Drug profile
The FDA adverse-event record for Levothyroxine
1,379 adverse-event reports submitted to the FDA Center for Veterinary Medicine reference Levothyroxine. See the species affected, top reactions, and outcomes below.
- 1,379
- adverse-event reports
- 11.5%
- death-coded share
- Dog
- most-reported species
- 218
- Vomiting - top reaction
Active Ingredients
Administration Routes
Species Affected
Most Affected Breeds
Most Reported Reactions
Outcome Breakdown
Levothyroxine Adverse Event Insights
1,379 reports name Levothyroxine; 159 recorded a death outcome (11.5% of reported events, not a population-level mortality rate). Active ingredient: Levothyroxine. Administration routes: Oral, Unknown, Ophthalmic.
By species: Dog (1,312 reports), Human (44 reports), Cat (16 reports). By breed: Retriever - Labrador (204), Retriever - Golden (129), Crossbred Canine/dog (76).
Leading clinical signs: Vomiting (218), Diarrhoea (158), Lethargy (see also Central nervous system depression in 'Neurological') (143), Elevated alanine aminotransferase (ALT) (103). Outcome, 1,362 coded reports: Ongoing leads at 35.8%.
Read these counts as reporting volume, not risk: per our methodology, a widely-prescribed drug will rack up more raw FDA reports in a given year than a rarely-used one at an identical true rate, so we recommend comparing within similar-exposure products rather than across the full 2025 catalog.
Source: FDA Center for Veterinary Medicine openFDA Animal & Veterinary Adverse Events (CVM AER) · 2025
Every figure on PlainBreed is rendered directly from FDA openFDA adverse event data, no number is typed in by an editor. This page draws directly on FDA openFDA data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.