Famotidine, widely known by the brand name Pepcid or Pepcid AC, is an H2 receptor antagonist (H2 blocker) that reduces stomach acid production. It is one of the most commonly recommended over-the-counter human medications for use in dogs and cats. Veterinarians frequently recommend famotidine for short-term management of gastric upset, acid reflux, and stomach ulcer prevention, particularly in pets taking medications that can irritate the stomach lining.
While famotidine is available without a prescription at human pharmacies, its use in animals is considered extra-label under AMDUCA and should be directed by a veterinarian. In the United Kingdom, advising OTC human medicines for animals counts as prescribing under RCVS professional guidance. Even for a well-tolerated medication like famotidine, veterinary guidance ensures proper dosing and, importantly, that underlying conditions are not being masked by symptom management.
What Is Famotidine Used For?
Veterinarians may recommend famotidine for:
- Gastric ulcers and erosions — prevention and treatment of stomach ulceration
- Acid reflux (gastroesophageal reflux) — reducing stomach acid that may flow back into the oesophagus
- Nausea and vomiting — particularly when related to excess stomach acid
- Esophagitis — inflammation of the oesophagus, often from acid exposure
- NSAID-induced gastric irritation — protecting the stomach lining in pets taking non-steroidal anti-inflammatory drugs
- Pre-anaesthetic — sometimes given before procedures to reduce the risk of acid reflux during anaesthesia
- Mast cell tumour support — mast cell tumours can release histamine, increasing stomach acid production
Famotidine is typically used as a short-term supportive medication. Chronic vomiting, inappetence, or GI signs warrant a thorough veterinary investigation to identify and treat the underlying cause rather than relying solely on acid reduction.
How Does Famotidine Work?
Famotidine works by blocking histamine H2 receptors on the acid-producing parietal cells of the stomach. Histamine is one of several signals that tell these cells to produce hydrochloric acid. By blocking this particular signal, famotidine reduces the volume and acidity of gastric secretions.
Famotidine is less potent than proton pump inhibitors (PPIs) such as omeprazole, which block the final common pathway of acid production. However, famotidine works faster, with onset of action typically within one hour of oral administration, and effects lasting approximately 12 to 24 hours. For many mild to moderate cases, famotidine provides sufficient acid reduction with a strong safety profile.
Dosage
Your veterinarian will determine the correct dose for your pet. The following is general educational information only.
Dogs
| Dog’s Weight | Typical Dose | Frequency |
|---|---|---|
| 10 lbs (4.5 kg) | 2.5 mg | Every 12-24 hours |
| 20 lbs (9 kg) | 5 mg | Every 12-24 hours |
| 40 lbs (18 kg) | 10 mg | Every 12-24 hours |
| 60 lbs (27 kg) | 15 mg | Every 12-24 hours |
| 80 lbs (36 kg) | 20 mg | Every 12-24 hours |
The commonly cited dose range is 0.25 to 0.5 mg per pound of body weight (0.5 to 1.0 mg/kg), given every 12 to 24 hours. Your veterinarian will select the appropriate dose and frequency based on your dog’s condition.
Cats
| Cat’s Weight | Typical Dose | Frequency |
|---|---|---|
| 5-10 lbs (2.3-4.5 kg) | 2.5 mg (quarter of a 10 mg tablet) | Every 12-24 hours |
| 10-15 lbs (4.5-6.8 kg) | 5 mg (half of a 10 mg tablet) | Every 12-24 hours |
The same dose range of 0.25 to 0.5 mg/lb applies to cats. The standard 10 mg tablet can be split, though this requires some precision. Some owners find it easier to use compounded formulations for cats.
How to Give This Medication
- Use plain famotidine only. Pepcid Complete contains calcium carbonate and magnesium hydroxide in addition to famotidine, which may not be appropriate for all pets. Use the standard Pepcid AC (famotidine only) formulation.
- Tablets are the most common form. Available in 10 mg and 20 mg tablets at most pharmacies.
- Can be given with or without food. Giving on an empty stomach may provide faster onset of acid reduction.
- If you miss a dose, give it as soon as you remember. If it is close to the next scheduled dose, skip the missed dose and continue the regular schedule.
- Do not suddenly stop famotidine after prolonged use without consulting your veterinarian, as rebound acid hypersecretion can occur.
Side Effects
| Common Side Effects | Less Common / Serious Side Effects (Contact Your Vet) |
|---|---|
| Generally very well tolerated | Loss of appetite (rare) |
| Mild lethargy (uncommon) | Vomiting or diarrhoea |
| Dry mouth | |
| Muscle tremors (rare) | |
| Irregular heartbeat (very rare, at high doses) |
Famotidine is considered one of the safest medications used in veterinary medicine. Side effects are uncommon at standard doses. However, if your pet develops new or worsening symptoms while taking famotidine, contact your veterinarian.
Drug Interactions
Inform your veterinarian about all medications and supplements your pet is taking. Potential interactions include:
- Sucralfate (Carafate) — famotidine should be given at least 2 hours apart from sucralfate, as sucralfate requires an acidic environment to activate and famotidine reduces acidity
- Ketoconazole and itraconazole — these antifungals require stomach acid for absorption; famotidine may reduce their effectiveness
- Medications affected by gastric pH — any drug whose absorption depends on stomach acidity may be influenced by famotidine use
- Antacids — concurrent use may reduce famotidine absorption
Contraindications
Famotidine should be used with caution or avoided in:
- Pets with severe kidney disease — famotidine is excreted by the kidneys, and dose reduction may be needed
- Pets with liver disease — dose adjustments may be required
- Known hypersensitivity to famotidine
Storage
- Store at room temperature, 68-77°F (20-25°C).
- Protect from moisture and light.
- Keep out of reach of children and pets.
Cost & Availability
Famotidine is one of the most affordable medications used in veterinary practice.
- Human pharmacy pricing: Generic 10 mg or 20 mg tablets typically cost $4-$10 for 30-90 tablets at major pharmacies
- Store-brand equivalents (Walmart, Costco Kirkland, CVS) are often even cheaper
- Walmart $4 generic list may include famotidine, depending on location
- GoodRx (goodrx.com/pets) may provide additional savings
- No prescription needed to purchase at a human pharmacy, though veterinary consultation is essential before use
The cost savings compared to veterinary-dispensed medications can be significant. A month’s supply from a human pharmacy often costs less than a single vet-dispensed dose pack.
Frequently Asked Questions
Can I give my dog Pepcid for an upset stomach? While famotidine may help if your dog’s stomach upset is related to excess acid, vomiting and nausea have many causes (dietary indiscretion, infections, pancreatitis, foreign bodies, toxin ingestion, organ disease) that famotidine will not address. Contact your veterinarian to determine whether famotidine is appropriate and whether further investigation is needed.
How long can my pet take famotidine? Famotidine is typically used short-term (a few days to a couple of weeks). Longer-term use may be appropriate in certain situations (such as pets with chronic acid-related conditions or those on long-term NSAID therapy), but this should be monitored by your veterinarian. Prolonged acid suppression can affect nutrient absorption and gastric function.
Is famotidine or omeprazole better for my dog? Omeprazole is a more potent acid suppressant than famotidine and is generally preferred for confirmed gastric ulcers or severe acid-related conditions. Famotidine works faster and has fewer drug interactions, making it useful for milder situations. Your veterinarian will determine which is more appropriate.
Can I give my cat Pepcid? Yes, famotidine is used in cats under veterinary direction. The dose is similar on a per-weight basis to dogs. Splitting standard human tablets for accurate cat-sized doses can be challenging; your veterinarian may recommend a compounded formulation for easier administration.