Cimetidine 400mg Tablet is an antacid. It reduces the amount of acid produced by your stomach. It is used to treat and prevent heartburn, indigestion and other symptoms caused by too much acid in the stomach. It is also used to treat and prevent stomach ulcers, reflux disease and some other rare conditions. Cimetidine must be swallowed whole with water preferably before meals to prevent the symptoms of acidity.