Diphenhydramine

ATC code

R06AA02

Therapeutic class

First-generation antihistamine, H1 antagonist · Aminoalkyl ether

Forms

oral tablet, oral capsule, oral solution, injectable solution

Brand names

Benadryl (US) · Nytol (UK) · Nautamine (FR) · Soñodor (ES)

Overall confidence

medium

Regulatory sources consulted

AEMPS CIMA Ficha Técnica 72308 (for Dimenhydrinate)
CredibleMeds.org
Flockhart Table (CYP450)
AGS Beers Criteria
General Clinical Pharmacology Databases
AEMPS CIMA · nº registro 72308 ↗

Approved indications

Symptomatic treatment of allergic conditions such as rhinitis, conjunctivitis, and urticaria.
Short-term relief of insomnia.
Prevention and treatment of motion sickness.
Management of drug-induced extrapyramidal reactions (e.g., acute dystonia). · off-label

Contraindications

Absolute

Hypersensitivity to the drug, newborn or premature infants, lactating mothers, acute asthmatic attack.

Relative

Narrow-angle glaucoma, symptomatic prostatic hypertrophy, stenosing peptic ulcer, pyloroduodenal obstruction.

Clinical warnings

Major warning · May cause marked drowsiness. Avoid driving or operating machinery. Avoid concurrent use of alcohol or other CNS depressants. — Clinical Practice
Major warning · Use with caution in elderly patients due to high risk of anticholinergic effects (confusion, falls). Included in the Beers Criteria. — AGS Beers Criteria

Drug interactions

HighAlcoholV03AB16
Mechanism: Additive pharmacodynamic effect resulting in severe central nervous system (CNS) depression.
Recommendation: Avoid concomitant use.
Clinical Practice
HighMonoamine oxidase inhibitors (MAOIs)N06AF
Mechanism: MAOIs prolong and intensify the anticholinergic effects of diphenhydramine, increasing the risk of toxicity (hypertension, hyperpyrexia, delirium).
Recommendation: Concomitant use is contraindicated or should be avoided. Allow at least 14 days between discontinuation of the MAOI and initiation of diphenhydramine.
Clinical Practice

Adverse events

Common (≥1%)

drowsiness · dizziness · dry mouth · blurred vision · urinary retention · constipation · thickening of bronchial secretions

Rare but serious

anaphylaxis · agranulocytosis · hemolytic anemia · seizures · anticholinergic delirium · cardiac arrhythmias

Pregnancy and lactation

FDA category: B

Pregnancy: Use only if clearly needed. Lactation: Contraindicated. Excreted in breast milk and may cause sedation and other adverse effects in the infant.