Famotidine is used to treat ulcers of stomach, intestines and to prevent intestinal ulcers from coming back after they have healed. This medication is also used to treat certain problem (such as erosive esophagitis, gastroesophageal reflux disease-GERD, Zollinger-Ellison syndrome). It works by decreasing the amount of acid your stomach makes. Famotidine belongs to a class of drugs known as H2 blockers. CAS ID: