Diphenhydramine
2,668 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 | 2,668 |
| Reports involving death | 211 |
| Case-fatality rate (reported events) | 790.0% |
| Distinct species in reports | 6 |
| 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.
Diphenhydramine Adverse Event Insights
The FDA Center for Veterinary Medicine database currently holds 2,668 adverse event reports referencing Diphenhydramine, including 211 reports in which the animal died — a 790.0% case-fatality figure among reported events only, not a population-level mortality rate. Active ingredient on file: Diphenhydramine. Reported administration routes include Unknown, Oral, 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 Diphenhydramine reports are Dog (2,475 reports), Cat (176 reports), Human (14 reports), with Dog accounting for the largest share. Within those species, Retriever - Labrador (245), Crossbred Canine/dog (129), Chihuahua (113) 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 Diphenhydramine are Vomiting (582), Emesis (339), Lethargy (see also Central nervous system depression in 'Neurological') (332), Diarrhoea (322). Of the 2,666 reports with a coded outcome, Recovered/Normal is the leading category at 37.6%. 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 Diphenhydramine.
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.