# Can Cats Have Ivermectin for Worms? Safety and Dosage Can cats have ivermectin for worms? Yes, but only under veterinary direction. Ivermectin is a real prescription dewormer used in cats, and it can be safe when the dose is calculated for your cat's weight and the right product is chosen. The danger is that ivermectin has a narrow margin in cats, and giving the wrong amount or a product made for another animal can cause neurological poisoning. This article is educational and is not a substitute for veterinary diagnosis or treatment. ## Quick Answer - Ivermectin is a broad-spectrum antiparasitic drug used in both animals and people, and it is effective against several worm and parasite species [1]. - Cats can receive ivermectin, but the dose must be calculated by a veterinarian based on your cat's weight, health, and the parasite being treated. - Never give your cat ivermectin products labeled for dogs, livestock, or humans. Species and formulation matter, and some products are not safe for cats. - Signs of ivermectin poisoning are mostly neurological and can start within 4 to 12 hours after ingestion, though some signs take 2 to 3 days to appear [2]. - If you suspect your cat ate ivermectin or is acting strangely after a dose, call your veterinarian or a pet poison hotline right away. Do not wait for symptoms to worsen. ## What Ivermectin Is and What Veterinarians Use It For Ivermectin belongs to a drug family called macrocyclic lactones. These drugs kill parasites by interfering with their nervous system, and they are used against a wide range of worms and external parasites in veterinary medicine [1]. In cats, veterinarians may use ivermectin or related drugs to treat certain internal parasites and some external parasites, depending on the diagnosis. Ivermectin is also used in combination products. One field study evaluated a topical product combining ivermectin, imidacloprid, and praziquantel in 142 naturally infested cats and found it effective for flea control under routine clinical conditions [3]. That tells you ivermectin can be part of a legitimate, veterinarian-guided parasite plan for cats. It does not mean you can grab any ivermectin product off a shelf and apply it. The word "dewormer" covers a lot of ground. Different worms need different drugs, and some products treat only one type of parasite. If you are not sure what your cat has, start with [Deworming Medicine For Cats](/knowledge/veterinary-medicine/parasitic-diseases/deworming-medicine-for-cats) to understand the options before you give anything. ## How Ivermectin Works Ivermectin opens channels in the nerve and muscle cells of parasites. This paralyzes and kills susceptible parasites. The drug is effective against many nematodes (roundworms) and some other parasites [1]. The reason ivermectin can be risky in cats is that the drug also affects the mammal nervous system when it reaches high enough levels. Normally, a pump called P-glycoprotein keeps ivermectin out of the brain. Cats with a mutation in the MDR1 gene (also called ABCB1) have a faulty version of this pump, so the drug builds up in the central nervous system and causes toxicity [4][5]. This is why two cats of the same weight can respond very differently to the same dose. One cat may be fine, and another may develop severe neurological signs. A genetic test can identify cats with this mutation, and it is one reason veterinarians are cautious with macrocyclic lactones in cats [4]. ## Dosing Basics for Cats ### Who decides the dose Your veterinarian decides the dose. There is no safe home dose you can calculate on your own. The veterinarian considers your cat's weight, age, health conditions, other medications, and the specific parasite being treated. Doses are not interchangeable between species, and a dose that is safe for a dog can be toxic to a cat. ### How it is given Ivermectin can be given orally, topically, or by injection, depending on the product [1]. Your veterinarian will tell you which route and which product to use. Follow the label and the prescription exactly. Do not split, double, or guess at a dose. Some ivermectin products are sold for livestock or for dogs, and those are not appropriate for cats. If you have ivermectin at home for another animal, keep it locked away from your cat. ### What to do about a missed dose If you miss a dose, do not give a double dose to catch up. Call your veterinarian and ask how to proceed. For most parasite preventives, giving the next dose at the normal time is fine, but your veterinarian will confirm based on the product and the reason your cat is taking it. If you are managing other cat medications at home, it helps to know which human drugs are dangerous. [Can Cats Have Tylenol?](/knowledge/veterinary-medicine/toxicology-and-food-safety/can-cats-have-tylenol) explains one of the most common and most dangerous mistakes owners make. ## Side Effects of Ivermectin in Cats Most cats tolerate ivermectin at the correct dose with few problems. When side effects happen, they are usually neurological because that is where this drug causes trouble in sensitive cats [6][4]. | Side effect | How common or serious | What to do | |---|---|---| | Mild lethargy or sleepiness | Uncommon at correct doses, usually mild | Monitor your cat. Call your vet if it lasts more than a day or gets worse. | | Drooling, vomiting, or not eating | Possible, can be early sign of toxicity | Call your veterinarian the same day. | | Dilated pupils (mydriasis) | Typical sign of macrocyclic lactone toxicosis in cats [4] | Treat as an emergency. Call your vet or poison control now. | | Wobbling, weakness, or trouble walking (ataxia) | Typical sign of toxicosis, can progress [4] | Emergency. Do not wait. | | Tremors, seizures, or coma | Severe neurotoxicity, reported in real-world cases [6] | Emergency. Go to a veterinary hospital immediately. | | Tongue weakness (glossal paresis) | Characteristic of eprinomectin toxicosis in cats, may affect eating [4] | Emergency. Your cat may need nutritional support that bypasses the mouth. | Signs of ivermectin poisoning usually begin within 4 to 12 hours after ingestion, but some can take 2 to 3 days to show up [2]. If your cat received a dose and is acting off, do not assume it will pass. Early treatment matters. ## Who Should Not Take Ivermectin Cats with a known MDR1 (ABCB1) mutation should not receive ivermectin or related macrocyclic lactones. Cats with liver or kidney disease, very young kittens, and cats that are already weak or debilitated need extra caution, and your veterinarian will decide whether the benefit outweighs the risk. Drug interactions matter too. Drugs that are central nervous system depressants or that are themselves P-glycoprotein substrates can worsen or prolong toxicosis and should be avoided in a cat being treated with these products [4]. Tell your veterinarian about every medication, supplement, and topical product your cat receives, including flea treatments and anything you bought without a prescription. If you are considering an over-the-counter product for your cat, check whether it is safe first. [Can You Give Your Cat Benadryl? Dosage and Safety Guide](/knowledge/veterinary-medicine/pet-medication-guide/cat-benadryl-dosage-safety) and [Can I Give My Cat Melatonin? Safety, Dosage, and When to Avoid It](/knowledge/veterinary-medicine/vet-visit-decisions/can-i-give-my-cat-melatonin) cover two common owner questions about cat-safe medications. ## Overdose and When to Call for Help Ivermectin toxicity in cats is a medical emergency. There is no antidote for macrocyclic lactone toxicosis, and treatment is supportive care, which may include intravenous fluids, seizure control, and nutritional support if your cat cannot eat normally [4]. The sooner treatment starts, the better the chance of recovery. Call your veterinarian or a pet poison hotline immediately if: - You gave more ivermectin than prescribed. - Your cat licked or ate a product meant for a dog or livestock. - Your cat has dilated pupils, wobbling, weakness, tremors, or seizures. - Your cat is drooling, vomiting, or refusing food after a dose. - You are not sure what your cat got into. Do not try to make your cat vomit unless a veterinarian tells you to. Do not give activated charcoal or any other home remedy. Bring the product packaging with you to the clinic so the veterinarian knows exactly what was given and how much. ## Limitations and When to Contact a Veterinarian Ivermectin is not a one-size-fits-all dewormer, and cats are more sensitive to it than many other species. Some cats carry a genetic mutation that makes normal doses dangerous, and there is no way to know without testing or a careful veterinary history [4][5]. A topical product that is safe for one cat may not be safe for another. Contact your veterinarian the same day if your cat has mild lethargy, vomiting, drooling, or a poor appetite after receiving ivermectin. Go to an emergency clinic immediately if you see dilated pupils, wobbling, weakness, tremors, seizures, or trouble swallowing. Schedule a routine visit if you need a deworming plan, want to discuss parasite prevention, or are unsure whether a product you already have is safe for your cat. Every cat is different. Your veterinarian needs to examine your cat and review the full picture before recommending any dose or product. ## Frequently Asked Questions ### Can I give my cat ivermectin for worms without a prescription? No. Ivermectin for cats should only be given under veterinary direction. The dose depends on your cat's weight, health, and the parasite being treated, and the wrong amount can cause serious neurological toxicity. ### What happens if my cat gets too much ivermectin? Too much ivermectin can cause neurological signs such as dilated pupils, wobbling, weakness, tremors, and seizures. There is no antidote, so treatment is supportive and must start as soon as possible [4]. ### Are some cats more sensitive to ivermectin than others? Yes. Cats with a mutation in the MDR1 (ABCB1) gene have a faulty P-glycoprotein pump, so ivermectin builds up in the brain and causes toxicity even at label doses [4][5]. A genetic test can identify these cats. ### Can ivermectin treat ear mites in cats? Ivermectin has been used for some external parasites in cats, but ear mites are usually treated with products specifically labeled for that purpose. Ask your veterinarian which product is safest for your cat. For more on this topic, see [Ivermectin Cat Ear Mites](/knowledge/veterinary-medicine/parasitic-diseases/ivermectin-cat-ear-mites). ### How long after a dose would signs of toxicity show up? Signs can begin within 4 to 12 hours after ingestion, but some develop more slowly and may take 2 to 3 days to appear [2]. If your cat is acting normally for the first few hours, keep watching for at least a couple of days. ## Related Articles - [Can You Give Your Cat Benadryl? Dosage and Safety Guide](/knowledge/veterinary-medicine/pet-medication-guide/cat-benadryl-dosage-safety) - [Deworming Medicine For Cats](/knowledge/veterinary-medicine/parasitic-diseases/deworming-medicine-for-cats) - [Can Cats Have Tylenol?](/knowledge/veterinary-medicine/toxicology-and-food-safety/can-cats-have-tylenol) - [Can I Give My Cat Melatonin? Safety, Dosage, and When to Avoid It](/knowledge/veterinary-medicine/vet-visit-decisions/can-i-give-my-cat-melatonin) - [Ivermectin Cat Ear Mites](/knowledge/veterinary-medicine/parasitic-diseases/ivermectin-cat-ear-mites) - [Tapeworm Medicine For Cats](/knowledge/veterinary-medicine/parasitic-diseases/tapeworm-medicine-for-cats) - [Ivermectin for Cats: Dosage, Safety and Alternatives](/knowledge/veterinary-medicine/pet-medication-guide/ivermectin-cats-dosage) - [Ivermectin for Cats: Fleas, Mange and Safety Questions](/knowledge/veterinary-medicine/pet-medication-guide/ivermectin-cats-fleas-mange) - [Milbemycin and Ivermectin for Cats: What to Know](/knowledge/veterinary-medicine/pet-medication-guide/milbemycin-ivermectin-cats) - [Toxocara cati Roundworm Infection in Cats and Kittens: Prenatal Transmission and Clinical Management](/knowledge/parasites/pet-parasites/toxocara-cati-roundworm-cats-kittens-prenatal-transmission) - [Taenia taeniaeformis Tapeworm Infection in Cats: Rodent Intermediate Host and Clinical Management](/knowledge/parasites/pet-parasites/taenia-taeniaeformis-cats-rodent-tapeworm-intermediate-host) ## References 1. [Therapeutic and Formulation Advances of Ivermectin in Veterinary and Human Medicine](https://pubmed.ncbi.nlm.nih.gov/41304722/). Pharmaceutics, 2025. 2. [Understanding the Symptoms and](https://www.petpoisonhelpline.com/uncategorized/understanding-the-symptoms-and-treatment-for-ivermectin-sensitive-dogs/). Pet Poison Helpline. 3. [Field evaluation of a topical combination of ivermectin, imidacloprid, and praziquantel for flea control in cats under routine clinical](https://pubmed.ncbi.nlm.nih.gov/41822165/). Frontiers in parasitology, 2026. 4. [Management of Eprinomectin Neurotoxicosis in Cats](https://pubmed.ncbi.nlm.nih.gov/42750103/). Journal of veterinary emergency and critical care (San Antonio, Tex. : 2001), 2026. 5. [Avermectin-induced neurotoxicity and mortality reported more commonly in cats homozygous for ABCB11930_1931del TC after application of eprinomectin- versus selamectin-containing products](https://pubmed.ncbi.nlm.nih.gov/40738165/). Journal of the American Veterinary Medical Association, 2025. 6. [Ivermectin Toxicity in Humans and Animals: Clinical Spectrum, Mechanisms, and Management](https://pubmed.ncbi.nlm.nih.gov/41837342/). Journal of applied toxicology : JAT, 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)