Diphenhydramine
AllergyAlso known as Benadryl
Diphenhydramine is a first-generation antihistamine. It blocks histamine like the newer allergy pills, but it also crosses into your brain, which is why it makes most people seriously drowsy. That's not a side effect you can shrug off — it's strong enough that diphenhydramine is the main ingredient in most over-the-counter sleep aids. For everyday allergies, newer non-drowsy options are usually a better choice; this one is more of a short-term, at-home medicine.
How to take it
When
It works within about 30 minutes and the drowsiness can last for hours — even into the next morning. Plan around that.
Food
With or without food. Taking it with food can ease a queasy stomach.
Avoid
Never drive after taking it. Don't mix it with alcohol, sleep aids, or other sedating medicines. Adults 65 and older should generally avoid it — it raises the risk of confusion and falls.
Watch for doubling up
Diphenhydramine hides in many products — Benadryl, ZzzQuil, and 'PM' versions of pain relievers. Check labels so you don't take it twice without realizing.
Missed a dose?
This is an as-needed medicine, so there's no missed dose to worry about. Just don't take doses closer together than the label allows, and never double up.
Common side effects
- Strong drowsiness
- Dry mouth, nose, and throat
- Dizziness
- Constipation
- Trouble urinating
Call a doctor if
- Trouble breathing, or swelling of your face, lips, or tongue — call emergency services now. Diphenhydramine is NOT a substitute for epinephrine — a severe allergic reaction needs an epinephrine injection and emergency care, even if you've taken a Benadryl.
- Confusion, hallucinations, or extreme agitation — get emergency help, especially in an older adult
- Seizure or fainting — call emergency services
- Fast or irregular heartbeat
- Unable to urinate at all