Cimetidine (Tagamet®), Ranitidine (Zantac®), and Famotidine (Pepcid®)

Cimetidine (Tagamet®), Ranitidine (Zantac®), and Famotidine (Pepcid®)


Cimetidine, ranitidine, and famotidine are related medicines.   They are in a class of drugs called H2 blockers.  They have similar effects and uses in veterinary medicine.

H2 blockers cause decreased production of stomach acid.   In pets, these medicines are prescribed mainly to treat or prevent gastrointestinal upset (vomiting, diarrhea, or lack of appetite).  They also may be used to prevent or treat ulcers or irritation of the esophagus, stomach, or intestines.


H2 blockers are readily available as oral tablets.  Liquid suspensions are often available. Some pharmacies may be able to prepare palatable liquid suspensions or pills.

Veterinarians frequently administer injectable forms of H2 blockers to patients.

Side Effects

Side effects from orally administered cimetidine, ranitidine, and famotidine are very rare. H2 blockers are among the safest classes of drugs used in veterinary medicine.

The very few pets that develop side effects to H2 blockers may show disorientation, mental confusion, or skin rashes.  Gastrointestinal upset is an extremely rare side effect of H2 blockers.  In humans, H2 blockers have been linked in rare occasions to blood cell problems.

Pets that receive H2 blockers by injection may suffer pain at the injection site.


Veterinarians may recommend periodic blood and urine tests for animals that take H2 blockers regularly over extended periods of time.

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The contents of this page are provided for general informational purposes only. Under no circumstances should this page be substituted for professional consultation with a veterinarian.