diphenhydramine, Benadryl

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GENERIC NAME: diphenhydramine

BRAND NAME: Benadryl, Sominex, Unisom, Nytol, and several others

DRUG CLASS AND MECHANISM: Diphenhydramine is an antihistamine used for treating allergic reactions. Histamine is released by the body during several types of allergic reactions and--to a lesser extent--during some viral infections, such as the common cold. When histamine binds to receptors on cells, it stimulates changes within the cells that lead to the release of chemicals that cause sneezing, itching, and increased mucus production. Antihistamines compete with histamine for cell receptors and bind to the receptors without stimulating the cells. In addition, they prevent histamine from binding and stimulating the cells. Diphenhydramine also blocks the action of acetylcholine (anticholinergic effect) and is used as a sedative because it causes drowsiness. The FDA originally approved diphenhydramine in 1946.

PRESCRIBED FOR: Diphenhydramine is used for the relief of nasal and non-nasal symptoms of various allergic conditions such as seasonal allergic rhinitis (hay fever). It also is used to alleviate cold symptoms and hives (chronic urticaria). Although antihistamines are the preferred class of drugs in allergic rhinitis, they only reduce symptoms by 40% to 60%. Diphenhydramine also is used for allergic reactions involving the eyes (allergic conjunctivitis), to prevent or treat active motion sickness, and for mild cases of Parkinsonism, including drug-induced Parkinsonism. The last two uses (motion sickness and Parkinsonism) are based on the anticholinergic effects of diphenhydramine, and not its antihistamine effects. Diphenhydramine also is used for treating insomnia.

Medically Reviewed by a Doctor on 3/27/2015

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