Methimazole — FDA Animal & Veterinary Adverse Event (ADE) Reports
Source: openFDA animalandveterinary/event.json, the FDA Center for Veterinary Medicine (CVM) adverse event report database. Data pulled 2026-07-21. Counts are report-level: one report may list multiple reactions and multiple animals, so figures are not additive and do not imply causation. Methimazole is a antithyroid (feline hyperthyroidism).
Total reports
Methimazole: 1225
Reports by species (top entries)
- Cat 1194
- 5
- Dog 3
Top reported reactions (VEDDRA terms, top entries)
- Vomiting 205
- Weight loss 144
- Anorexia 114
- Lack of efficacy - NOS 110
- Lethargy (see also Central nervous system depression in Neurological) 105
- Not eating 103
- Death by euthanasia 89
- Lethargy (see also Central nervous system depression in 'Neurological') 86
- Diarrhoea 78
- Decreased appetite 72
"Lack of efficacy" terms denote product-performance reports, not adverse reactions.
Source JSON: pdf-raw/ade/ade_active_ingredients_2026-07-21.json (openFDA animalandveterinary/event.json, pulled 2026-07-21).