Used to reduce stomach acid production, primarily in the treatment of peptic ulcers, gastroesophageal reflux disease (GERD), and Zollinger-Ellison syndrome. It helps heal ulcers and relieves symptoms such as heartburn and indigestion. Also used preventatively in hospitalized patients at risk of stress ulcers and during anesthesia to prevent acid aspiration. Works by blocking histamine H2 receptors in the stomach lining.