Benadryl (diphenhydramine)

What diphenhydramine is and how it works

Diphenhydramine is a first-generation antihistamine available without a prescription in most countries. Depending on the market and product, it is used to relieve allergy and cold symptoms (as Benadryl, in the US, Canada, and Australia) or as a short-term aid for occasional sleeplessness (in the UK and New Zealand). (1) (4)

Diphenhydramine causes noticeable drowsiness in most people and has real, current safety concerns: it is not recommended for regular use in older adults because of anticholinergic side effects (confusion, falls), and there is an ongoing, publicly documented pattern of dangerous misuse at high doses, particularly among teenagers following social-media trends. Use only as directed on the label or by a pharmacist or doctor, and never take more than the labelled dose.

Mechanism of action: how diphenhydramine works

Diphenhydramine is a first-generation H1-receptor antagonist with significant anticholinergic and sedative (CNS-penetrant) properties, which underlie both its antihistamine effect and its use as a short-term sleep aid, as well as its anticholinergic side-effect profile in older adults. (1) (4) (2)

What diphenhydramine is used for

Before taking diphenhydramine

Do not take / not appropriate for

• Do not use to make a child sleepy. (United States) (1)
• Do not use with any other product containing diphenhydramine, even one applied to the skin. (all countries) (1) (8)
• Do not use if you have a known hypersensitivity to diphenhydramine or a stenosing peptic ulcer or pyloroduodenal obstruction. (United Kingdom) (4)
• Children under 6 years should not use this product (US allergy/cold product); the UK sleep-aid tablet should not be used in anyone under 16 years. (United States, United Kingdom) (1) (4)

Tell your clinician about

• If you have a breathing problem such as emphysema or chronic bronchitis, glaucoma, or trouble urinating due to an enlarged prostate gland.
• If you have myasthenia gravis, epilepsy, narrow-angle glaucoma, asthma, or liver or kidney impairment.
• If you are 65 or older -- diphenhydramine is generally not recommended for regular use in older adults because of a real risk of confusion, falls, and other side effects (see Serious warnings).
• If you are taking sedatives, tranquilizers, or any other medicine that also causes drowsiness.
• If you are pregnant or breastfeeding.

How to take diphenhydramine

• Take only as directed on the product label, or as directed by a doctor or pharmacist -- do not exceed the stated dose or frequency.
• Marked drowsiness may occur; avoid alcoholic drinks while taking this medicine.
• Be careful when driving a motor vehicle or operating machinery until you know how this medicine affects you.
• Do not combine with any other product that also contains diphenhydramine, including topical creams or gels.

Procedures and treatment changes

Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (1) (2) (3) (4) (5) (6) (7) (8)

Missed dose

This medicine is generally taken only as needed for symptoms or occasional sleeplessness, not on a fixed daily schedule, so a 'missed dose' does not usually apply. Only take a dose when you need it and never take more than the labelled maximum in 24 hours.

Overdose

Contact a Poison Control Center immediately if you or someone else has taken more than the labelled dose, even without symptoms. Taking much higher than recommended doses -- including the pattern of intentional high-dose misuse sometimes called the 'Benadryl Challenge' that has circulated on social media -- can cause serious heart problems, seizures, coma, or death, and has been linked to confirmed deaths, particularly among teenagers. Seek emergency medical help for severe drowsiness, agitation, hallucinations, a fast or irregular heartbeat, seizures, or difficulty staying awake. (1) (2)

Side effects

Side effects and their urgency vary; report severe, persistent, or concerning symptoms.

Serious warnings

Interactions

• Alcohol, sedatives, and tranquilizers may increase drowsiness and should generally be avoided while taking diphenhydramine. (1)
• Diphenhydramine potentiates other CNS depressants, MAOIs, and other anticholinergic medicines. (4)
• Diphenhydramine inhibits the CYP2D6 liver enzyme, which can raise levels of medicines such as metoprolol and venlafaxine that are broken down by this pathway. (4)
• Do not combine with any other product also containing diphenhydramine, including topical (skin) products. (1) (8)

Pregnancy, breastfeeding, kidney/liver function, age

Monitoring

Before starting

• Review for enlarged prostate, glaucoma, breathing conditions, or urinary retention (ask a doctor first if any apply)
• Review for other sedating medicines or alcohol use
• Consider age -- avoid regular use in adults 65 and older where possible

During treatment

• Watch for excessive drowsiness, confusion, or unsteadiness, especially in older adults.
• Do not exceed the labelled dose or duration of use (typically not beyond 2 weeks for sleep-aid use without medical advice).
• Seek medical advice promptly if symptoms do not improve or if new symptoms develop.

Storage

Store at room temperature in the original packaging, out of reach of children.

Frequently asked questions

References

1. BENADRYL - diphenhydramine hydrochloride tablet, film coated -- Drug Facts labelU.S. Food and Drug Administration / DailyMed (NIH), OTC Drug Facts label, Kenvue (Benadryl Allergy Ultratab / diphenhydramine HCl 25 mg tablets) · United States · accessed 2026-07-31 · source 1
2. FDA warns about serious problems with high doses of the common over-the-counter allergy medicine diphenhydramine (Benadryl), following the social-media 'Benadryl Challenge'U.S. Food and Drug Administration public safety communication, reported by CBS News/NBC News/The Conversation (2020 original warning; 2025-2026 follow-up public-health reporting) · United States · accessed 2026-07-31 · source 2
3. 2023 American Geriatrics Society Beers CriteriaAmerican Geriatrics Society (AGS) Beers Criteria for Potentially Inappropriate Medication Use in Older Adults · United States (widely referenced international geriatric-prescribing standard) · accessed 2026-07-31 · source 3
4. Diphenhydramine Hydrochloride 25 mg Tablets -- Summary of Product Characteristics (SmPC)electronic medicines compendium (emc), United Kingdom -- Diphenhydramine Hydrochloride 25 mg Tablets Summary of Product Characteristics · United Kingdom · accessed 2026-07-31 · source 4
5. Diphenhydramine / diphenhydramine-paracetamol -- list of nationally authorised medicinal products (PSUSA/00001110/202411)European Medicines Agency (EMA) -- PSUSA (periodic safety update single assessment) list of nationally authorised medicinal products containing diphenhydramine · European Union · accessed 2026-07-31 · source 5
6. BENADRYL ALLERGY -- Health Canada Drug Product Database entry (DIN 02017849)Health Canada Drug Product Database (DPD) · Canada · accessed 2026-07-31 · source 6
7. BENADRYL ORIGINAL oral liquid -- ARTG entry 199371; related diphenhydramine-containing OTC productsTherapeutic Goods Administration (TGA), Australia · Australia · accessed 2026-07-31 · source 7
8. UNISOM SleepGels (diphenhydramine hydrochloride 50 mg) -- New Zealand Data SheetMedsafe (New Zealand regulator) -- Unisom SleepGels (diphenhydramine hydrochloride 50 mg) New Zealand Data Sheet · New Zealand · accessed 2026-07-31 · source 8

Brand names by country

Single-ingredient diphenhydramine names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.

Priority countries