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 its receptors on cells, it stimulates changes within the cells that lead to sneezing, itching, and increased mucus production. Antihistamines compete with histamine for cell receptors; however, when they bind to the receptors they do not stimulate 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.
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