How Using the Wrong Flea Meds Can Harm Your Cat

Make the mistake of putting certain DOG flea products on your cat, and you could cause neurologic signs, seizures, coma, even death.

By: alisonpostma
Cats are more sensitive to flea products than dogs. By: alisonpostma

It’s flea and tick time again, folks. Much is written every year about the best products to use for prevention. Controversy abounds about the safety and efficacy of these products.

Today I’d like to talk specifically about cats, and how dangerous certain flea products can be to them.

What’s so special about cats? They are more sensitive to flea products than dogs. It’s a fact.

Many over-the-counter products labeled as safe for cats can still be toxic to some kitties. These products frequently contain pyrethrins. Some cats are more sensitive to these products than others.

Because of owner error, owners mistakenly put certain DOG flea products on their cat, causing neurologic signs, seizures, coma, even death. The dangerous ingredient in these products is permethrin.

Although anyone can make an honest (but serious) mistake, these feline emergencies happen more frequently to folks who don’t see a vet regularly and buy their products at a pet store or a big box store like Walmart. In the confusion of a big, noisy store, they may not shop carefully, and they purchase flea and tick products without any guidance.

Unfortunately, these are also the folks who are least able to afford a veterinary emergency when their cat is dying of a toxic reaction to an OTC flea medication.

But I Would Never Put Dog Stuff on a Cat!

Advantix vs. AdvantageSounds ridiculous, right? There’s a picture of a big dog on the box, so how could anyone put it on their cat?

Well, it happens. Imagine you’re in a dark, overcrowded aisle in a PetSmart or a Walmart. Dogs are barking, kids are screaming, and you’re thinking about getting everything on your list before the kids get home from school.

There are no pimply faced kids in the aisle to give you their “expert” advice, so you throw some flea stuff in your cart. Maybe you pick up stuff for the dog AND the cat.

You get home, throw them in a drawer. The cat is around later that night, and you grab a box and empty the tube on the cat’s neck. You didn’t see the picture of the 80-pound Lab on the box or the tiny cat icon with a diagonal stripe through it hiding somewhere at the bottom.

The next morning, you don’t notice that Nemo isn’t around for breakfast as you rush out the door to get to work. Later that day, after dinner, your husband says the cat food hasn’t been touched. Where’s Nemo?

If Nemo had a product applied to him containing a strong permethrin in it, like a tube of PetsArmorPro or K9 Advantix, Nemo may be unable to walk, seizuring somewhere, or worse.

When a cat has a reaction to a permethrin product, the nervous system is affected. Depending on the dose and the cat, signs can be anything from mild tremors to seizures and coma. Medications are used to control the tremors and seizures, and supportive care is given until the toxin is cleared.

At the first sign of any strange neurologic signs in your cat, please contact your veterinarian immediately.

Why So Many Toxic Mistakes?

  1. Do Not Use On CatsNow that these products are sold just about everywhere — online, at Walmart and Target, in hardware stores, at supermarkets — people are buying them without any supervision or information.
  2. These dog-only products are sold in close proximity to cat products.
  3. Product packaging and names look very similar. K9 Advantix sounds a lot like feline Advantage.
  4. The “DO NOT USE ON CATS” text and icon are not prominent enough on the packaging.
  5. The public is not informed on how toxic these products can be to cats.
  6. There are not enough warning labels and information on most flea and tick pet medications.

There will always be some pets that will have an allergic or idiosyncratic reaction to a product. It’s the same with us. We all make fun of the calm voice on the TV advertisement, warning us of the “sometime serious” side effects of the drug they’re touting. “Dry mouth… swelling of the throat… certain forms of lymphoma… even death has occurred…” Makes you want to run out and beg your doc for a prescription, right?

For many pet medications, the warnings are too few and too general. Now that most of these products are OTC, their patents are expiring, they are made by many different companies and distributed by Walmart and others, the quality of these products is questionable and misuse of these products is more frequent.

In a nutshell, it’s your job to do your research, buy the right products and apply them appropriately. Check with your vet if you bought something OTC and you’re not familiar with the product.

Why Use Anything at All?

I wish fleas and ticks and mosquitoes didn’t exist. I wish they didn’t bite my patients and transmit disease and discomfort. But they do exist, and they are dangerous. So I need to guide my clients about risk versus benefit.

What are the risks of the flea and tick preventives? What are the risks of the insects and diseases they carry? This should be a one-on-one conversation between you and your vet about each of your pets.

When many of these products were introduced, they were handled like a prescription by veterinarians. It was the veterinarian’s job to explain the proper administration, the warnings, check the weight of the animal, etc.

The only permethrin-containing product most vets carry is K9 Advantix, because it is a good choice for certain dogs exposed to heavy burdens of fleas and ticks. But when we take this product from behind the counter and prescribe it for a particular dog, we discuss the product with the client, explain the warnings, ask about cats in the house and so on. It is our responsibility to make sure you use these products appropriately.

Now, you can pick these products off the shelf like toilet paper. But the stakes are far greater if you pick up the wrong flea product instead of the wrong toilet paper. Charmin might be preferred to Cottonelle in some households, but PetArmorPro instead of PetArmor could kill your cat.


This pet health content was written by a veterinarian, Dr. Debora Lichtenberg, VMD. It was reviewed for accuracy by Dr. Pippa Elliott, BVMS, MRCVS, and was last updated Feb. 4, 2019.