Weight gain after Levothyroxine in dogs

51 reports to the FDA describe weight gain in dogs given Levothyroxine. That is 1.7% 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.

51Reports

43%Marked serious

14%Recovered

5.9%Died or euthanised

96 daysTypical onset

How soon it started

Same day

4 13%

1–2 days

1 3.1%

3–7 days

0 0.0%

1–4 weeks

1 3.1%

Over a month

26 81%

How the animals did

Recovered

6 12%

Recovered with lasting effects

1 2.0%

Still unwell when reported

19 37%

Euthanised

3 5.9%

Not known

22 43%

Problems reported at the same time

Didn't work as expected

26 51%

12 24%

10 20%

7 14%

7 14%

6 12%

Skin rash or irritation

6 12%

Kidney problems

6 12%

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 gain in dogs?: 51 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 96 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 Trilostane (Vetoryl) 390 reports · 3.3% of its reports
Weight gain after Insulin 29 reports · 0.4% of its reports

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