Cetirizine, or Reactine, is an antihistamine used to alleviate symptoms of an allergic reaction. When an allergic reaction occurs the immune system produces a substance called histamine which in turn produces all the symptoms (congestion, difficulty breathing, itching, sneezing, watery eyes) of an allergic reaction. Antihistamines are a class of drugs that prevent allergic reactions by binding to histamine receptors and preventing histamine from being registered by the body. Common side effects of antihistamines include drowsiness, loss of concentration, dry mouth and upset stomach. People with stomach ulcers, lung problems, high blood pressure and pregnancy should not take antihistamines without consulting a physician.
