The Growing Concerns Surrounding Flea and Tick Products for Dogs

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For over ten years, I have written on this blog about using non-toxic flea and tick products. And the research is growing exponentially concerning the effects the use of Isoxazoline products on our pets. In 2018, the US Food and Drug Administration (FDA) issued an alert to inform companion pet parents about certain flea and tick products that contain drugs from the isoxazoline class. While the FDA still considers these products safe and effective for treating or preventing flea and tick infestations, they do warn about potential neurologic adverse reactions in some dogs and cats. Let’s explore the latest information and research on these products and provide insights for pet owners to consider.

The Isoxazoline Products and Associated Risks

The flea and tick products in question include Bravecto (fluralaner) tablets and topical solution, Credelio (lotilaner) tablets, Nexgard (afoxolaner) tablets, and Simparica (sarolaner) tablets. There are also additional products that offer protection against heartworm and worms, such as Bravecto Plus (fluralaner and moxidectin) topical solution, Simparica Trio (sarolaner, moxidectin, and pyrantel) tablets, and Revolution Plus (selamectin and sarolaner) topical solution for cats.

Accumulative Effects of Isoxazoline Drugs

Contrary to common belief, adverse reactions to these products may not occur immediately after administration. Recent research has shed light on the cumulative effect of isoxazoline drugs in the body. A study conducted in Argentina in 2023 found that fluralaner, one of the active ingredients, accumulates in fat tissues. The study suggests that if not properly controlled, this accumulation could lead to high local concentrations in different organs and membranes, posing a potential danger to vertebrate organisms.

While the study was not specifically conducted on companion dogs and cats, survey data from the European Medicines Agency (EMA) indicates the possibility of accumulation in the body. Project Jake, an independent survey conducted in North America, compared its data with the FDA and EMA reports. According to Project Jake’s findings, the most serious adverse events occurred within 0-24 hours after the first dose and after subsequent doses, indicating a cumulative effect.

Age and Cumulative Effects

The data from the EMA shows a correlation between age and adverse events in companion dogs. Dogs over the age of five experienced a higher incidence of adverse events, including seizures and death, potentially suggesting a cumulative effect of these drugs in the body over time. Further research is needed to explore this association.

Expert Recommendations and Precautions

Dr. Dodds, a renowned veterinarian, does not recommend using drugs from the isoxazoline class for flea and tick prevention or treatment. Instead, she suggests exploring other, preferably all-natural options.

If you choose to use these flea and tick products, it is advisable to separate their administration from monthly heartworm preventatives by at least 15 days. Additionally, consider using them only during months when there is a heavy burden of fleas, ticks, or worms in your area or when your household is more susceptible. For example, if tick infestations are prevalent in May or June but not during the rest of the warm weather months, limit the use of these products to those specific times.

Dr. Dodds still recommends monthly–or every 45 days if you can responsibly manage the schedule–heartworm preventatives if the temperature has been consistently above 57 degrees Fahrenheit for approximately two weeks and mosquitoes are prevalent. In Northern states, this typically occurs between May and November, while in Southern states, it may be necessary year-round. See the list here.

The use of flea and tick products containing isoxazoline drugs continues to be a topic of concern. While the FDA considers them safe and effective, potential neurologic adverse reactions have been associated with their use. Ongoing research suggests a cumulative effect of these drugs in the body, highlighting the need for further investigation. As a companion pet parent, it is essential to carefully consider the risks and make informed decisions regarding flea and tick prevention and treatment for your beloved pets.

My Personal Opinion and Experience on Using Natural Flea and Tick Products for over 10 Years

Plant powered peppermint scented flea and tick collar for dogs and cats

I’ve used natural products on my dogs for at least 10 years. And except for a glitch last fall, since the area I was hunting had no ticks and I was traveling and I backed off the garlic (I kept forgetting to pick up some when I made it to a town with a store) and natural spray for approximately two weeks, and then traveled to another state and was covered in ticks within 5 minutes of getting out of the truck. It took another few weeks for the garlic to build back up, but the natural sprays worked. Will natural products keep every tick off your dog? Maybe not. But I believe with the combination of fresh garlic and the natural sprays, you will certainly keep most off. Be diligent with the combination and grooming your dog every night. I love TripleSure Flea and Tick Spray and Wondercide products. Wondercide has collars now, and I love them for the dog that doesn’t appreciate sprays. Tip: Spray it on your hands first and then run your hands over the dog. Most dogs don’t like to be sprayed. The smell is pleasant (cedar, lemongrass, peppermint) and knowing I am not harming my dogs with chemicals that build up in their systems and cause health problems later in their life (and mine), I can sleep better. They are not chemical-laden dogs, their immune systems are not damaged by pesticides, insecticides, and processed garbage foods, and if they get Lyme or another ailment, they are healthier to fight off illness. I urge you–beg you–to stop using the chemicals on your dogs.


Wells, C., Collins, C.M.T. A rapid evidence assessment of the potential risk to the environment presented by active ingredients in the UK’s most commonly sold companion animal parasiticides. Environ Sci Pollut Res 29, 45070–45088 (2022).

Diepens, N., Belgers, D., Buijse, L., & Roessink, I. (2023). Pet dogs transfer veterinary medicines to the environment. Science of The Total Environment858, 159550.