How it works

Benadryl is a brand (trade) name for diphenhydramine, an antihistamine that can be used to treat allergies, motion sickness, help induce sleep, and relieve Parkinson's disease symptoms.

Diphenhydramine works by blocking histamine-1 (H1) receptors to treat allergic reactions. This prevents histamine from acting on the airways, blood vessels, and gastrointestinal tract, reversing symptoms like bronchoconstriction (airway narrowing), rash and itching, and stomach cramps. Diphenhydramine also inhibits serotonin reuptake and blocks acetylcholine receptors and sodium channels, among other things. These latter effects are responsible for its sedative properties as well as side effects like dry mouth.

Benadryl belongs to the first-generation antihistamine class of medications. Benadryl belongs to the ethanolamine class of antihistamines.