Antihistamine, << `an` tee HIHS tuh meen, >> is the name of a group of drugs used to treat symptoms of allergies. These symptoms include irritated eyes, runny nose, sneezing, and hives. Antihistamine drugs work by counteracting the effects of histamine, a substance found in many body cells. Excessive or inappropriate release of histamine into body fluids can cause allergies such as hay fever and contribute to dangerous reactions to insect bites and certain medications. Antihistamines are also used to treat motion sickness.
Chemists working in France developed the first useful antihistamines in the early 1940’s. Diphenhydramine, a common antihistamine drug, was developed in the United States in 1946. People can purchase diphenhydramine, known by such trade names as AllerMax and Benadryl, and many other antihistamines without a doctor’s prescription. Nonprescription antihistamines are sold to promote sleep and relieve cold symptoms, as well as to treat allergies.
A common side effect of many antihistamines is drowsiness. For this reason, people are advised not to drive or operate heavy machinery while using the drugs. In the 1970’s and 1980’s, scientists developed the first antihistamines that did not cause drowsiness. The first such drug available in the United States was terfenadine, sold until 1998 under the trade name Seldane. A similar drug, astemizole, was sold under the name Hismanal until 1999. In rare cases, these drugs have caused irregular heartbeats. Newer antihistamines, including fexofenadine, marketed under the name Allegra, do not cause such side effects. Many antihistamines are available only with a doctor’s prescription, but others are sold over the counter.
