Diphenhydramine
BENADRYL
Pronunciation: dye-fen-HYE-dra-meen
“Dippin’ hydra’s mean Bean drill”
“wears two hats” – max antihistamine and antimuscarinic
What it isFirst-generation H1 antagonist; allergy, insomnia, motion sickness and acute dystonia.
Why this oneReverses acute dystonic reactions within minutes and is available without prescription.
What limits itHeavy anticholinergic burden and sedation — it is on every deprescribing list for the elderly. Tolerance to the hypnotic effect is rapid.
Diphenhydramine prescription history
Animated chart of estimated U.S. prescriptions per year, Antiemetics (1946–2026). Diphenhydramine enters in 1946 (estimated).
FDA-approved for
- allergy (~1946)
- insomnia (~1980)
Off-label
- dystonia
Principal riskAnticholinergic burden; on every elderly deprescribing list
Classes and tags
Clinical profile
Legacy pregnancy categoryB
Defining liabilitySedation and impaired alertness, anticholinergic effects, and additive effects with alcohol or other CNS depressants; overdose can be serious.
FDA label
Read the full label on DailyMed ↗
NO BOXED WARNINGS
| FDA dosing | Population | Start | Target | Max |
|---|---|---|---|---|
| Hay fever / upper respiratory allergy or common cold symptoms (runny nose, sneezing, itchy watery eyes, itchy nose/throat) | Adults & children ≥12 yr | 1–2 tablets (25 mg each) q4–6h PRN | 1–2 tablets q4–6h PRN | 6 doses/24 h |
| Hay fever / upper respiratory allergy or common cold symptoms (runny nose, sneezing, itchy watery eyes, itchy nose/throat) | Children 6 to <12 yr | 1 tablet q4–6h PRN | 1 tablet q4–6h PRN | 6 doses/24 h |
Renal Undefined
Hepatic Undefined
Children under 6 yr: do not use.
Available strengths
- cap 25, 50 mg
- tab 25, 50 mg
Contraindications
- To make a child sleepy
- With any other diphenhydramine-containing product, even one used on skin
Cautions
- Ask a doctor before use: breathing problem (emphysema, chronic bronchitis), glaucoma, or trouble urinating due to enlarged prostate
- Ask a doctor or pharmacist before use if taking sedatives or tranquilizers
- When using: avoid alcohol; alcohol, sedatives, tranquilizers increase drowsiness; caution driving/operating machinery
Adverse reactions
- Marked drowsiness
- Excitability, especially in children
Pregnancy If pregnant, ask a health professional before use.
Lactation If breast-feeding, ask a health professional before use.
Cost
| Strength | #/mo | generic $/mo | CostPlus | |
|---|---|---|---|---|
| 25 mg | tab | 30 qd | $1.11 | not offered |
| 50 mg | tab | 30 qd | not offered | |
| 25 mg | cap | 30 qd | $1.60 | not offered |
| 50 mg | cap | 30 qd | $3.13 | not offered |
Other forms: Diphenhydramine injection (BENADRYL IM / IV)
Generic entry1982
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Memory aids: interaction avatars
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Self-check
- How rapidly can diphenhydramine reverse acute dystonia?
Within minutes. - How quickly does hypnotic tolerance develop?
Rapidly.