Most-Reported Pet Medications

How We Counted Reports

The numbers in this guide come from the FDA openFDA Animal & Veterinary Adverse Events database, which covers reports from 2004 through the most recent quarterly update. Report counts represent unique adverse event submissions associated with each drug name, whether as a primary suspect drug or as a concomitant medication.

PlainBreed's drug directory covers 2,679 medications. The 15 listed here are the live top registry entries by report count, queried directly from the same database that backs the drug directory -- not a fixed, periodically-updated list. Because the FDA registers drugs per individual formulation rather than per active ingredient, the same drug can appear under several different names: 12 separately-named fluralaner (Bravecto) entries combine for 90,381 reports, split across formulations so that none individually cracks higher than #7 on its own. A generic like amoxicillin-clavulanate fragments even further: 31 separately-registered formulations sum to 9,571 reports combined, still outside the top 15 even fully aggregated.

One important caveat: report counts are not standardized by prescription volume. A drug used by 10 million animals will naturally accumulate more reports than a drug used by 50,000 animals, even if both carry identical per-use risk. Interpreting these numbers requires holding the usage context in mind.

Top 15 Most Reported Medications

The table below ranks the live top 15 drug registry entries by total adverse event report count across all species in the FDA openFDA database, queried at render time.

#	Drug Name	Top Species	Reports	Common Reactions
1	Milbemycin Oxime + Spinosad 2.3% death-coded	Dog, Unknown	149,624	Emesis, Vomiting
2	Ivermectin + Pyrantel As Pamoate Salt 2.0% death-coded	Dog, Unknown	92,684	Lack of efficacy (endoparasite) - heartworm, Lack of efficacy (endoparasite) - hookworm
3	Spinosad 2.5% death-coded	Dog, Cat	66,305	Emesis, Vomiting
4	Afoxolaner 3.2% death-coded	Dog, Unknown	53,894	Vomiting, Lethargy (see also Central nervous system depression in 'Neurological')
5	Pyrantel Pamoate;Sarolaner 1.7% death-coded	Dog, Unknown	52,116	Vomiting, Lack of efficacy (bacteria) - Borrelia
6	Moxidectin 3.5% death-coded	Dog, Unknown	46,778	Lack of efficacy (endoparasite) - heartworm, Vomiting
7	Fluralaner Chew Tablets 3.3% death-coded	Dog, Unknown	35,883	Vomiting, Lack of efficacy (ectoparasite) - flea
8	Milbemycin Oxime + Praziquantel 2.5% death-coded	Dog, Unknown	35,786	Lack of efficacy (endoparasite) - heartworm, Vomiting
9	Selamectin 3.3% death-coded	Cat, Dog	31,260	Lack of efficacy (ectoparasite) - flea, Application site alopecia
10	Oclacitinib Maleate 4.9% death-coded	Dog, Unknown	29,264	Lack of efficacy - NOS, Vomiting
11	Fluralaner 13.64% 12-Week Chew 2.5% death-coded	Dog, Unknown	28,569	Lack of efficacy (ectoparasite) - flea, Vomiting
12	Carprofen 15.1% death-coded	Dog, Unknown	23,400	Vomiting, Anorexia
13	Nitenpyram 3.2% death-coded	Dog, Cat	19,304	Lack of efficacy (ectoparasite) - flea, Panting
14	Imidacloprid + Moxidectin 4.0% death-coded	Dog, Cat	18,976	Lethargy (see also Central nervous system depression in 'Neurological'), Pruritus
15	Bedinvetmab 19.3% death-coded	Dog, Human	18,912	Death by euthanasia, Lethargy (see also Central nervous system depression in Neurological)

Source: FDA openFDA Animal & Veterinary Adverse Events API Live query, ranked by total_reports; updated as the underlying database refreshes

Compiled by PlainBreed.

The Isoxazoline Story

Isoxazoline-class antiparasitics are among the largest presences in this table, but the report count for the class is split across several separately-registered products and formulations rather than sitting under one name. Afoxolaner (NexGard) is the single largest isoxazoline entry at #4 with 53,894 reports. Fluralaner (Bravecto) fragments furthest: 12 differently-named registry entries (chew tablets, 12-week chews, spot-on solutions and more) combine for 90,381 reports -- more than any single entry in the table except the #1 combination product -- yet the largest individual Fluralaner entry only reaches #7. Sarolaner appears too, mostly bundled into combination products such as the pyrantel-sarolaner pairing at #5. Spinosad, the top entry in this table's own class (spinosyn, not isoxazoline), shares the same high-prescribing flea-prevention market that drives large report volumes across this whole drug category.

In 2018, the FDA issued a Drug Safety Communication specifically for isoxazolines, noting reports of neurological adverse reactions including muscle tremors, ataxia, and seizures in dogs and cats. The FDA required manufacturers to add updated labeling. This does not mean the drugs are prohibited, they remain approved, but it indicates that veterinarians and pet owners should be aware of this signal, particularly in animals with prior seizure history.

You can explore individual isoxazoline drug profiles on PlainBreed's drugs directory to see the full reaction breakdown and species distribution for each product.

NSAIDs and Pain Medications

Non-steroidal anti-inflammatory drugs (NSAIDs) are far less represented in the top 15 than the antiparasitic products above them. Carprofen is the only NSAID that reaches the top 15, at #12 with 23,400 reports. Meloxicam, the other commonly-prescribed NSAID, ranks #23 with 11,502 reports -- outside the top 15, well below the antiparasitic products that dominate this list.

What makes carprofen worth a second look is not its rank but its outcome profile: at 15.1% death-coded reports, it carries the highest death-coded share of any drug in the top 15 -- clearly higher than the antiparasitic products ranked above it (which cluster in the low single digits). Carprofen (sold as Rimadyl and generics) also has one of the longest adverse event records in the database due to its decades-long market presence and status as one of the most prescribed canine medications, which explains its high report count without on its own indicating it is disproportionately dangerous. The death-coded share is the more informative signal here than the raw report count.

NSAID adverse events in dogs are also linked to MDR1 genetic variants in herding breeds. If your dog is a Collie, Australian Shepherd, Shetland Sheepdog, or similar breed, discuss MDR1 testing with your veterinarian before starting NSAIDs or ivermectin-class drugs. Browse breed profiles on PlainBreed to see documented reactions for your dog's breed.

Antibiotics vs. Antiparasitic Drugs: a Fragmentation Contrast

Unlike the antiparasitic products that dominate the top 15, common antibiotics do not crack this list at all -- and the reason is itself informative. Metronidazole ranks #69 with 3,545 reports. Cephalexin ranks #81 with 2,780 reports. Amoxicillin-clavulanate is the starkest case: it is registered under 31 separately-spelled formulation names in this database (varying only in word order and abbreviation, e.g. "Amoxicillin Trihydrate; Clavulanate Potassium" vs. "Amoxicillin/Clavulanate"), and even summed across every one of them the family totals only 9,571 reports -- still short of the #15 cutoff. Widely-used generic antibiotics fragment across many inconsistently-named registry entries far more than the antiparasitic products above, which tend to sell under one or two dominant branded or combination names. Where these antibiotics do appear, their adverse event profiles are dominated by GI effects, vomiting and diarrhea, common across many antibiotic classes, with serious outcomes relatively rare compared to report volume.

Ivermectin is a notable exception in the antiparasitic category. The single-ingredient entry ranks #22 with 11,814 reports -- close to, but outside, the top 15 (the combination product "Ivermectin + Pyrantel" ranks much higher, at #2, because it is sold as a single named product rather than fragmenting). While ivermectin has a strong safety record in most animals, certain dog breeds, particularly herding breeds with the MDR1 (ABCB1) genetic mutation, can experience severe neurotoxicity at doses that are safe for other dogs. Reports for ivermectin disproportionately include neurological reactions: ataxia, dilated pupils, coma, and in some cases death.

Milbemycin oxime, another heartworm preventative, ranks #26 as a single-ingredient entry with 9,924 reports (its combination products with spinosad and praziquantel rank far higher, at #1 and #8 respectively) and carries a similar MDR1 caveat. The breed directory on PlainBreed includes breed-level data on these reports, allowing you to compare the ivermectin reaction profile specifically for herding breeds versus the general dog population.

Corticosteroids and Immunosuppressants

Corticosteroids do not reach the top 15 either, and for the same fragmentation reason as the antibiotics above. Prednisone ranks #30 (9,249 reports) and prednisolone ranks #106 (2,152 reports) as separate registry entries; the wider prednisone/prednisolone family spans 28 differently-named formulations (plain tablets, ophthalmic drops, combination products with trimeprazine or antibiotics) totaling 16,991 reports combined -- close to, but still short of, the #15 cutoff even fully aggregated. Their reported adverse events largely reflect expected pharmacological effects at therapeutic doses: increased thirst and urination, increased appetite, weight gain, and susceptibility to infections.

Long-term corticosteroid use is associated with more serious effects including adrenal suppression, diabetes mellitus, and opportunistic infections. These appear in the database at lower frequencies than the acute GI effects but represent the more clinically significant risks. Cyclosporine (Atopica), used for allergic dermatitis, ranks #25 with 10,043 reports and has a similar profile with additional concerns around papilloma formation and secondary infections in immunocompromised animals.

Cross-Referencing with Breed Data

PlainBreed allows you to approach adverse event data from two directions: by drug (which breeds appear in reports for a given medication?) and by breed (which drugs appear in reports for a given breed?). This cross-referencing is particularly valuable for high-report drugs where risk is not evenly distributed across the animal population.

For example, if you look at ivermectin reports filtered to Collie breeds, you will see a reaction profile dominated by neurological events, very different from the broader ivermectin population. This breed-specific lens is exactly the kind of insight the database can provide that a general drug insert cannot.

Start with the drugs directory to find a drug profile, then use the breeds directory to look up your pet's specific breed and see which drugs appear most in its reports.

What to Do Before Starting a New Medication

If your veterinarian recommends a medication that appears on this list, that alone is not a reason for concern, most pets tolerate these drugs without incident. But reviewing the drug's adverse event profile on PlainBreed before starting treatment can help you:

Identify the most commonly reported early warning signs to watch for
Understand whether your pet's breed is disproportionately represented in that drug's reports
Know which reactions are classified as serious versus minor
Have an informed conversation with your veterinarian about monitoring frequency
Know when to call the veterinarian or emergency clinic if a reaction occurs

You can also check the rankings section of PlainBreed for additional comparative data on breeds and species by report volume and outcome rates.

Frequently Asked Questions

Which pet medication has the most adverse event reports in the FDA database?

Antiparasitic drugs, particularly flea, tick, and heartworm preventatives, consistently top the adverse event list by total report count. Isoxazoline-class antiparasitics (including fluralaner and sarolaner) have accumulated tens of thousands of reports, primarily neurological in nature. High report counts partly reflect widespread prescribing, not just elevated risk. The FDA issued a warning about this drug class in 2018 and required updated labeling.

Does a high report count mean a medication is dangerous?

Not necessarily. Report counts are influenced by how widely a drug is prescribed, how long it has been on the market, and how actively the manufacturer solicits feedback. A drug taken by millions of animals will accumulate more reports than a niche drug, even if both have similar adverse event rates. The more meaningful metric is the proportion of reports that resulted in serious outcomes, hospitalization, disability, or death, compared to total reports.

Are topical flea treatments safer than oral medications for adverse events?

Both have adverse event records in the FDA database. Topical treatments can cause localized skin reactions and, in cats, serious systemic toxicity if a dog-formulated product is accidentally applied. Oral medications are associated more frequently with gastrointestinal reactions and, for some drug classes, neurological effects. The "safer" choice depends on your pet's species, weight, age, and health history, always a veterinary decision.

What species appear most in medication adverse event reports?

Dogs account for the largest share of reports by far, partly because dogs are more commonly medicated than other species and because many antiparasitic drugs are labeled specifically for dogs. Cats represent the second-largest group, with horses and livestock making up most of the remainder. Species-specific reports are especially valuable because drug metabolism differs significantly between dogs and cats, a dose safe for one can be toxic for the other.

How do I find adverse event data for a specific medication on PlainBreed?

Visit the Drugs directory at plainbreed.com/drugs/ and search or browse for your medication by name. Each drug profile lists total reports, outcome distribution, most common reactions, and the species most represented. You can cross-reference with the breed directory if you want to see whether specific breeds appear disproportionately in that drug's reports.

Should I avoid all medications that appear in the adverse event database?

No. Nearly every approved medication has some adverse event record, that is expected and does not indicate the drug is unsafe. The adverse event database exists to surface patterns that might otherwise go undetected. The question for any medication is whether the documented benefit outweighs the documented risk for your individual pet, in consultation with your veterinarian who knows your animal's complete health picture.

Sources

U.S. FDA openFDA, Animal & Veterinary Adverse Events API (api.fda.gov/animalandveterinary)
FDA Center for Veterinary Medicine, Drug Safety Communication: FDA Alerts Pet Owners and Veterinarians about Potential for Neurological Adverse Events with Isoxazoline Class of Drugs (September 2018)
FDA, Animal Drug Safety Communications (fda.gov/animal-veterinary/animal-drug-safety-information)
PlainBreed database, 2,679 drugs, 1,085,823 reports, 2010–2026 (openFDA source)

This content is for informational purposes only and does not constitute veterinary advice. Report counts are approximate and reflect the most recent quarterly openFDA update. Consult your veterinarian before starting, stopping, or changing any pet medication.