Methimazole
1,035 adverse event reports submitted to the FDA
Active Ingredients
Administration Routes
Species Affected
Most Affected Breeds
Most Reported Reactions
Outcome Breakdown
Data Summary
| Metric | Value |
|---|---|
| Total adverse event reports | 1,035 |
| Reports involving death | 146 |
| Case-fatality rate (reported events) | 1410.0% |
| Distinct species in reports | 3 |
| Distinct breeds in reports | 20 |
| Distinct reactions reported | 20 |
| Active ingredients on file | 1 |
Source: FDA Center for Veterinary Medicine — Adverse Event Reporting (CVM AER). Counts reflect voluntary reports only.
Methimazole Adverse Event Insights
The FDA Center for Veterinary Medicine database currently holds 1,035 adverse event reports referencing Methimazole, including 146 reports in which the animal died — a 1410.0% case-fatality figure among reported events only, not a population-level mortality rate. Active ingredient on file: Methimazole. Reported administration routes include Unknown, Oral, Topical, Transdermal. These numbers reflect voluntary submissions from pet owners, veterinarians, and manufacturers and therefore under-represent mild events and over-represent severe ones — a pattern the FDA has documented repeatedly for pharmacovigilance datasets.
The species most frequently named in Methimazole reports are Cat (1,017 reports), Unknown (16 reports), Dog (2 reports), with Cat accounting for the largest share. Within those species, Domestic Shorthair (685), Domestic Longhair (96), Domestic Mediumhair (55) appear most often — though breed popularity and ownership density shape these counts as much as any drug-specific sensitivity. This distribution matters because the same active ingredient can behave very differently across body sizes, ages, and species physiology.
The most commonly reported clinical signs associated with Methimazole are Vomiting (173), Weight loss (106), Anorexia (97), Lack of efficacy - NOS (93). Of the 994 reports with a coded outcome, Ongoing is the leading category at 38.4%. Because FDA adverse event data describes correlation rather than causation, these figures are best used to frame informed questions with a veterinarian and to compare reporting patterns across related products — not as a standalone safety verdict on Methimazole.
Source: FDA Center for Veterinary Medicine — Adverse Event Reports FDA Center for Veterinary Medicine — Adverse Event Reports Data reflects voluntary submissions and may not represent actual incidence rates
Read our methodology — how this data is sourced, computed, and verified.