Most-Reported Pet Medication & Product Reactions

Updated 2026-07-20 · counted directly from the source data — every number is reproducible.

From the 500 most recent adverse-event reports for dogs and cats in the FDA's openFDA veterinary database. A report is an owner's or vet's account, not a confirmed causal link — the FDA publishes them for surveillance, and so do we.

Most-reported reactions — dogs (417 reports)

#	Reaction	Reports
1	Vomiting	58
2	Medication error NOS	46
3	Lack of efficacy (endoparasite) - heartworm	41
4	Lethargy (see also Central nervous system depression in Neurological)	35
5	Lack of efficacy (bacteria) - Borrelia	34
6	Diarrhoea	34
7	Lack of efficacy (endoparasite) - hookworm	32
8	Seizure NOS	28
9	Intentional misuse	26
10	Lack of efficacy (endoparasite) - roundworm NOS	24

Most-reported reactions — cats (83 reports)

#	Reaction	Reports
1	Medication error NOS	8
2	Ataxia	8
3	Not eating	6
4	Weight loss	6
5	Application site hair loss	5
6	Application site alopecia	5
7	Skin scab	5
8	Emesis (multiple)	4
9	Behavioural disorder NOS	4
10	Lack of efficacy (ectoparasite) - flea	4

Full dataset & downloads