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 oneIt reverses 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.
FDA-approved for
- allergy (~1946)
- insomnia (~1980)
Off-label
- insomnia
- dystonia
FDA label
Read the full label on DailyMed ↗
| 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
NO BOXED WARNINGS
Principal riskAnticholinergic burden; on every elderly deprescribing list
Classes and tags
Clinical profile
Legacy pregnancy categoryB
Defining liabilityLocal irritation, sensitization or administration-site injury; negligible systemic toxicity at usual use.
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