Side effects of taking famotidine tablets include constipation, headaches and diarrhea, according to WebMD. Serious side effects include fast, slow or irregular heartbeat; seizures; and easy bleeding and bruising. Persistent sore throat, confusion, fever, hallucinations and depression are additional severe side effects.
Signs of a serious allergic reaction include the development of a rash as well as itching and swelling of the face, tongue and throat, advises WebMD. Individuals who experience such symptoms should seek medical help right away.
Famotidine is an H2 blocker that reduces stomach acid levels, explains WebMD. The medication treats and prevents heartburn, acid indigestion and other symptoms caused by excess stomach acid.