Lethargy after Ivermectin (Heartgard) in dogs

1,488 reports to the FDA describe lethargy in dogs given Ivermectin. That is 12% of all reports for this medicine, compared with 11% across reports for all dog medicines.

1,488Reports

30%Marked serious

38%Recovered

10%Died or euthanised

20 daysTypical onset

How soon it started

Same day

184 22%

1–2 days

96 11%

3–7 days

61 7.2%

1–4 weeks

128 15%

Over a month

379 45%

How the animals did

Recovered

462 31%

Recovered with lasting effects

99 6.7%

Still unwell when reported

213 14%

Died

93 6.3%

Euthanised

60 4.0%

Not known

561 38%

Problems reported at the same time

545 37%

422 28%

283 19%

221 15%

183 12%

149 10%

Eye or vision problems

145 9.7%

Drooling

130 8.7%

Age of the animals

Under 1 year

329

1–3 years

415

4–7 years

317

8–11 years

250

12+ years

114

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 dogs?: 1,488 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.
How soon after a dose was it reported?: In half of the reports with dates, it started within 20 days of the first dose.
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 + Pyrantel (Heartgard Plus) 7,391 reports · 5.0% of its reports
Lethargy after Milbemycin Oxime + Spinosad (Trifexis) 19,835 reports · 15% of its reports
Lethargy after Moxidectin (ProHeart 6) 6,640 reports · 13% of its reports
Lethargy after Milbemycin Oxime + Praziquantel (Interceptor Plus) 2,407 reports · 7.6% of its reports
Lethargy after Milbemycin Oxime (Interceptor) 2,528 reports · 8.5% of its reports
Lethargy after Selamectin (Revolution) 2,964 reports · 10% of its reports
Lethargy after Ivermectin + Praziquantel + Pyrantel (Iverhart Max) 969 reports · 11% of its reports
Lethargy after Moxidectin + Pyrantel + Sarolaner (Simparica Trio) 135 reports · 12% of its reports
Lethargy after Ivermectin + Praziquantel 35 reports · 17% of its reports
Lethargy after Moxidectin + Praziquantel 21 reports · 28% of its reports

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