What it is used for
- Allergy symptoms (sneezing, runny nose, itchy or watery eyes)
- Hives and itchy skin
- Allergic reactions to insect bites or stings
- Sometimes used short-term for its sedating effect under guidance
- Relief of some cold-related symptoms in combination products
How it works
Diphenhydramine blocks histamine to relieve allergy symptoms. Because it acts on the brain, it commonly causes marked drowsiness.
How it is taken
Comes as tablets, capsules, liquids, and topical creams, and as an injection given by professionals in some settings. Oral forms are taken by mouth. Use it exactly as directed by your doctor, pharmacist, or the label, and do not exceed the recommended amount.
No doses here on purpose. The right strength and schedule depend on you — only a doctor or pharmacist should set them. Always follow your prescription and the label.
Common side effects
- Marked drowsiness
- Dry mouth, nose, and throat
- Dizziness
- Blurred vision
- Constipation
- Difficulty passing urine
Serious effects — get help
- Signs of a severe allergic reaction (swelling, breathing difficulty)
- Fast or irregular heartbeat
- Confusion or hallucinations (especially in older adults or with overdose)
- Seizures (rare)
If a reaction is severe — for example trouble breathing, swelling of the face or throat, or collapse — go to the nearest emergency room now or call your local emergency number. Do not wait for an online consultation.
Interactions to watch
- Alcohol (greatly increases drowsiness)
- Sedatives, sleeping tablets, strong painkillers
- Other antihistamines or anticholinergic medicines
- Some antidepressants (MAOIs)
Who should take care
- Tell your clinician if you are pregnant, planning pregnancy, or breastfeeding
- Strongly sedating — do not drive or operate machinery until you know how it affects you
- Use cautiously in older adults
- Caution with glaucoma, enlarged prostate, urinary or breathing problems
- Avoid if allergic to diphenhydramine