When I was a little girl, my family had a cat named Suki. I loved the animal shelter more than I did visiting the zoo, and I picked Suki out myself.
Back in the 80s, we didn’t have spot-on flea treatments or any of the other advances in flea control we do today. What we had were flea collars and flea dips you had to bathe your dog or cat in. We also had whole-house foggers that would spew chemicals into the furthest corners of your home, hoping to kill off all of the fleas.
Living in north Florida, we didn’t have the kind of harsh winter that killed off all the fleas like you get in some parts of the country, so fleas were a real problem. When Suki and our dog at the time had a persistent flea infestation, they were both subjected to frequently repeated flea dips to try to get it under control.
One Sunday morning when I was eleven years old, Suki threw up her breakfast. That’s not so unusual for a cat. But what was unusual was that a while later she started convulsing and wouldn’t stop. It went on and on, and it was terrible.
My mother sent my sister and me off to Sunday school with a carpool ride, and she went to the vet. I couldn’t concentrate on anything anyone was saying that morning. I just wanted to know how my beloved cat was. Suki never came home, and I never saw her again even to say goodbye.
Fast forward 30 years or so, and I read a description of permethrin poisoning in cats from flea products. It brought the awful scene from that Sunday morning flooding back. I had the sinking realization permethrin, found in flea dips, had killed Suki.
Permethrin Toxicity
Many flea solutions contain the pyrethrins, an insecticide with an active ingredient permethrin. This is a synthetic form of a naturally occurring extract from the Tanacetum cinerariifolium flower, part of the chrysanthemum family.
But instead of being a flower, permethrin is a neurotoxicant. It kills fleas by over-exciting their nerves.
Unfortunately, cats are especially sensitive to permeterhins because they can’t metabolize them quickly enough. As a result, permethrin is the most common cause of poisoning of cats in the US. They can cause neurological symptoms like tremors, seizures, and hypersalivation. In some cases, they can even cause death.
Permethrin has been eliminated from most products labeled for cats, though you may still find it today as an ingredient in flea dips labeled for use for both cats and dogs. Products are allowed to be labeled for use in cats when they contain low levels of permethrin. To be safe, always use a product specifically labeled as safe for cats, and avoid pyrethrin and permethrin ingredients.
Cats can be exposed to permethrin by being given a flea product labeled for dogs, or by spending time in close contact with a dog who has had a topical flea product applied. They can also be exposed to it when it is used in insectisides for the garden.
There is no antidote for permethrin/pyrethrin poisoning in cats. Treatment is limited to removing as much of the toxin from the skin as possible to prevent absorbing more and to supportive care.
Questionable Internet Flea Treatment Advice
Today, with the convenience of the internet, it’s easy to reach out to others who love the same things we do for advice and support. As a result, I am often among groups of animal lovers online. Far too often, I see people giving the advice that you can save money on cat flea control by buying a big dog flea medication then splitting the dose up among many cats.
When I see this, I try to warn that it is dangerous, pointing out permethrin poisoning is a risk if you don’t know what is in the dog flea treatment. Answers have ranged from “I’m in rescue and I know what I’m doing” to “I have done it plenty of times and nothing bad has ever happened.” I don’t want to argue with people on the internet, but I don’t want to stand by and watch cats be killed like my Suki, either.
Recently, I have started leaving Facebook groups when this issue comes up because I don’t have the heart to have the same argument over and over again. Even if the person who asked the question reads my warning, the next person who skims past trying to find a quick answer won’t, and I can’t stand to see the tragic results show up in the group later.
A Safer Flea Treatment Plan
If you need to use a flea product for your cat, consider a bath with a few drops of Dawn dish soap, which is often used on kittens too young for flea chemicals. If you use a chemical flea treatment, make sure it’s a flea product labeled for cats and doesn’t contain permethrin. If you are at all unsure about the product, ask your veterinarian about their experience with it.
Also, make sure you know how much your cat weighs. Flea treatment is generally applied by weight, and you can overdose a cat if you guess their weight wrong. Your vet will be happy to set up a weigh-in for your cat if you don’t have an appropriate scale, possibly even at no charge.
Keep your cat safe and happy this flea season!
Research and further reading
Journal of the American Veterinary Medical Association, Toxicosis in cats erroneously treated with 45 to 65% permethrin products.
Journal of Feline Medical Surgery, Feline permethrin toxicity: retrospective study of 42 cases.

Flea treatments are scary! My human is super careful about what we get.
That was very important information, thanks!
Thanks for sharing this important information. Flea treatments can be scary if not the right one or used correctly.
Excellent article. I had never heard of permethrin before. We have a multi-species home and I would never think to use a dog product on our cats, or the other way around. I can see why you’d have a hard time staying in certain FB groups. Thank you for sharing this important information!
that is so horrible….and yes, getting medical advise from the internet is definitely not ok.
How very sad that you lost your Suki to this poison. We are very fortunate in that we’ve only encountered a flea problem once, when Sophie came to live with us after surviving on the street for who knows how long. At any rate, we wound up with a real infestation problem with both her and Eddie (my only two cats at the time), but our combat included baths with (human) shampoo and constant combing. Many people don’t know that fleas will drown in just about anything except plain water (something has to break the surface tension). Once when I found a flea on myself and was nowhere near one of the water-with-a-drop-of-shampoo stations I had all over the place, I managed to kill the stupid thing in a bit of spit. Unconventional, but it worked.
Oh, and I avoided the poisonous stuff because of my sensitivity to products like that but later learned how very bad it was from our vet.
Thank you. Excellent advice and I can’t read some of the cat forums and other pet related forums. because of things like this.
That’s very important information ! Great reminder, and great advice for cat people who were not aware of this yet. Purrs
Thank you for this very, very important information! My Mom told us we lost a cousin to one of those horrible over-the-counter flea sprays years and years ago and it gets her all up in a tizzy whenever she sees someone online asking which flea spray to buy for their cats. She can’t say NO strongly enough! Thank you!
I am so sorry about Suki.
I have also seen permethrin in an anti-insect etc. spray applied to human clothing.
In general, I would suggest either get your flea treatment from your vet, or ask them for a recommendation.
This is a pet peeve of our vet tech friend. I’ve been unfortunately enough to watch some of the videos she posts on her FB page of cats that are brought in the the clinic where she works after they’ve had dog flea products used on them. It’s horrible. They’ve managed to save a few but it’s a sight you can’t unsee.
What a horrific story. I can see why that experience has stayed with you all your life. I’m thankful that here in Vermont flea meds aren’t particularly necessary for indoor cats. Angel Tara had a bad outbreak over a decade ago that required their use, but I haven’t had to use any since.
Thanks for this info, and we’re so sorry about Suki. Our mom doesn’t give us flea treatments, and wonders if she should. it can be so scary.
I am so sorry about what happened to Suki. Thank you for warning people about this. How sad that it is still on the market.
NO, NO AND NO AGAIN!!,, Never give cats drugs/treatments that are meant for dogs! They are not the same. I would never give my cat something that I wasn’t sure wouldn’t hurt them. I’ve had a couple of my cats killed by toxins outside but I will never know for sure what it was. But when your baby comes crying at you with blood coming from their mouths you know they were poisoned somehow. Whether they drank anti-freeze or ate the wrong plant, we will never know. All I know is my cats stay inside and I don’t accept flowers as gifts. Flowers are pretty but some are poisonous to animals.
Humans must really be very careful in treating fleas. We read some scary things out there.
I absolutely agree with you, if you do not know what is in the product you are using you should not take a large dog flea product and apply it to cats.
However..
Frontline plus, Advantage (regular only), and Revolution are all very safe to split up. The rep from Frontline once told the staff at the clinic i worked at that if a cat was larger than average it would be beneficial to them to use the small dog size because it is the exact same product. These are the only “dog” flea products I would ever suggest you use on your cat, and I would highly suggest you not buy them online or over the counter but only from your vet so you can be sure you are not getting a counterfeit product.
Getting medical information on the internet is risky. If you don’t know the source and why they are saying what they are saying you can’t know if their advice is legitimate or third hand information. Being in rescue of neonatal kittens, and also in a group for diabetic cats, we often see vets who give advice that is harmful because they don’t deal with the issue on a regular basis. I would say you should always ask your vet about info you find on the internet, but I know first hand that many vets are so skeptical of anything on the internet that they roll their eyes and stop listening after you say you found it on the internet – regardless of your source.
Never stop telling people that they shouldn’t use dog products on cats if they don’t know what they are doing and you don’t know or trust who you are talking to.