Weight loss after Levothyroxine in dogs

206 reports to the FDA describe weight loss in dogs given Levothyroxine. That is 6.8% of all reports for this medicine, compared with 1.7% across reports for all dog medicines, so it is reported unusually often with this medicine.

206Reports

69%Marked serious

19%Recovered

19%Died or euthanised

50 daysTypical onset

How soon it started

Same day

15 12%

1–2 days

3 2.3%

3–7 days

10 7.7%

1–4 weeks

27 21%

Over a month

75 58%

How the animals did

Recovered

31 15%

Recovered with lasting effects

8 3.9%

Still unwell when reported

53 26%

Died

10 4.9%

Euthanised

29 14%

Not known

75 36%

Problems reported at the same time

85 41%

64 31%

58 28%

47 23%

43 21%

39 19%

37 18%

27 13%

Age of the animals

Under 1 year

1–3 years

4–7 years

8–11 years

12+ years

About this medicine

Levothyroxine treats an underactive thyroid.

Questions owners ask

Can Levothyroxine cause weight loss in dogs?: 206 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 50 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 Trilostane (Vetoryl) 1,496 reports · 13% of its reports
Weight loss after Insulin 304 reports · 4.1% of its reports
Weight loss after Phenylpropanolamine (Proin) 123 reports · 3.0% of its reports

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