Permethrin toxicity in cats


  • Permethrin is a chemical used to treat fleas. It’s safe to use on dogs but is extremely poisonous for cats.
  • Common symptoms of permethrin poisoning include drooling, acting strangely, twitching and fitting.
  • Left untreated, permethrin poisoning is usually fatal.
  • Contact your vet immediately if your cat has been exposed to permethrin or if you’ve accidentally put a dog flea treatment on your cat.

What is permethrin and why is it dangerous?

Permethrin is an insecticide used to kill fleas. It’s safe to use on dogs, but is extremely poisonous for cats. Permethrin is found in a number of different flea products for dogs, including spot-on treatments, shampoos, sprays and flea collars and is a common ingredient in household flea sprays and powders.

Permethrin is highly toxic to cats, it affects their nervous system, first causing it to become over sensitive (twitching/seizures) and then causing paralysis.

Permethrin poisoning is most common when a dog flea treatment is put on a cat by accident, but can also happen if a cat comes into contact with permethrin on a dog, for example when grooming or sharing a bed.


Permethrin is absorbed very quickly so signs of poisoning usually appear within a few hours (but can take up to 36 hours). Common signs include:

When to contact your vet

Contact your vet immediately for an emergency appointment, if you think your cat may have come into contact with permethrin.

You know your cat best. If they don’t have the symptoms listed above but you are still concerned it’s always best to contact your vet.


It is important to get help for your cat as soon as possible because left untreated, permethrin poisoning can be fatal. If your cat has had contact with permethrin, wash it off immediately (using warm soapy water) then call your vet. It’s likely that your cat will need to be admitted into the veterinary hospital for treatment. Treatment is likely include:

  • Medication to control fits
  • Medication to stop the permethrin causing further damage
  • Washing off any remaining permethrin from the skin and coat
  • A fluid drip to give your cat intravenous fluids.


Cases of permethrin poisoning that are caught early, and treated quickly tend to have a good outlook. Sadly, cats with more severe symptoms such as twitching and seizures often have a worse outlook.


  • Never use a dog flea treatment on your cat.
  • If you own a cat, avoid any flea products that contain permethrin even for use on your dog.


Treatment for a cat with permethrin toxicity can be very expensive; hospitalisation can cost hundreds of pounds. It’s important to speak openly to your vet about your finances, the cost of treatment, as well as what you think is right for your cat.

Find out whether you are eligible for free or low cost PDSA veterinary treatment using our checker.

Consider insurance for your cat as soon as you get them, to make sure you have the support you need if they become unwell.

Published@ April 2020

Written by vets and vet nurses. This advice is for UK pets only. Illustrations by Samantha Elmhurst.