Used primarily to treat and prevent stomach and duodenal ulcers by reducing gastric acid production. It works by blocking histamine H2 receptors in the stomach, which helps heal erosive esophagitis and manages gastroesophageal reflux disease (GERD). Also used short-term to relieve heartburn and acid indigestion. In some cases, it is employed off-label to treat certain skin conditions related to histamine activity and as an adjunct in anaphylaxis management. Additionally, cimetidine has been studied for its potential immune-modulating effects and investigated in cancer therapy support due to its influence on suppressor T-cell activity.