Antihistamine
Antihistamine is any drug that blocks the action of histamine . Antihistamines are used primarily to control symptoms of allergic conditions such as hay fever . They alleviate runny nose and sneezing and, to a lesser extent, minimize conjunctivitis and breathing difficulties. Antihistamines can also alleviate itching and rash caused by food allergy. Chemically, antihistamines comprise several classes, and a person who does not obtain relief from one type may benefit from another. Side effects of these drugs can include drowsiness, loss of concentration, and dizziness. People taking antihistamines should not drink alcoholic beverages or perform tasks requiring mental alertness, such as driving. A few antihistamines, such as terfenadine and astemizole, are nonsedating. Although antihistamines are included in many over-the-counter cold remedies, their usefulness in such preparations is questionable. Antihistamines may relieve symptoms of allergy accompanying a cold, or they may have an