Possible side effects from famotidine include:

fatigue
insomnia
muscle pain
vomiting 

Tell your doctor if any of these symptoms are severe or do not go away:

dizziness
headache
diarrhea
nausea
constipation 

If you experience any of the following symptoms, call your doctor immediately:

allergic reaction (difficulty breathing; closing of the throat; swelling of the lips, tongue, or face; or hives)
easy or unusual bruising or bleeding
bleeding gums
irregular heartbeat
yellowing of the skin or eyes
a rash

Side effects other than those listed here may also occur. Please talk to your doctor about any side effect that seems unusual or that is especially bothersome.

 

FDA Information

Why is this medication prescribed?

Other uses for this medicine

Dosage and using this medicine

What special precautions should I follow?

What should I do if I forget a dose?

What storage conditions are needed for this medicine?

In case of an emergency/overdose