# Famotidine for Cats: Side Effects and Vomiting Relief Famotidine for cats side effects are usually mild when a veterinarian sets the dose, but the drug is not right for every cat and it is not a cure for vomiting. It reduces stomach acid, which helps with some stomach problems, yet vomiting in cats has many possible causes, some of them serious [1]. This article is educational and is not a substitute for veterinary diagnosis or treatment. ## Quick Answer - Famotidine is an H2 blocker that lowers stomach acid. It is not a general anti-vomiting drug, so it only helps when excess acid is part of the problem. - A veterinarian decides the dose from your cat's weight and health. In one study of healthy cats, doses ranged from 0.5 to 1.24 mg/kg, with a median of 0.87 mg/kg given by mouth twice daily [2]. - Side effects are uncommon and usually mild, but injectable famotidine given into a vein has been linked to a small drop in red blood cell counts in hospitalized cats [3]. - Giving famotidine every day for two weeks may make it work less well over time, based on what happens in cats and dogs [2][4]. - Vomiting that repeats, comes with lethargy, or lasts more than a day needs a veterinary exam, not a home remedy [1]. ## What Famotidine Is and What Veterinarians Use It For Famotidine is an acid-reducing medication from the class called H2 blockers. You may know it by a human brand name, but veterinarians prescribe it for cats too. It comes as an oral tablet, an oral liquid, and an injectable form. Veterinarians reach for famotidine when they suspect stomach acid is irritating the stomach lining or making nausea worse. Common situations include gastritis, stomach ulcers, and reflux. It is also sometimes used in cats with kidney disease or liver disease, where stomach irritation and vomiting often go together [1]. Here is the part owners often miss. Famotidine is not an anti-nausea drug in the way that some other medications are. A systematic review of antiemetic strategies in cats found that maropitant, a different drug, reduced vomiting risk in controlled studies [5]. Famotidine works on acid, not on the brain's vomiting center. If your cat is vomiting because of motion, pain, kidney failure, or a foreign object, famotidine will not fix it. That is why a veterinarian needs to see your cat before you reach for any acid reducer. Vomiting can come from digestive disease, kidney or liver failure, pancreatitis, nervous system problems, poisons, parasites, infections, medications, swallowed objects, food allergies, or tumors [1]. Some of those causes are emergencies. If your cat is vomiting and you are not sure whether a medication is to blame, this guide on [medication-related vomiting in cats](/knowledge/veterinary-medicine/pet-medication-guide/cat-medication-vomiting-when-worry) can help you sort out what to watch for. ## How Famotidine Works in Cats Famotidine blocks histamine H2 receptors on the acid-producing cells in the stomach. When histamine cannot dock at those receptors, the cells release less acid. Less acid means less irritation to the stomach lining and often less nausea tied to that irritation. The effect is real but not permanent. In healthy cats given famotidine by mouth twice daily, the drug raised stomach pH during the first days of treatment [2]. Stomach pH is a measure of acidity, and higher numbers mean less acid. The catch is what happens with long-term use. In the same cat study, the effect on stomach pH weakened over time when the drug was given twice daily for 14 days [2]. A similar pattern shows up in dogs, where repeated famotidine administration led to a significant drop in its acid-suppressing effect by day 13 compared with day 1 [4]. This is called tolerance, and it is one reason veterinarians do not keep every cat on famotidine forever. ## Famotidine Cats Dose: Who Decides and How It Is Given Never guess the dose. Your veterinarian calculates it from your cat's weight, diagnosis, and other medications. Cats are small, and a tablet made for a person can be far too much. For context, the dose used in a controlled study of healthy cats was 0.5 to 1.24 mg/kg by mouth, with a median of 0.87 mg/kg, given twice daily [2]. That is a research range, not a prescription for your cat. Your veterinarian may choose a different amount or schedule based on what is wrong. ### Giving the medication - Give it exactly as prescribed, with or without food as your veterinarian directs. - If you use a liquid, measure with the syringe or dropper provided, not a kitchen spoon. - If you use a tablet, do not crush or split it unless your veterinarian says it is fine. - Keep a simple log of times and doses. It helps your veterinarian adjust treatment. ### If you miss a dose Give the missed dose when you remember, unless it is almost time for the next one. In that case, skip the missed dose and go back to your normal schedule. Do not double up to catch up. Call your veterinarian if you are unsure. ### If your cat vomits the dose Do not give a second dose without asking. Your cat may have absorbed some of it, and repeating the dose could lead to too much medication. Call your veterinarian for guidance. ## Famotidine for Cats Side Effects Most cats tolerate famotidine well. When problems happen, they tend to be mild and short-lived. The table below covers what owners most often ask about. | Side effect | How common or serious | What to do | |---|---|---| | Mild stomach upset, soft stool, or appetite change | Uncommon and usually mild | Note it and mention it at your next visit. Call if it lasts more than a day or two. | | Drop in red blood cell count (anemia) after intravenous use | Uncommon but serious enough to monitor. In hospitalized cats, the median drop in packed cell volume was 3 to 4 percent, and it was no different between cats that received famotidine by vein or under the skin and those that did not [3] | This is a hospital setting concern. Your veterinary team monitors blood counts. Ask about the route if your cat is hospitalized. | | Drowsiness or unusual calm | Uncommon | Keep your cat quiet and watch for improvement. Call if your cat seems weak or hard to rouse. | | Reduced drug effect over time with daily use | Expected with repeated dosing. The acid-suppressing effect weakened over 14 days in cats [2] and in dogs [4] | Tell your veterinarian if vomiting returns while your cat is still on the medication. | | Signs of an allergic reaction such as facial swelling, hives, or trouble breathing | Rare | Stop the medication and seek emergency care right away. | A few points deserve a closer look. The anemia concern comes from injectable famotidine, not the pill. A review of 142 hospitalized cats found that famotidine given intravenously was not linked to a clinically significant drop in packed cell volume when it was given slowly [3]. Some veterinarians still prefer the under-the-skin route for cats, and that is a reasonable choice to discuss with your care team. The tolerance issue is easy to overlook at home. If your cat seemed better on day two and worse on day twelve, that does not mean the drug stopped working for no reason. It may mean the body adapted [2][4]. Your veterinarian may switch to a different acid reducer or change the plan. If your cat is on other medications, side effects can overlap and be hard to sort out. This article on [gabapentin side effects in cats](/knowledge/veterinary-medicine/pet-medication-guide/gabapentin-side-effects-cats) explains how to tell medication effects apart from other problems. ## Who Should Not Take Famotidine and What Interacts With It Famotidine is not for every cat. Your veterinarian may avoid it or use it with extra caution if your cat has: - Kidney disease, because the drug is cleared by the kidneys and dosing may need adjustment - Liver disease, because drug processing can change - A known allergy to famotidine or similar drugs - A stomach or intestinal blockage, which needs a different treatment entirely - Severe or unexplained vomiting that has not been diagnosed [1] Drug interactions matter too. Acid reducers can change how well other medications are absorbed, and some drugs affect how famotidine is cleared from the body. Tell your veterinarian about everything your cat takes, including prescription drugs, over-the-counter products, and supplements. Do not start famotidine on your own if your cat is already on another acid reducer. If your cat is being treated for a urinary problem, some of the same medication-safety rules apply. This overview of [urinary tract infection side effects in cats](/knowledge/veterinary-medicine/clinical-methods/cat-urinary-tract-infection-side-effects) covers what to watch for when cats are on treatment. ## Overdose and When to Call for Help If your cat swallowed more famotidine than prescribed, call for help right away. Do not wait for symptoms. Call your veterinarian or an animal poison control hotline immediately if: - Your cat ate several tablets or drank a large amount of liquid - Your cat is vomiting repeatedly, drooling heavily, or seems disoriented - Your cat collapses, breathes oddly, or has a seizure - You are not sure how much was swallowed Bring the medication bottle with you or have it nearby. The label tells the responder the strength and the number of tablets, which speeds up treatment. For a single missed dose or a mild upset stomach, a phone call to your regular veterinarian during business hours is usually enough. For a suspected overdose, treat it as an emergency. ## Limitations and When to Contact a Veterinarian Famotidine treats acid. It does not treat the cause of most vomiting. That is the biggest limitation, and it is why home treatment can delay real care. Call your veterinarian the same day if your cat: - Vomits more than two or three times in a day - Vomits for more than 24 hours - Has frequent hairballs along with vomiting [1] - Refuses food or water - Seems painful when you touch the belly Go to an emergency clinic now if your cat: - Vomits blood or material that looks like coffee grounds - Has a swollen, hard, or painful abdomen - Is weak, wobbly, or cannot stand - Breathes fast or with effort - May have eaten a poison, a string, a toy, or another object [1] - Is a kitten or a senior cat with sudden vomiting Schedule a routine visit if your cat vomits off and on for weeks, loses weight, or has a change in appetite or energy. Chronic vomiting often has a treatable cause, and finding it early makes a difference. Vomiting is not the same as regurgitation. Regurgitation is passive, with no retching or belly contractions, and the food often comes up undigested in a tube shape [1]. If that sounds like your cat, tell your veterinarian, because the workup is different. Every cat is an individual. Only a veterinarian who examines your cat can decide whether famotidine is safe and appropriate. ## Frequently Asked Questions ### Is famotidine safe for cats? Famotidine is generally safe for cats when a veterinarian prescribes it at the right dose for that cat. Side effects are uncommon and usually mild. The main cautions are the small anemia risk with intravenous use in hospitalized cats [3] and the loss of effect with daily use over about two weeks [2][4]. ### Can I give my cat famotidine for vomiting? Only if your veterinarian tells you to. Famotidine lowers stomach acid, so it may help when acid irritation is part of the problem, but it does not stop vomiting from most other causes. Vomiting can signal kidney failure, pancreatitis, a swallowed object, or a poison, and those need diagnosis and different treatment [1]. ### How long does famotidine take to work in cats? The acid-suppressing effect starts within the first days of treatment in healthy cats [2]. If your cat is not improving within a day or two, or is getting worse, stop guessing and call your veterinarian. Waiting longer can let a serious problem grow. ### Can famotidine stop working over time? Yes. In healthy cats given famotidine twice daily for 14 days, the effect on stomach pH weakened over time [2]. The same pattern appears in dogs by day 13 of repeated dosing [4]. If vomiting returns while your cat is still taking the medication, your veterinarian may change the plan. ### What should I do if my cat vomits after taking famotidine? Do not give another dose. Call your veterinarian and describe how soon after the dose the vomiting happened and what it looked like. If your cat also seems weak, drools heavily, or has trouble breathing, treat it as an emergency and go to a clinic right away. ## Related Articles - [What Are the Side Effects of Apoquel for Cats?](/knowledge/veterinary-medicine/pet-medication-guide/apoquel-side-effects-cats) - [Is Your Cat's Medication Causing Vomiting? When to Worry](/knowledge/veterinary-medicine/pet-medication-guide/cat-medication-vomiting-when-worry) - [Cat Urinary Tract Infection Side Effects](/knowledge/veterinary-medicine/clinical-methods/cat-urinary-tract-infection-side-effects) - [What Are the Side Effects of Gabapentin for Cats?](/knowledge/veterinary-medicine/pet-medication-guide/gabapentin-side-effects-cats) - [Cat Allergy Medication Side Effects: What to Watch For](/knowledge/veterinary-medicine/skin-allergy-and-ear-care/cat-allergy-medication-side-effects) - [Famotidine H2 Blocker Dose: Gastric Acid Reduction Guide Dogs Cats](/knowledge/veterinary-medicine/calculators-clinical-tools/famotidine-h2-blocker-dose-gastric-acid-reduction-guide-dogs-cats) - [Pepcid for Cats Side Effects and Vomiting Use](/knowledge/veterinary-medicine/pet-medication-guide/pepcid-for-cats-side-effects) - [Famotidine for Cats: Dosage and Safe Use](/knowledge/veterinary-medicine/pet-medication-guide/famotidine-for-cats-dosage) - [Famotidine for Cats With Kidney Disease: Safe or Not?](/knowledge/veterinary-medicine/senior-and-chronic-care/famotidine-cats-kidney-disease) ## References 1. [Vomiting in Cats - Cat Owners](https://www.merckvetmanual.com/cat-owners/digestive-disorders-of-cats/vomiting-in-cats). Merck Veterinary Manual. 2. [The frequency of oral famotidine administration influences its effect on gastric pH in cats over time](https://pubmed.ncbi.nlm.nih.gov/30746763/). Journal of veterinary internal medicine, 2019. 3. [Risk of hemolytic anemia with intravenous administration of famotidine to hospitalized cats](https://pubmed.ncbi.nlm.nih.gov/18371027/). Journal of veterinary internal medicine, 2008. 4. [Repeated Famotidine Administration Results in a Diminished Effect on Intragastric pH in Dogs](https://pubmed.ncbi.nlm.nih.gov/27906465/). Journal of veterinary internal medicine, 2017. 5. [Receptor-Targeted Antiemetic Strategies in Cats: A Systematic Review and Intervention-Specific Meta-Analysis](https://pubmed.ncbi.nlm.nih.gov/42599757/). Veterinary medicine and science, 2026. ## Further Reading - [American Veterinary Medical Association: First Aid Tips for Pet Owners](https://www.avma.org/resources-tools/pet-owners/emergencycare/first-aid-tips-pet-owners) - [Merck Veterinary Manual: Cat Owners](https://www.merckvetmanual.com/cat-owners) - [Cornell Feline Health Center: Health Information](https://www.vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center/health-information)