The Canine Ledger

Flea and Tick Tablets and Seizures: What the FDA Warning Means

The FDA warns that one class of flea and tick drugs can cause tremors and seizures in some dogs. What the warning says, how rare it seems, and what to ask.

Written by thecanineledger

This page carries no advertising, and nothing on it is for sale.

If your dog has a seizure that lasts more than five minutes, or has one seizure after another without waking fully in between, this is an emergency. Go to a vet now. A 2024 consensus statement from the American College of Veterinary Internal Medicine, following the international definition, describes status epilepticus, the dangerous continuous form, as “any prolonged seizure lasting >5 minutes” (Charalambous et al., J Vet Intern Med 2024). → Is This an Emergency? How to Tell, and What to Do First

The US Food and Drug Administration has a standing warning about one class of flea and tick drugs. Its fact sheet says: “The FDA is alerting pet owners and veterinarians of the potential for neurologic adverse events in dogs and cats when treated with drugs that are in the isoxazoline class” (FDA, Fact Sheet for Pet Owners and Veterinarians about Potential Adverse Events Associated with Isoxazoline Flea and Tick Products).

The same page also says the drugs remain approved: “The FDA considers products in the isoxazoline class to be safe and effective for dogs and cats”.

Both statements are true together. While these drugs can and do cause neurological problems in a small number of dogs, most dogs take them without trouble, and fleas and ticks carry real diseases of their own. This page explains the warning, what is and isn’t known about how often it happens, and what to discuss with your vet.

1. What isoxazolines are

Isoxazolines are a class of drugs that kill fleas and ticks. Most are given as a chewable tablet, usually monthly or every few months; some are applied to the skin. They are widely used in Canada, the US and the UK.

We don’t name brands here. Your vet can tell you whether a product they prescribe is in this class, and the FDA’s fact sheet lists the ones approved in the US.

2. What the FDA warning says

The fact sheet describes the problem: “Isoxazoline products have been associated with neurologic adverse reactions, including muscle tremors, ataxia, and seizures in some dogs and cats”. Ataxia means wobbliness or loss of coordination.

Two points in the warning matter most to owners:

It is uncommon. “Although most dogs and cats haven’t had neurologic adverse reactions, seizures may occur in animals without a prior history”.

It is a conversation, not a ban. The FDA says that “pet owners should consult with their veterinarian to review their patients’ medical histories and determine whether a product in the isoxazoline class is appropriate for their pet.”

Our note: The FDA page is US-only. We haven’t read the Canadian, UK or European regulators’ statements.

3. How often does it happen?

This is the question owners most want answered, and we couldn’t find a reliable answer.

Reports to regulators count problems that someone noticed and reported. They don’t say how many doses were given in total, so they can’t give a rate. A review of the research in 2026 summed up the position: “Controlled studies generally demonstrate wide safety margins; however, post-marketing pharmacovigilance has identified rare but sometimes serious neurological adverse events, particularly in predisposed animals or in the context of impaired efflux transport, such as ABCB1/MDR1 mutations or P-glycoprotein inhibition” (Markowska-Buńka, Rasiński & Ziółkowski, Int J Parasitol Drugs Drug Resist 2026).

In plain terms: in testing before approval the drugs were well tolerated, but after millions of doses, rare serious reactions have turned up, more often in dogs who were already at risk.

A survey to read with care. A 2018 online survey of owners and vets, published in 2020, collected 2,751 responses and reported serious problems including seizures and death (Palmieri et al., Vet Med Sci 2020). Among respondents whose dog had any flea treatment, “AE were reported for 66.6% of respondents” (AE means adverse events). That figure says more about who answered than about the drugs: people chose to take part, and people whose dog had a bad reaction are far more likely to respond. A survey like this can show that reactions happen. It can’t show how common they are.

Our note: We give no percentage or rate, because we didn’t find a reliable incidence figure.

4. Dogs who may be at higher risk

Dogs with a history of seizures. The FDA’s advice to review a dog’s medical history with the vet matters most here. Tell your vet if your dog has ever had a seizure, even once.

Dogs with the MDR1 (ABCB1) gene change. This gene change, common in collies, Australian shepherds and some related herding breeds, affects how the body clears some drugs. The 2026 review names it as a factor.

Dogs on certain other medicines. The review also names “P-glycoprotein inhibition”, which some other drugs can cause. Give your vet a full list of everything your dog takes, including supplements.

Our note: That collies, Australian shepherds and related herding breeds often carry MDR1 is general knowledge, not from a source we read for this page. Whether MDR1 is linked to these reactions isn’t settled.

5. If you think your dog has had a reaction

  • A seizure lasting more than five minutes, or repeated seizures, is an emergency. Go to a vet now.
  • Trembling, wobbliness or a single short seizure: phone your vet the same day.
  • Note the time you gave the dose and when the signs started. Keep the packaging.
  • Don’t give another dose until you have spoken to your vet.

The FDA’s advice is the same: “If your dog or cat experiences any adverse event while using an isoxazoline product, first consult your veterinarian.” Reactions can also be reported to the regulator and the manufacturer; how depends on where you live.

Our note: This advice is ours. If you’re unsure about a seizure, treat it as urgent and call your vet.

6. Weighing it up

Fleas and ticks aren’t harmless. Ticks can carry serious diseases, and which ones depends on where you live. Stopping prevention altogether carries risks of its own.

The choice is between products, and between the risk of a rare drug reaction and the risk of the diseases prevention protects against. There are flea and tick products in other drug classes. Each has its own side effects. Your vet knows which parasites are common where you live and your dog’s history, and can weigh it with you.

Questions to ask:

  • Is this product in the isoxazoline class?
  • Does my dog’s history make another class a better choice?
  • Should my dog be tested for MDR1?
  • Which parasites are the real risk here, and in which months?

Our note: Other drug classes exist. We don’t name them. Ask your vet about alternatives.

7. What we could not verify

Commonly saidWhat we found
“Flea tablets cause seizures”In some dogs. The FDA says reactions include “muscle tremors, ataxia, and seizures in some dogs and cats”, and that most dogs haven’t had them.
“The FDA has banned them” or “recalled them”No. The FDA “considers products in the isoxazoline class to be safe and effective”.
A percentage risk of seizuresNot found. Reports and surveys don’t give a reliable rate.
“Only dogs with epilepsy are at risk”No. The FDA says seizures may occur “in animals without a prior history”.
Canadian and UK regulator positionsNot read.

Sources

Always confirm with your vet before acting on anything on this page.