Get emergency medical help if you have any of these signs of an allergic reaction to famotidine: hives; difficult breathing; swelling of your face, lips, tongue, or throat.
Stop using famotidine and call your doctor at once if you have:
fast or pounding heartbeats with severe dizziness; or
unexplained muscle pain, tenderness, or weakness especially if you also have fever, unusual tiredness, and dark colored urine.
Common famotidine side effects may include:
headache;
dizziness; or
constipation or diarrhea.
This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.