Diphenhydramine (Benadryl)

Photograph of Diphenhydramine (Benadryl) under the microscope.

Diphenhydramine is one of many antihistamine agents that has both drying and sedative effects that is used to combat the symptoms of hay fever and other types of allergy. These agents work primarily be blocking the effects of histamine, which causes itching, sneezing, runny nose, and watery eyes. Histamine can also close bronchial tubes and make breathing difficult. Single doses are absorbed quickly and most activity is completed in one hour with distribution throughout the entire body. Most of the drug is found as a degradation product in the liver, though little is excreted in the urine. Diphenhydramine is most commonly used as an antihistaminic agent, for antiparkinsonism, and for motion sickness. Side effects include fast or irregular heartbeat, sore throat, fever, drowsiness, and cotton mouth.

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