Ivermectin (Heartgard) side effects in cats
965 reports sent to the FDA between 1995 and 2026 involve Ivermectin in cats. The most reported problems were vomiting, wobbliness (ataxia), lethargy. 20% were marked serious, and where it was recorded, signs eased after stopping the medicine in 0% of cases.
About this medicine
Ivermectin prevents heartworm disease (monthly).
Products with this ingredient include Heartgard. The FDA hides brand names in its public data, so these reports cover every product with the same active ingredients.
Some herding breeds (for example Collies) carry the MDR1 gene variant and can be more sensitive to this drug class at high doses.
Most reported side effects
Share = percentage of this medicine's reports that mention the problem. One report can list several problems.
Reports that it didn't work
Some reports are about the medicine not working (for example a cat still getting fleas or heartworm), not about a side effect.
How soon problems started
Time from the first dose to the first sign, where both dates were reported (246 reports).
How the animals did
Breeds named most often
Popular breeds appear more often because there are more of them.
- Domestic 404 reports
- Domestic Shorthair 194 reports
- Siamese 28 reports
- Domestic Mediumhair 25 reports
- Persian 19 reports
- Domestic Longhair 16 reports
- Maine Coon 14 reports
- European 9 reports
- Ragdoll 7 reports
- Bengal 5 reports