Ivermectin (Heartgard) side effects in horses
689 reports sent to the FDA between 1995 and 2026 involve Ivermectin in horses. The most reported problems were abdominal pain, swelling, lethargy. 9.6% were marked serious, and where it was recorded, signs eased after stopping the medicine in 44% 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 horse 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 (90 reports).
How the animals did
Breeds named most often
Popular breeds appear more often because there are more of them.
- Quarter Horse 171 reports
- Horse 164 reports
- Thoroughbred 55 reports
- Miniature 34 reports
- Paint 31 reports
- Horse (other) 27 reports
- Arab 25 reports
- Standardbred 16 reports
- Appaloosa 12 reports
- Tennessee Walking Horse 12 reports