-brain barrier, producing sedation.
Causes drowsiness; avoid driving or operating machinery. Do not use with alcohol or other CNS depressants. Use with caution in elderly, those with glaucoma, urinary retention, or heart conditions. Should only be used short-term for insomnia. Consult a healthcare provider before use.
Contraindications
Conditions and patient states where this medication should be avoided or used with caution.
Do not use (1)
Known allergy to this medication or its components
Use caution (1)
Consult healthcare provider for benefits vs risks assessment
Official drug label
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This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 26, 2026. · Read our editorial policy