About diphenhydramine
First-generation antihistamine
Used for
- Severe allergic reactions as an adjunct to emergency treatment
- Allergic symptoms when oral treatment is unsuitable
Usual adult dose
Usually 10–50 mg by slow injection; up to 100 mg per dose in some situations.
Usual dose in children
Usually 1–2 mg/kg by slow injection, maximum 50 mg per dose; use depends on age and indication.
Common side effects
- Drowsiness and dizziness
- Dry mouth, blurred vision, or constipation
- Low blood pressure
- Confusion, especially in older adults
Important warnings
- Can cause marked sleepiness; avoid driving if affected.
- May worsen glaucoma, urinary retention, or breathing problems.
- Injection can cause low blood pressure or tissue injury if given incorrectly.
- Not a substitute for adrenaline in anaphylaxis.
Pregnancy
Use only when clinically needed; pregnancy safety information is limited.
Breastfeeding
May cause infant sleepiness and reduce milk supply, especially with repeated doses.
Interactions
- Alcohol, opioids, and sedatives increase drowsiness.
- Other anticholinergic medicines increase dry mouth, constipation, and urinary problems.
- Monoamine oxidase inhibitors may intensify or prolong effects.
AI-generated from general medical knowledge, not from this product's official leaflet. It may be incomplete or out of date. Not medical advice — ask a pharmacist or doctor before making any decision.