Levothyroxine — 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 2026-07-22. Counts are report-level: one report may list multiple reactions and multiple animals, so figures are not additive and do not imply causation. Levothyroxine is a active ingredient.
Total reports
Levothyroxine: 1497
Reports by species (top entries)
- Dog 1419
- Human 48
- Cat 17
- Horse 6
Top reported reactions (VEDDRA terms, top entries)
- Vomiting 232
- Diarrhoea 168
- Lethargy (see also Central nervous system depression in 'Neurological') 145
- Anorexia 112
- Death by euthanasia 109
- Elevated alanine aminotransferase (ALT) 109
- Lack of efficacy - NOS 108
- Other abnormal test result NOS 104
- Weight loss 101
- Polydipsia 88
Source JSON: pdf-raw/ade/ade_active_ingredients_2026-07-22_b10.json (openFDA animalandveterinary/event.json, pulled 2026-07-22).