diphenhydramine hydrochloride at a glance
Medicine class
Sedating H1 antihistamine with antimuscarinic activity.
Oral role
Relief of temporary sleep disturbance.
Cream role
Local relief of allergic itching, rashes, hives, stings and insect bites.
Driving
Do not drive, cycle or operate machinery if sleepy, dizzy, unsteady, visually impaired or unable to concentrate.
Alcohol
Avoid alcohol with oral diphenhydramine because it can substantially increase sedation and other adverse effects.
What is diphenhydramine hydrochloride used for?
Licensed uses differ by formulation.
Oral tablets: relief of temporary sleep disturbance.
Cream: relief of hives, itching, allergic rashes, stings and insect bites.
How does diphenhydramine hydrochloride work?
Diphenhydramine blocks histamine H1 receptors. On the skin this reduces histamine-related itching and inflammation. Oral diphenhydramine enters the brain and causes sedation. Its antimuscarinic activity can cause dry mouth, blurred vision and difficulty passing urine.
diphenhydramine hydrochloride preparations and strengths
How to take diphenhydramine hydrochloride
Follow the product leaflet or prescriber's instructions because oral and topical products are not interchangeable.
Swallow tablets whole with water, with or without food.
Smooth a small amount of cream gently onto affected skin.
Keep cream away from the eyes, mouth, nose, mucous membranes and large or extensively broken areas of skin.
Wash your hands after applying cream unless your hands are being treated.
Check allergy, sleep, cough and cold products to avoid duplicate diphenhydramine.
diphenhydramine hydrochloride side effects
Common or expected effects
- Daytime sleepiness or sedation
- Dry mouth
- Dizziness or unsteadiness
- Difficulty concentrating
- Fatigue
- Increased sensitivity to sunlight with the cream
- Local eczema, burning or rash with the cream
Get urgent medical advice
- Seizure
- Serious allergic reaction with swelling or breathing difficulty
- Fast or irregular heartbeat
- Marked confusion, agitation or hallucinations
- Severe difficulty passing urine
diphenhydramine hydrochloride in pregnancy
Diphenhydramine can be used during pregnancy but is not normally recommended; the selected oral product advises against its use. Discuss treatment and alternatives with a doctor, midwife or pharmacist. Consider the cream only when the expected benefit outweighs potential risk.
diphenhydramine hydrochloride while breastfeeding
The selected oral product advises against use while breastfeeding, although NHS guidance allows oral use when the baby is healthy. Watch for infant sleepiness or poor feeding, and do not share a bed with the baby after taking a sedating antihistamine. Cream is generally compatible with breastfeeding, but prevent contact with treated skin and wash your hands after application.
diphenhydramine hydrochloride interactions
Check all prescription, pharmacy and combination products before using oral diphenhydramine.
Alcohol
Can markedly increase sedation and impairment; avoid alcohol.
Sedatives, sleeping medicines, anxiolytics and opioid painkillers
Additive central nervous system depression may cause pronounced sleepiness and impaired coordination or breathing.
Monoamine oxidase inhibitors
Current or recent use can intensify and prolong antimuscarinic effects; seek professional advice.
Common questions about diphenhydramine hydrochloride
Answers are fully visible for fast scanning and source review.
Can I drive after taking diphenhydramine hydrochloride?
Do not drive if it causes sleepiness, dizziness, blurred vision, poor concentration or impaired coordination. Driving while impaired is unlawful.
Can I use the tablets and cream together?
The selected products advise avoiding other diphenhydramine-containing preparations because combined exposure can increase toxicity and overdose risk.
Sources
These sources were used to prepare and review this medicine page.
Prepared and reviewed by the iatroX editorial team.