Famotidine gastric ulcer drug, molecular model. Famotidine inhibits the secretion of stomach acid by blocking H2 receptors on cells in the stomach lining. It is used to treat heartburn, stomach ulcers, gastroesophageal reflux disease and Zollinger-Ellison syndrome. Atoms are represented as spheres and are colour-coded: carbon (grey), hydrogen (white), oxygen (red), nitrogen (blue) and sulphur (yellow).