It is a human medicine. A vet may still prescribe it for a dog or cat, which is legal and common, but it means no company has proved to the FDA that it works or is safe in that animal, and there is no approved animal dose to look up. Ask your vet what they expect it to do and what to watch for.
The label says, word for word:
Human label: "PEPCID tablets are indicated in adult and pediatric patients 40 kg and greater for the treatment of: active duodenal ulcer (DU). active gastric ulcer (GU). symptomatic nonerosive gastresophageal reflux disease (GERD). erosive esophagitis due to GERD, diagnosed by biopsy." There is no animal label for famotidine.
PEPCID is contraindicated in patients with a history of serious hypersensitivity reactions (e.g., anaphylaxis) to famotidine or other histamine-2 (H2) receptor antagonists.
Central nervous system (CNS) adverse reactions, including confusion, delirium, hallucinations, disorientation, agitation, seizures, and lethargy, have been reported in elderly patients and patients with moderate and severe renal impairment treated with PEPCID.
In adults, symptomatic response to therapy with PEPCID does not preclude the presence of gastric malignancy.
OTC Pepcid AC Drug Facts, Do not use: "if you have trouble or pain swallowing food, vomiting with blood, or bloody or black stools"; "with other acid reducers".
Every approved medicine has a field study behind it, and the label prints what happened:
Human label: "The most common adverse reactions are: headache, dizziness, constipation, and diarrhea."
Human drug only; no animal label exists (DailyMed famotidine results, 436 in total, are all human prescription or OTC products). Veterinarians may prescribe it extra-label under AMDUCA (https://www.fda.gov/animal-veterinary/resources-you/ins-and-outs-extra-label-drug-use-animals-resource-veterinarians). Prescription PEPCID label: Initial U.S. Approval: 1986; revised 6/2024; additional adult indications, verbatim: "treatment of pathological hypersecretory conditions (e.g., Zollinger-Ellison syndrome, multiple endocrine neoplasias). reduction of the risk of duodenal ulcer recurrence."
The emergency page sorts the signs by how long you have, and the symptom checker asks what you are seeing. Reactions to a medicine can also be reported to the FDA yourself: how to report a problem.
These answers come from the approved label on DailyMed, read on 2 October 2026. Where the label does not say, the answer says so, and the vet or the pharmacist is the one to ask.
The approved use is quoted at the top of this page. The label read for these answers is the one for Pepcid tablets, a human prescription medicine that lowers the acid the stomach makes: it is approved for ulcers and acid reflux disease in people and does not mention dogs or cats, so ask the vet what it has been prescribed for in your pet. Pepcid AC, the tablet sold over the counter, has a label of its own, which is in the sources below.
The label gives no time for a pet. In people, it says the effect on stomach acid began within one hour of a dose by mouth and was greatest within one to three hours. Ask the vet what to expect and by when.
The label gives doses for people only, so the amount and the timing for your pet come from the vet. It says the tablets may be taken with or without food, and that they may be given with antacids.
The label does not say what to do about a missed dose. Call the clinic or the pharmacy before you give the next one.
The warnings on the label are quoted above. This label is written for people. It tells patients to report confusion, agitation, seizures or lethargy to a healthcare provider immediately, and it names older patients and patients with kidney problems as the ones at risk. The label has nothing on dogs or cats, so ask the vet what to watch for and when to call.
The label says to store the tablets at 77°F, and it allows 59° to 86°F. It says they belong in a tightly closed container that keeps out light.
The FDA says the best way to get rid of most unused or expired medicines is a take-back option: a drug take-back location, which can be at a pharmacy or a police station, or a prepaid mail-back envelope. If you cannot use one and the medicine is not on the FDA's flush list, the FDA says to mix it, uncrushed, with something unappealing such as dirt, cat litter or used coffee grounds and to seal the mixture in a plastic bag before throwing it away. Flushing is only for medicines on that list, such as opioids. Do not give leftovers to another pet.
Write the dose, the times and the stop date here, then print this page for the fridge.
Dose and times: _____________________________________________
Stop date: _____________________________________________