Methadone
272 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 | 272 |
| Reports involving death | 65 |
| Case-fatality rate (reported events) | 2390.0% |
| Distinct species in reports | 5 |
| 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.
Methadone Adverse Event Insights
The FDA Center for Veterinary Medicine database currently holds 272 adverse event reports referencing Methadone, including 65 reports in which the animal died — a 2390.0% case-fatality figure among reported events only, not a population-level mortality rate. Active ingredient on file: Methadone. Reported administration routes include Unknown, Intravenous, Intramuscular, Parenteral. 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 Methadone reports are Dog (195 reports), Cat (73 reports), Human (2 reports), with Dog accounting for the largest share. Within those species, Domestic Shorthair (37), Retriever - Labrador (26), Dog (unknown) (13) 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 Methadone are Lethargy (see also Central nervous system depression in Neurological) (40), Death by euthanasia (36), Not eating (36), Diarrhoea (35). Of the 274 reports with a coded outcome, Recovered/Normal is the leading category at 34.7%. 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 Methadone.
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.