Seresto Pet Flea and Tick Collars Still on the Market but with Mitigation Measures

Seresto pet flea and tick collars were implicated for possibly causing almost 1,700 companion pet deaths for almost 10 years in 2021. This placed a much-needed spotlight on the regulatory agency, U.S. Environmental Protection Agency (EPA), that apparently had sat on the data.

The expos by Investigative Midwest’s intrepid journalist, Johnathan Hettinger, caused an outcry from companion pet parents and environmentalists who were subsequently also alarmed that the EPA would not initiate a recall. On top of that, the product’s manufacturer (Elanco) held fast and refused to withdraw the collars from the market even after public pressure. Congress even became involved and demanded a recall but to no avail.

Skipping forward to 2023, the EPA analyzed the data, decided not to pull the collars off the market, and imposed mitigation measures.

During that 2-year period of time, Hettinger continued regularly to chronicle the journey to the EPA’s decision. We provide links to several of his articles below.

For this post, we will be concentrating on narratives.

Key Takeaway

Per the EPA’s memorandum:

“During the review of the reported cases of potential deaths associated with the collar the Agency found that critical details of incidents were often missing from case narratives, often preventing the Agency from determining the cause of the incident. Where sufficient details were provided, there were no cases where high confidence existed in a correlation between the collar use and the death, often due to confounding factors such as concurrent medical conditions.”


That is alarming because by November 7, 2022, Hettinger stated that more than 100,000 Seresto incidents had been reported involving both companion pets and humans.

Did the EPA’s 2023 memorandum provide some statistics? Yes; from but based on a subset of the data.

Of the 1,477 companion dog and cat death cases reviewed, it was determined 4 cases for canine and 9 cases for feline were found to be probably or definitely related to the collar. These cases were associated with mechanical strangulation or trauma caused by the collar, rather than from the active ingredients contained in the collar.

The most common clinical adverse event reported for companion dogs was itchy skin. Regarding cats, application site hair change was the most reported adverse event at 32%.

The most common major adverse events associated with the Seresto collar were neurological such as ataxia (loss of coordination), seizures, muscle tremors, and convulsions. The EPA did drill down on the numbers. In essence, the determination was that some of those events were possibly or probably due to the collars, but there was overall low confidence to rule definitively due to insufficient information such as a complete medical history and record.

The EPA concluded, “In a number of cases with moderate or severe clinical signs, removal of the collar often seemed to alleviate symptoms, and/or reapplication of the collar coincided with a reoccurrence of symptoms.”

In our opinion, that sentence is dismissive of the physical, emotional and financial burden placed by the collars on companion pets and their families.

Data Collection

Overall, data collection was the problem.

How was the data initially collected? Companion pet parents have many options to report pet incidents involving pesticides. They can contact their state’s pesticide regulatory agency, file a report with the manufacturer who is required by law to submit adverse events to the EPA, contact the EPA directly, or call the National Pesticide Information Center (NPIC) which provides summary reports to the EPA. The NPIC has a cooperative agreement between Oregon State University and the EPA. Veterinarians have a separate reporting portal with NPIC.

In July 2023, the EPA made the Incident Data System (IDS) available to the public, but had limited confidence in its accuracy. It is basically just raw, top-line data.

The data can be extracted either in Aggregate Incidents or Individual Incidents. The aggregate data divvies up the level of severity of the incident reported for an animal, human or something else like groundwater. However, the Aggregate does not provide the collector’s name of the data.

The database from Individual Incidents contains a field called “Overall Submission Description (may describe multiple incidents)”, which starts with the collector of the report. Bear in mind we could not identify some of the submitting collectors because they were listed by their acronyms.

The collector’s identity is followed by either a detailed description of the incident or minimal information.

However, the data do reveal how the separate entities report the data to the EPA.

In fact, we noticed that the majority of the reports submitted by the manufacturer prior to the 2023 mitigation measures gave minimal information.

As an example, incident report number 034220-00002, dated on January 1, 2018, states, “Elanco: Includes 1 H-B(-003) and 8 H-C. Symptoms include muscle tremor, dyskinesia, urticaria, etc. (JK)”.

They all read like that. Granted, more details may have been provided to the manufacturer or the EPA from the manufacturer, but they do not appear in this particular database.

If you are wondering, H-B describes a human major event, while H-C describes a human moderate event. Since the manufacturer’s data were submitted in bulk, we suppose that the submission may include animal adverse events that were not separated out in the Individual Incidents report. Empirically, human adverse events take precedence.

Other collectors also summarized the incidents occasionally, but many of them were more descriptive. We provide a few examples from the identifiable collecting office. Additionally, we only have provided incidents with dates preceding 2021.

028031-00001; July 1, 2015: U.S. DEPT. OF HEALTH & HUMAN SERVICES, FOOD AND DRUG ADMIN: Owner reports dog becomes lethargic whenever collar placed on him. The suspected product is Seresto Collar (Bayer Product)

029481-00001; November 1, 2016: U.S Consumer Product Safety Commission: received Dec 6, 2016, another dog death involving Seresto.

029952-00001; May 5, 2017: U.S. DEPT. OF HEALTH & HUMAN SERVICES: an Australian Shepard experienced stroke like symptoms after collar was place on dog.

029999-00001; June 2, 2017: NPIC: a dog became lethargic and uncoordinated each time the owner placed the collar around the dog’s neck.

030621-00001; November 12, 2017: NPIC: Nov. 2017, Seresto, another dead pet.

030799-00001; March 1, 2018: Incident Reporting Portal: March 2018, an 18 week old puppy became very lethargic and cried within hours of putting a new Seresto collar on. The owner took off the collar and she started acting normal within a few hours. The owner tried the collar on her again about a week later and she was lethargic within an hour.

030898-00001; April 4, 2018: Incident Reporting Portal: Apr 2018, another dog death allegedly from the use of the Seresto dog collar.

033005-00001; August 1, 2019: NPIC: An owner reported lethargy and diarrhea for her two dogs one day after application of Seresto Flea Collars (flumethrin, imidacloprid). She reported the collars were removed, both dogs were treated by a veterinarian, and both dogs recovered, but wished to report the incident.

034033-00001; May 1, 2019: NPIC: a Maltese lost use of his hind legs after Seresto collar was applied, soon after the dog died.

Mitigation Measures

Several mitigation measures have been imposed such as a 5-year registration that expires in mid-2028, education for veterinarians and companion pet parents, and a warning label that lists every condition that may be associated with the product.

Most importantly, Elanco, the manufacturer, has to use an enhanced adverse event reporting template, submit all reports to the EPA, and provide a summary. In regards to the detailed reports, mitigation measure #4 states:

“Elanco US Inc. must develop and implement additional efforts regarding case follow-up, referrals, and necropsies as medically indicated. Annually, Elanco US Inc. must review and update training materials, frequency of training, and technical solutions for collecting and providing data related to the pets involved in adverse event (AE) reports for all Elanco US Inc. staff responsible for taking in these data. Elanco US Inc. will, to the fullest extent possible, include the following information for each AE:

  1. Pre-existing medical conditions (e.g., hypothyroidism, diabetes), including previous history of reported condition.
    b. Medications concomitantly administered.
    c. Pet’s prior experience with the product.
    d. Pet health status.”

The enhanced reporting template’s narrative column states: “This cannot be left blank: Narrative of AE (open ended text). Chronological history that identifies relevant information: relevant medical history, reason for use of products, possible contributing factors, sites of response, severity of response, pertinent lab and diagnostic test values, treatment of AE, date of death (if applicable), necropsy results, pathology findings, comments on assessments from veterinarian, any other significant information.”

Our Thoughts

The EPA reporting was not originally conducive to successfully identify adverse events, but is currently rectifying the problem.

For example, “EPA’s reporting requirements allow registrants to submit domestic animal incidents as aggregate exposure counts and exposure severity without narrative details, the majority of the domestic animal data are merely counts of exposure severity types, by year.”

The agency’s difficulty here is apparent with this statement, “Specific confounding factors in case narratives included a lack of additional data around death reports (e.g., only claim was collar was placed on pet and then, at a later date, the pet died).”

The narratives submitted by governmental agencies and affiliates that we listed above were sketchy and come with limitations. For instance, NPIC does not collect information for enforcement nor does it provide EPA with any personal identifying information that could be used for follow-up.

While we think the EPA has corrected its course, gaps in procedure and collection information have not been fully addressed.

If NPIC cannot collect follow-up data, can any of the other agencies or affiliates do so going forward? Will all Seresto incident reports be directed to Elanco from the other agencies? Will there be audits taken of Elanco’s data collection to ensure the integrity of the data?

Only time will tell.

We would have preferred that the EPA required an independent 3rd party collect the data, and clarified the governmental agency collection methods going forward about Seresto collars.

Hettinger Articles; Investigative Midwest:

March 2, 2021: Popular flea collar linked to almost 1,700 pet deaths. The EPA has issued no warning.

March 18, 2021: House subcommittee seeks voluntary recall of Seresto flea and tick collars

June 2, 2021: Watchdog group finds toxic ‘forever chemicals’ in popular flea and tick collars

September 24, 2021: Seresto flea collar adverse incidents climb after company submits 11,000 more reports to EPA – Apparently, a miscommunication between Elanco and the EPA during the pandemic led to a delay in reporting.

November 4, 2021: SERESTO SHORT-FORM: What we’ve discovered so far about the popular collars linked to pet injuries and deaths – Includes documents that indicate the EPA rushed approval, and that the agency has been investigating Seresto collars since 2015.

March 24, 2022: EPA internally questioned its ability to properly regulate pet collars linked to tens of thousands of injury reports

October 13, 2022: EPA to ban flea and tick collars linked to brain damage in children – EPA to ban pet collars that contain tetrachlorvinphos (TCVP), but the spot-spot-on treatments are still on the market. In August 2023, we found TCVP collars still on the market. Seresto does not contain TCVP; its active ingredients are imidacloprid and flumethrin.

November 7, 2022: Popular flea collar Seresto has been linked to more than 100,000 reports of harm

July 14, 2023: EPA rules popular Seresto flea collar stays on the market, with more reporting requirements – Final article on Seresto collars

July 27, 2023: EPA posts databases of pesticide harm to people, pets and wildlife for first time in agency history


Dodds, W. Jean. Seresto Flea and Tick Collars and the EPA, Hemopet, 26 Mar. 2021,

Seresto Pet Collar Review, US EPA – U.S. Environmental Protection Agency, 13 July 2023,

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