Weight gain after Methimazole in cats

20 reports to the FDA describe weight gain in cats given Methimazole. That is 1.1% of all reports for this medicine, compared with 0.4% across reports for all cat medicines, so it is reported unusually often with this medicine.

20Reports

40%Marked serious

0.0%Recovered

15%Died or euthanised

33 daysTypical onset

How soon it started

Same day

0 0.0%

1–2 days

0 0.0%

3–7 days

0 0.0%

1–4 weeks

6 46%

Over a month

7 54%

How the animals did

Still unwell when reported

3 15%

Euthanised

3 15%

Not known

14 70%

Problems reported at the same time

Kidney problems

7 35%

Lethargy

5 25%

Elevated symmetrical dimethylarginine (sdma)

4 20%

4 20%

3 15%

3 15%

3 15%

Restlessness or agitation

3 15%

Age of the animals

Under 1 year

1–3 years

4–7 years

8–11 years

12+ years

About this medicine

Methimazole treats an overactive thyroid in cats.

Questions owners ask

Can Methimazole cause weight gain in cats?: 20 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 33 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 Velagliflozin (Senvelgo) 31 reports · 0.6% of its reports
Weight gain after Bexagliflozin (Bexacat) 256 reports · 6.3% of its reports
Weight gain after Insulin 20 reports · 0.5% of its reports

All reported side effects of Methimazole in cats · Medicines most reported with weight gain