Guide
Flea and Tick Medication Safety: What the FDA Data Shows
According to FDA CVM openFDA filings as of July 2026 extract, flea and tick products are among the most commonly reported drug categories in the FDA's animal adverse event database. Here's what the data reveals and how to use it when making decisions about parasite prevention.
If your pet is showing a reaction right now
Remove or wash off any topical product immediately with mild soap and water, then contact your veterinarian or an emergency veterinary clinic right away, especially for tremors, seizures, uncoordinated movement, excessive drooling, vomiting, or lethargy. Bring the product packaging (name, active ingredient, lot number). The ASPCA Animal Poison Control Center is also available 24/7.
Read this first
Among the four FDA-alerted isoxazoline products, Bravecto (fluralaner) has the highest death-coded report share at 3.3%, and Credelio (lotilaner) the lowest at 2.6% -- a real difference, but all four sit within a few tenths of a point of each other, none stands out as categorically safer.
- 3.2%
- NexGard -- 53,894 reports
- 3.3%
- Bravecto -- 35,883 reports
- 3.1%
- Simparica -- 17,358 reports
- 2.6%
- Credelio -- 12,153 reports
Permethrin-containing dog products remain a leading cause of cat poisoning -- never a species-safety question the report-volume numbers alone can answer; see 'Permethrin Toxicity in Cats' below.
Isoxazoline products by death-coded report share
The four FDA-alerted (2018) isoxazoline flea/tick products, FDA CVM Animal Adverse Event database
The Isoxazoline Class: What the FDA Alert Means
In September 2018, the FDA issued a safety alert for the entire isoxazoline class of flea and tick medications, oral products that work by making the animal's blood toxic to parasites. The alert covered four products: NexGard (afoxolaner), Bravecto (fluralaner), Simparica (sarolaner), and Credelio (lotilaner).
The FDA's review identified adverse event reports describing neurological reactions including muscle tremors, ataxia (loss of coordination), and seizures in dogs and cats following isoxazoline administration. Some of these events occurred in animals with no prior history of neurological conditions. As a result, the FDA required all isoxazoline product labels to include a warning about the potential for these effects.
Context matters: isoxazolines are among the most widely prescribed flea and tick products globally. Hundreds of millions of doses have been administered since their introduction. The number of adverse event reports, while significant enough to trigger an FDA action, represents a very small fraction of total doses. The products remain on the market because the FDA concluded that the benefits outweigh the risks for most animals, provided veterinarians and pet owners are informed about the potential neurological effects.
Explore isoxazoline-related reports in PlainBreed's drug profiles to see total report counts, reaction types, and breed-level breakdown.
Permethrin Toxicity in Cats
Permethrin is a synthetic pyrethroid insecticide used in many spot-on flea and tick products designed for dogs. It is highly effective against parasites in dogs but extremely toxic to cats. The difference is metabolic: cats lack the hepatic enzyme (glucuronyl transferase) required to break down permethrin safely. What is a therapeutic dose for a dog can be a lethal dose for a cat.
The FDA adverse event database contains a significant number of cat deaths and serious reactions linked to permethrin exposure. The most common scenario is a pet owner applying a dog-labeled spot-on product to a cat, not realizing the ingredients differ between species-specific formulations. Secondary exposure, a cat grooming or sleeping next to a recently treated dog, has also caused toxicity.
Symptoms of permethrin poisoning in cats include: muscle tremors (often beginning in the ears and paws), seizures, hypersalivation, vomiting, ataxia, and hyperthermia. Onset is typically within hours of exposure. This is a veterinary emergency, untreated permethrin toxicity in cats has a high mortality rate. With aggressive treatment (IV fluids, muscle relaxants, temperature management), survival rates are good if treatment begins early.
The rule is absolute: never use a dog flea product on a cat. Check the label species designation before every application. In multi-pet households, separate treated dogs from cats until the product has dried completely (topicals) or as directed on the label.
Comparing Flea and Tick Product Categories
Different flea and tick product types have different safety profiles in the FDA database. Here is how the major categories compare:
| Category | Examples | Key Concerns in FDA Data |
|---|---|---|
| Isoxazolines (oral) | NexGard, Bravecto, Simparica, Credelio | Neurological events (tremors, seizures, ataxia) - FDA alert issued 2018 |
| Topical spot-on (dogs) | Frontline, Advantix, various permethrin products | Skin reactions (redness, hair loss at site); permethrin cross-species toxicity to cats |
| Topical spot-on (cats) | Frontline, Advantage, Revolution | Skin reactions; some reports of neurological effects with high-concentration fipronil |
| Flea collars | Seresto, various | Skin irritation, hair loss at collar site; EPA reviewed Seresto reports 2021 |
| Oral (non-isoxazoline) | Capstar (nitenpyram), Comfortis (spinosad) | GI effects (vomiting, diarrhea) most common; generally considered well-tolerated |
No flea and tick product category has zero adverse events in the FDA database. The question is not whether a product is "safe" in absolute terms, but whether its risk profile is acceptable for your specific animal given the alternative, which is exposure to fleas, ticks, and the diseases they carry (Lyme disease, anaplasmosis, ehrlichiosis, Rocky Mountain spotted fever, flea allergy dermatitis, tapeworms). For most animals, the risk of parasite-borne disease far exceeds the risk of adverse drug reactions.
Using PlainBreed Data for Flea and Tick Decisions
PlainBreed's database lets you investigate flea and tick medication safety at a more granular level than the FDA's summary alerts. Here is how to use it:
- Search for your pet's breed profile and review the top drugs and reactions associated with that breed.
- Look at specific flea and tick products in the drug directory to see total reports, species breakdown, and most common reactions for each product.
- Compare the serious outcome rate (deaths + life-threatening events as a percentage of total reports) between products you are considering. A product with 10,000 total reports and a 2% death rate has a different risk profile than one with 500 reports and a 15% death rate.
- Check the reactions directory for specific symptoms you want to monitor, tremors, seizures, skin reactions, and see which products are most associated with each.
- If your dog is in a herding breed (Collie, Australian Shepherd, Shetland Sheepdog), check whether the product you are considering has elevated reports for that breed, some herding breeds have genetic sensitivities that affect drug metabolism.
Frequently Asked Questions
Are isoxazoline flea and tick products safe for my dog?
For the vast majority of dogs, isoxazolines (Bravecto, NexGard, Simparica, Credelio) are effective and well-tolerated. The FDA's 2018 alert was based on adverse event reports showing neurological side effects, muscle tremors, ataxia, and seizures, in a small number of dogs. The overall incidence rate is very low relative to the millions of doses administered annually. However, the FDA considers the signal significant enough to warrant labeling changes. Dogs with a history of seizures are at elevated risk. Discuss your dog's specific medical history with your veterinarian before starting any flea and tick medication.
Can I use a dog flea product on my cat?
Never use a dog flea product on a cat without explicit veterinary guidance. Products containing permethrin, a common ingredient in many dog flea and tick treatments, are toxic to cats and can cause fatal poisoning. Cats lack a liver enzyme (glucuronyl transferase) needed to metabolize permethrin. Even indirect exposure (a cat grooming a recently treated dog) can be dangerous. The FDA adverse event database contains numerous cat deaths linked to permethrin exposure from dog products. Always use species-specific products.
What should I do if my pet has a reaction to a flea and tick product?
Remove or wash off topical products immediately with mild soap and water. Contact your veterinarian or an emergency veterinary clinic, especially if you observe neurological signs (tremors, seizures, uncoordinated movement), excessive drooling, vomiting, or lethargy. Bring the product packaging with you, the veterinarian will need the product name, active ingredient, and lot number. After your pet has been treated, file an adverse event report with the FDA through safetyreporting.hhs.gov or 1-888-FDA-VETS.
Are natural or essential oil-based flea products safer?
Not necessarily. "Natural" does not mean non-toxic. Some essential oils used in flea products (tea tree oil, pennyroyal, certain citrus oils) can be toxic to pets, particularly cats. The FDA and EPA have issued warnings about adverse reactions to essential oil-based pest products. Additionally, natural products are generally less effective than FDA-approved medications and may not provide adequate flea and tick protection, which carries its own risks (Lyme disease, anaplasmosis, flea allergy dermatitis). Evaluate all products, natural or pharmaceutical, based on evidence, not marketing claims.
How does the FDA decide to add safety warnings to flea and tick products?
The FDA monitors adverse event reports continuously through its pharmacovigilance system. When a pattern of concerning events emerges, such as the neurological reports associated with isoxazolines, the CVM investigates the signal: reviewing the reports in detail, consulting clinical literature, evaluating the biological plausibility, and assessing whether the events exceed the expected background rate. If the evidence supports a safety concern, the FDA may require label changes (additional warnings, contraindications), issue Dear Veterinarian letters, publish safety alerts, or in severe cases, require additional studies or product modifications.
Sources
- FDA Center for Veterinary Medicine - "FDA Alert: Potential Neurological Adverse Events in Dogs and Cats Treated with Isoxazoline Flea and Tick Products" (September 2018)
- U.S. FDA openFDA, Animal & Veterinary Adverse Events API (api.fda.gov/animalandveterinary)
- EPA - "EPA Evaluation of Pet Spot-on Products: Analysis of Reports and Incident Data" (2010)
- ASPCA Animal Poison Control Center, Permethrin Toxicity in Cats
- Journal of Veterinary Internal Medicine, Isoxazoline safety reviews and post-market surveillance studies
- PlainBreed database, openFDA source, 1M+ reports
This content is for informational purposes only and does not constitute veterinary advice. Consult your veterinarian about flea and tick prevention options for your specific pet.
What this means for you
No flea/tick product category has zero adverse events -- the comparison that matters is between the product you're considering and the parasite-borne diseases it prevents.
- Among the four isoxazoline products, death-coded share ranges 2.6%-3.3% -- a narrow spread, so the FDA's 2018 alert applies to the whole class, not one standout product. Browse isoxazoline drug profiles
- Never use a dog-labeled permethrin product on a cat -- cats lack the liver enzyme to metabolize it, and even secondary exposure from grooming a treated dog can be fatal. Permethrin toxicity in cats
- If your dog is a herding breed with the MDR1 mutation, check that breed's own drug-reaction profile before starting any new flea/tick product. Browse breeds
Every figure is a live count from the FDA CVM openFDA extract, voluntary and unverified reports, not proof of cause and effect.
The isoxazoline death-coded comparison chart and its underlying report counts are queried live from FDA openFDA adverse event data at render time. Other figures in this guide (FDA alert dates, mechanism descriptions) are drawn from FDA and EPA published safety communications, cited in Sources below. This page's data-linked figures draw directly on FDA openFDA data. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.