Flea and Tick Medicine Poisoning in Cats

It can cause symptoms such as over-excitability and constant trembling.

Cats can get sick from flea and tick medicine. By: kwc909
Cats can get sick from flea and tick medicine. By: kwc909

Pyrethrin is a naturally occurring substance found in chrysanthemum plants and is effective at killing insects.

Once extracted, it is used in flea-killing products, but it has been largely replaced by a synthetic version called pyrethroid. Both substances act similarly and carry the risk of toxicity if a cat licks and swallows flea product applied to the fur.

Pyrethroid drugs cause nerves to fire off continually; cats with this toxicity are overexcited, shake and tremble to the point of exhaustion.


Signs of poisoning tend to develop within 1 to 3 days of the cat swallowing pyrethrin.

The first signs are something like:

  • Excessive twitching of a paw
  • Heavy salivation
  • Possibly vomiting

The cat shivers and shakes uncontrollably and is overly excitable. The tremors can be so severe that the cat eventually collapses from exhaustion.

Some cats are unusually sensitive to pyrethrin, even at low doses, and applying it to the skin may even cause an allergic reaction. This allergy is not usually life-threatening, but the skin becomes hot, red and itchy. The cat then scratches and can break the skin’s surface and induce infection.


Poisoning occurs when the cat licks the pesticide off his fur following application of a pyrethroid-containing product.

The substance alters the transmission of sodium ions in the channels of the nerve and interferes with nerve transmission. This has the effect of constantly stimulating the nerves, which then tell muscles to contract repeatedly. Hence, the symptoms of muscle twitching, hyper-excitability and tremors.


It may be impossible to make a definite diagnosis based on lab tests. While in theory it is possible to detect the presence of pyrethroid in samples of liver or brain, collecting those samples for analysis creates more problems than it solves.

A decision to treat for pyrethroid toxicity is usually made based on a recent history of contact with flea products and the signs the cat is showing. Many of the poisons that cats most commonly encounter are treated in broadly the same way and so reaching a precise diagnosis is not critical to the eventual outcome.


There is no specific antidote for pyrethroid toxicity; treatment is largely aimed at controlling the muscle tremors, preventing further absorption of the toxin and supportive care while the cat gets better.

If the cat has eaten pyrethroid within the past 2 hours, your veterinarian may suggest making him vomit to empty his stomach.

Activated charcoal given by mouth also helps mop up any pyrethroid left in the gut and stops it from being absorbed. Other than that, the cat may need to go on an intravenous drip to stop dehydration if he is too wobbly to eat or drink.

If caught early and treatment started promptly, most cats make a full recovery from pyrethroid poisoning.


Be careful when using pyrethroid-containing products on the cat. Always stick to the dosage instructions and apply the drops sufficiently high up on the neck so the cat cannot lick it off.

If you have more than 1 cat in the house, it is a good idea to separate the cats during treatment so they cannot lick each other.


  • “Properties and applications of pyrethoids.” Elliott. Environ Health Prospect, 14.
  • Small Animal Formulary. Tennant. Publisher: BSAVA Publications.


This pet health content was written by a veterinarian.

Dr. Pippa Elliott, BVMS, MRCVS

View posts by Dr. Pippa Elliott, BVMS, MRCVS
Dr. Pippa Elliott, BVMS, MRCVS, is a veterinarian with nearly 30 years of experience in companion animal practice. Dr. Elliott earned her Bachelor of Veterinary Medicine and Surgery from the University of Glasgow. She was also designated a Member of the Royal College of Veterinary Surgeons. Married with 2 grown-up kids, Dr. Elliott has a naughty puggle called Poggle, 3 cats and a bearded dragon.

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