Famotidine, sold under the brand name Pepcid among others, is a histamine H₂ receptor antagonist medication that decreases stomach acid production. It is used to treat peptic ulcer disease, gastroesophageal reflux disease, and Zollinger-Ellison syndrome. It is taken by mouth or by injection into a vein. It begins working within an hour.

Common side effects include headache, intestinal upset, and dizziness. Serious side effects may include pneumonia and seizures. Use in pregnancy appears safe but has not been well studied while use during breastfeeding is not recommended.

Famotidine was patented in 1979 and came into medical use in 1985. It is available as a generic medication. In 2020, it was the 66th most commonly prescribed medication in the United States, with more than 10 million prescriptions.