Famotidine, sold for people as Pepcid, is an H2-receptor antagonist that reduces the amount of acid the stomach produces. Veterinarians sometimes prescribe it for selected acid-related problems in cats. Using it in cats is off-label, so the medicine, dose, and schedule should come from your veterinarian for your cat, not from the human product label, a dosing table, or a neighbor’s leftover tablets.
What famotidine does and why a vet might prescribe it
Famotidine blocks H2 receptors on cells in the stomach lining, which lowers the acid those cells release. VCA Animal Hospitals lists veterinary uses that include gastrointestinal ulcers, stomach inflammation linked to kidney disease or stress, esophagitis (irritation of the esophagus), and acid reflux. In each case the drug is treating a specific acid-related problem that a veterinarian has identified.
Famotidine does not treat every cause of vomiting. Vomiting can come from diet changes, infections, parasites, pancreatitis, kidney or liver disease, foreign material, and many other conditions, and reducing stomach acid will not fix most of them. If your cat is vomiting repeatedly, or you are tempted to start an acid reducer on your own to see whether it helps, the first step is an exam and a diagnosis.
Forms and how to give it
VCA describes oral famotidine as a tablet or a liquid suspension. Injection is given only in a veterinary hospital. Your veterinarian will tell you which form to use, because tablet strength and liquid concentration are not interchangeable with a dose you have measured in milligrams per kilogram.
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- Timing: VCA advises giving famotidine on an empty stomach, before a meal, when possible.
- If your cat vomits after the dose: VCA says it may be tried again with food or a treat. Ask your veterinarian before repeating a dose, and do not assume a second dose is safe.
- Missed doses: Follow the directions on the prescription label or from your veterinarian. VCA’s general guidance is not to double a dose to make up for a missed one.
The dosage reference, and why it is not your cat’s dose
The Merck Veterinary Manual lists famotidine for dogs and cats at 0.5 to 1 mg/kg by mouth, under the skin, or intravenously, every 12 to 24 hours, in its discussion of gastrointestinal ulcers. The manual’s page does not state a publication year for that passage, so check the current edition before relying on the figures.
This is a clinical reference range for professionals. It is not a recommendation for any individual cat. The correct amount depends on your cat’s body weight, the reason for treatment, the form being used, the route, and the veterinarian’s overall plan. Two practical points follow:
- Do not calculate a dose from a guessed or outdated weight. Ask your veterinarian to weigh your cat and write the dose in milligrams for the specific product you were given.
- Do not assume that a human tablet’s strength tells you how much to give a cat. Strength on a human label is set for people, and dividing a human tablet is not a safe substitute for a prescribed amount unless your veterinarian has told you exactly how to do it.
Possible side effects
VCA lists vomiting, diarrhea, and loss of appetite as possible side effects of famotidine. For injections given in a hospital, VCA also notes low heart rate. Rarely, it reports a low white blood cell count.
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Call your veterinarian if your cat’s appetite drops, if vomiting or diarrhea continues, or if you notice any change in energy or behavior after starting the medicine. Do not stop or change the dose on your own without asking first.
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Who needs extra caution
VCA says famotidine should not be used in a pet with a known allergy to it. It advises caution in several groups:
- Geriatric cats
- Cats with liver, kidney, or heart disease
- Pregnant or nursing cats
If your cat falls into any of these groups, tell your veterinarian before the first dose, because the decision and any dose adjustment depend on the specific condition.
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Medicines and supplements that can interact
VCA’s interaction cautions for famotidine include azole antifungals, cefpodoxime, cefuroxime, cyclosporine, and iron salts. Tell your veterinarian about every medicine, supplement, vitamin, and herbal product your cat receives, including ones you think are harmless or that were bought without a prescription. Do not add, stop, or combine acid-suppressing products on your own.
Overdose and what to do
If you think your cat has received too much famotidine, or has had an unexpected reaction, call your veterinary office immediately, as VCA advises. Do not wait at home to see whether symptoms pass.
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How long treatment lasts
Merck reports that tachyphylaxis, a diminishing response to repeated doses, can occur with continuous famotidine use, and it cites a context of more than 10 days of continuous dosing. This is not a universal stop date. Some cats will be on a short course and others on longer therapy, and the veterinarian sets the length based on the condition and how the cat responds. If your cat’s symptoms seem to return or stop responding, call the veterinarian rather than increasing the dose.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Famotidine compared with proton pump inhibitors
For gastrointestinal ulcers, the Merck Veterinary Manual says proton pump inhibitors such as omeprazole produce more complete inhibition of gastric acid secretion than H2 blockers such as famotidine. It also cautions that combining an H2 blocker with a proton pump inhibitor offers no benefit and may reduce the proton pump inhibitor’s effectiveness.
In practice, this means your veterinarian chooses one approach for a given condition. Whether famotidine, a proton pump inhibitor, or another treatment fits your cat depends on the diagnosis, and changing between them should happen only under veterinary direction.
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When to contact your veterinarian
- Your cat has a known allergy to famotidine or a reaction after a dose.
- Vomiting, diarrhea, or appetite loss continues or worsens.
- You suspect an overdose, a double dose, or an accidental dose of a human product.
- Your cat has not improved, or symptoms come back after the course ends.
- You want to add any new medicine, supplement, or herbal product.
Label information and veterinary references change over time. Confirm the current instructions with your veterinarian and pharmacy when you fill a prescription.
The Bottom Line
Famotidine can be a useful, veterinarian-directed tool for certain acid-related conditions in cats, but the right dose, form, and duration belong to your cat’s diagnosis and your veterinarian’s plan. Never give it based on a dosing table, a human label, or a guess about body weight.
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