An H2-receptor antagonist drug used in the treatment of DUODENAL ULCER by reducing the hyperacidity of the gastric juice. The drugs block the production of HISTAMINE produced by MAST CELLS in the stomach lining. Histamine stimulates the acid-secreting cells in the stomach. Ranitidine, like other H2-blocking drugs, is used in combination with an antibiotic to treat ulcers caused by HELICOBACTER PYLORI.