Permethrin toxicity in cats


  • Permethrin is a chemical used to treat fleas. It’s safe to use on dogs but high doses are extremely poisonous for cats.
  • Common symptoms of permethrin poisoning include drooling, twitching and having seizures.
  • Left untreated, permethrin poisoning is usually fatal.
  • Contact your vet immediately if you’ve accidentally put a dog flea treatment on your cat or if your cat is showing signs of permethrin poisoning/toxicity

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. It’s also 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 symptoms include:

If your cat is showing any of the above symptoms, contact your vet for an appointment straight away – left untreated, permethrin poisoning can be fatal.


Your vet will treat your cat for permethrin toxicity/poisoning based on their history (if they have been in contact with a product containing permethrin) and also their symptoms.


If your cat has had contact with permethrin, wash it off immediately using warm water and dilute washing up liquid (if they will allow you to) and call your vet straight away. It’s likely that your cat will need to be admitted for treatment. Treatment may include:

  • Washing off any remaining permethrin from the skin and coat.
  • Anti-seizure medication if they are having seizures.
  • Medication to stop the permethrin causing further damage.
  • A fluid drip to keep your cat hydrated.


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, it's best to avoid using permethrin flea treatments for any dog in the same house. If you do choose to use a product containing permethrin, make sure your cat does not come into contact with it, or lick it off your dog for 72 hours after application. Always read instructions and warnings carefully before using any flea treatment on your pet.

There are cat flea collars containing low doses of permethrin available to buy, which have been classified as safe by the Veterinary Medicines Directorate (VMD). As with any medications, there is always a risk of side effects and some individuals may be more sensitive than others. If your cat shows sensitivity even at low doses these products should be avoided.

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, always contact your vet if you’re concerned.


Treatment for a cat with permethrin toxicity can become very expensive, so it’s important to speak openly with your vet about the cost of treatment, your finances, and what you think is right for your cat.

Consider insuring your cat as soon as you get them, before any signs of illness start to ensure you have financial support to care for them.


Why is permethrin toxic to cats and not toxic to dogs?

Cats don’t have the protein needed to help break down permethrin in the body, as a result it builds up and causes toxicity/poisoning.

Why are there flea collars for cats available to buy that have permethrin in them?

The Veterinary Medicines Directorate ensures all veterinary medicines have gone through safety checks. It has deemed certain cat collars containing permethrin safe for use in cats, as they contain very low doses of permethrin. Our vets recommend reading instructions and warning labels of all medicines very carefully before use. If you aren’t sure about a product, contact your vet for advice before using it.

Can I use just a small amount of my dog’s spot-on flea treatment that has permethrin in it?

No, spot-on treatments are very concentrated and contain high levels of permethrin. So, even a small amount of dog flea treatment containing permethrin is likely to cause toxicity in your cat.

Can I use flea spray for my house that has permethrin in it?

Yes, it is safe to use flea spray containing permethrin to kill fleas in the environment as you are not directly applying this to your cat. You should always remove all animals from the area before starting treatment, leave the area vacant for half an hour after spraying and then ventilate the room (by opening windows and doors) for at least an hour before allowing any pets back into the area.

If my pet has a reaction to a flea treatment, where can I report it?

Anyone (including you, your vet or vet nurse) can report a reaction to a veterinary medicine to the Veterinary Medicines Directorate. If you have the product’s packaging in front of you, you will have all the necessary information to hand, including the batch number.

How do I safely buy flea treatment for my cat online?

To reduce the risk of harming your pet by using potentially unsafe treatments, you are encouraged to buy from websites that the VMD has inspected. These websites display a VMD logo.

Published December 2023

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