Medicines that reduce the amount of acid the stomach produces. Histamine2 (h2) signals the stomach to make acid. Examples of h2 blockers include cimetidine, famotidine, nizatidine, and ranitidine. (Brand names: tagamet, pepcid, axid, zantac. ) They are used to treat ulcer symptoms. Nonprescription h2 blockers are zantac 75, axid ar, pepcid-ac, and tagamet-hb.