Lethargy after Ivermectin (Heartgard) in horses

92 reports to the FDA describe lethargy in horses given Ivermectin. That is 13% of all reports for this medicine, compared with 7.9% across reports for all horse medicines, so it is reported unusually often with this medicine.

92Reports

1.1%Marked serious

4.3%Recovered

17%Died or euthanised

–Typical onset

How the animals did

Recovered

4 4.3%

Still unwell when reported

1 1.1%

Died

15 16%

Euthanised

1 1.1%

Not known

71 77%

Problems reported at the same time

22 24%

22 24%

20 22%

17 18%

15 16%

14 15%

9 9.8%

8 8.7%

Age of the animals

Under 1 year

1–3 years

4–7 years

8–11 years

12+ years

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.

Questions owners ask

Can Ivermectin cause lethargy in horses?: 92 reports link the two, but a report alone does not prove the medicine was the cause: other illnesses, other medicines or coincidence can be involved. Your vet can judge it for your animal.
What should I do?: Don't give another dose until you've spoken to your vet, and keep the packaging so you can tell them the product and dose. Your vet can also report it to the FDA (or you can, through the manufacturer or FDA form 1932a).

Lethargy with similar medicines

Lethargy after Ivermectin + Praziquantel 187 reports · 7.1% of its reports
Lethargy after Moxidectin (ProHeart 6) 254 reports · 19% of its reports
Lethargy after Moxidectin + Praziquantel 55 reports · 15% of its reports

All reported side effects of Ivermectin in horses · Medicines most reported with lethargy