Seresto Flea and Tick Collars and the EPA

An early March 2021 article published in USA Today exposed that the U.S. Environmental Protection Agency (EPA) has received over 75,000 incident reports potentially related to the use of Seresto flea and tick pet collars. Those reports included approximately 1,700 related pet deaths and almost 1,000 involving harm to humans. Seresto was introduced to the market in 2012. The article goes on to accuse the EPA of not alerting the public of the incidents. 

At the time of this post writing, the U.S. House Subcommittee on Economic and Consumer Policy has asked Elanco – the manufacturer of Seresto flea and tick collars – to temporarily recall the product, and has requested documents. Elanco refuses to recall the collars, but will provide the requested information. 

Now, if you have been following Hemopet’s blog, you will know that we have written about flea and tick products in the past. We want to clear up any potential confusion compared to our previous writings, review the veterinary and company pushback, and give our position on the Seresto flea and tick pet collars and the EPA. 


In September 2018, the U.S. Food and Drug Administration (FDA) placed warning labels on certain flea and tick prescription products that are classified as isoxazoline parasiticides and has continued to expand the list. These include:

  • Bravecto (fluralaner) tablets for dogs
  • Bravecto (fluralaner) topical solution for cats and dogs
  • Bravecto Plus (fluralaner and moxidectin) topical solution for cats
  • Bravecto 1-month (fluralaner) tablets for cats
  • Credelio (lotilaner) tablets for dogs and cats
  • Nexgard (afoxalaner) tablets for dogs
  • Simparica (sarolaner) tablets for dogs
  • Simparica Trio (sarolaner, moxidectin and pyrantel) tablets for dogs
  • Revolution Plus (selamectin and sarolaner) topical solution for cats  

The following possible neurological adverse events were noted by the FDA in some dogs and cats: 

  • Muscle tremors
  • Ataxia
  • Seizures

As noted earlier, the USA Today article from March 2021 stated that the EPA received thousands of incident reports regarding adverse events in dogs, cats and humans after the use of non-prescription, over-the-counter Seresto flea and tick pet collars. Some of the anecdotal reports include seizures amongst other adverse reactions. 

So why are these incident reports reported to the EPA and not the FDA?

In general, the EPA regulates pesticides, whereas the FDA regulates parasiticides (antiparasitics). The active ingredients in Seresto collars are flumethrin and imidacloprid, both pesticides. Note, flumethrin is only found in Seresto pet collars. Imidacloprid is indicated to combat fleas and can found in other products. 

The FDA also says another rule of thumb is, “In general, flea and tick products that are given orally or by injection are regulated by FDA.”

Why Seresto flea and tick collars and not other flea and tick collars?

Incident reports regarding other EPA-regulated flea and tick products have been submitted previously that resulted in changes made by the agency. 

For example, the EPA changed labeling and dosing for spot-on flea and tick products based on incident reports in 2009. The EPA also determined that Frontline spot-on treatment cannot be used on rabbits.  

In regards to the lack of response to Seresto incident reports, the USA Today article points to tetrachlorvinphos, another pesticide found in flea and tick collars. After comparing the number of incident reports between tetrachlorvinphos and Seresto, the author found that tetrachlorvinphos had 30 times fewer incidents and 10 times fewer deaths than Seresto, when broken down by year.

Veterinary Pushback and Hemopet Response

A handful of veterinarians and veterinary toxicologists have come forward in defense of the EPA and Elanco. While we at Hemopet understand their position, we respectfully disagree with some of their points.

Veterinary Toxicologists

  • Counterfeit flea and tick products are a big problem. 
  • Anyone can report to the regulatory agencies.
  • The reporting rate of adverse events potentially linked to Seresto collars is only 0.3% of sales since 2012.
  • The incident reports were wide-ranging to not only included seizures, but also liver, kidney and heart failure. Most of the time, veterinarians see a progression of symptoms along the same pathway regarding pesticides and other poisons. 
  • Correlation does not mean causation. Meaning: Just because a pet wears the flea and tick collar, does not mean the collar caused an adverse event.
  • If the EPA thought there were enough similar incidents, the agency would warn the public.

Hemopet Response

The sheer aggregate of incident reports and comparison to other flea and tick collars is staggering. 

True, counterfeit products may be a major factor. However, we do not know yet their extent without an investigation. Plus, if Elanco temporarily pulled Seresto from the market, counterfeit product sales may reduce or increase. In either scenario, we believe the counterfeit products could be a contributor to the cause of the adverse events. 

True, anyone can report and the reporting rate of incidents is low from a percentage standpoint, but again the aggregate is overwhelming. On top of that, we do not know if these incident reports are underreported or overreported. 

Yes; the symptoms listed in the incident reports are all over the map. This is not unusual for regulatory reporting. However, an impartial investigation should be able to distinguish those adverse events not caused by the flea and tick collars from those that truly are product related. 

So, yes, a percentage of the 75,000 reports would be tossed out. That’s to be expected. At the end of the day, companion pet parents would at least know if a sign or symptom is caused by the collar, as well as what sign or symptom is not. 

It is true that correlation does not mean causation according to the strict definitions of “correlation” and “causation”. On the flip side, the cause of an adverse event could be correlated to a Seresto flea and tick collar. To reiterate, we just don’t know without an impartial investigation. Again, the sheer aggregate demands that we find out if an adverse event is caused by a particular flea and tick collar. 

One veterinary toxicologist said we truly would not know a cause and effect without a necropsy. This can be definitive, but again an investigation can still be undertaken to gain more insight.

We have additional questions, of course. Is it the just flumethrin in Seresto flea and tick collars potentially causing adverse events? Is it the combination of flumethrin and imidacloprid? We do not have the answers to those questions. Nobody does. 

Again, we point to the sheer aggregate of incident reports and call on the EPA to launch an impartial investigation.  

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