Weight gain after Ivermectin (Heartgard) in dogs

The FDA has received 140 reports of weight gain in dogs after Ivermectin. That is 1.2% of all reports for this medicine, compared with 0.6% across reports for all dog medicines, so it is reported unusually often with this medicine.

140Reports

27%Marked serious

25%Recovered

2.9%Died or euthanised

157 daysTypical onset

How soon it started

Same day

6 9.8%

1–2 days

0 0.0%

3–7 days

0 0.0%

1–4 weeks

8 13%

Over a month

47 77%

How the animals did

Recovered

20 14%

Recovered with lasting effects

15 11%

Still unwell when reported

22 16%

Died

2 1.4%

Euthanised

2 1.4%

Not known

79 56%

Problems reported at the same time

Didn't prevent heartworm

69 49%

Vomiting

35 25%

Weight loss

19 14%

Didn't work as expected

16 11%

15 11%

13 9.3%

13 9.3%

13 9.3%

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 weight gain in dogs?: 140 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 157 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).

Weight gain with similar medicines

Weight gain after Ivermectin + Pyrantel (Heartgard Plus) 596 reports · 0.4% of its reports
Weight gain after Milbemycin Oxime + Spinosad (Trifexis) 2,619 reports · 2.0% of its reports
Weight gain after Moxidectin (ProHeart 6) 93 reports · 0.2% of its reports
Weight gain after Milbemycin Oxime + Praziquantel (Interceptor Plus) 575 reports · 1.8% of its reports
Weight gain after Milbemycin Oxime (Interceptor) 145 reports · 0.5% of its reports
Weight gain after Selamectin (Revolution) 47 reports · 0.2% of its reports
Weight gain after Ivermectin + Praziquantel + Pyrantel (Iverhart Max) 23 reports · 0.3% of its reports
Weight gain after Moxidectin + Pyrantel + Sarolaner (Simparica Trio) 23 reports · 2.0% of its reports

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