DIPHENHYDRAMINE

synthetic drug used to counteract the histamine reaction, as in allergies. Introduced into medicine in 1945 and marketed under several proprietary names, including Benadryl, it is administered orally or by intramuscular or intravenous injection in the form of its hydrochloride. It has been used to control the symptoms of hay fever, acute skin reactions (such as hives), and contact dermatitis (such as from poison ivy). The most common side effect is drowsiness. Diphenhydramine hydrochloride occurs as white crystals, soluble in water. It is available in capsules and in solution for injection.