Weight loss after Ivermectin (Heartgard) in dogs

The FDA has received 200 reports of weight loss in dogs after Ivermectin. That is 1.7% of all reports for this medicine, compared with 1.7% across reports for all dog medicines.

200Reports

55%Marked serious

16%Recovered

23%Died or euthanised

84 daysTypical onset

How soon it started

Same day

11 10%

1–2 days

7 6.5%

3–7 days

6 5.6%

1–4 weeks

14 13%

Over a month

70 65%

How the animals did

Recovered

21 11%

Recovered with lasting effects

10 5.0%

Still unwell when reported

61 31%

Died

12 6.0%

Euthanised

33 17%

Not known

63 32%

Problems reported at the same time

81 41%

70 35%

68 34%

49 25%

46 23%

43 22%

Didn't prevent heartworm

38 19%

Kidney problems

34 17%

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 loss in dogs?: 200 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 84 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 loss with similar medicines

Weight loss after Ivermectin + Pyrantel (Heartgard Plus) 889 reports · 0.6% of its reports
Weight loss after Milbemycin Oxime + Spinosad (Trifexis) 1,989 reports · 1.5% of its reports
Weight loss after Moxidectin (ProHeart 6) 858 reports · 1.7% of its reports
Weight loss after Milbemycin Oxime + Praziquantel (Interceptor Plus) 515 reports · 1.6% of its reports
Weight loss after Milbemycin Oxime (Interceptor) 348 reports · 1.2% of its reports
Weight loss after Selamectin (Revolution) 230 reports · 0.8% of its reports
Weight loss after Ivermectin + Praziquantel + Pyrantel (Iverhart Max) 42 reports · 0.5% of its reports
Weight loss after Moxidectin + Pyrantel + Sarolaner (Simparica Trio) 29 reports · 2.5% of its reports

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