Didn't work as expected after Methimazole in cats

203 reports to the FDA describe didn't work as expected in cats given Methimazole. That is 11% of all reports for this medicine, compared with 8.7% across reports for all cat medicines.

203Reports

33%Marked serious

13%Recovered

11%Died or euthanised

72 daysTypical onset

How soon it started

Same day

16 13%

1–2 days

2 1.6%

3–7 days

7 5.5%

1–4 weeks

21 17%

Over a month

81 64%

How the animals did

Recovered

24 12%

Recovered with lasting effects

3 1.5%

Still unwell when reported

56 28%

Died

10 4.9%

Euthanised

13 6.4%

Not known

97 48%

Problems reported at the same time

40 20%

32 16%

21 10%

20 9.9%

20 9.9%

17 8.4%

15 7.4%

11 5.4%

Age of the animals

Under 1 year

1–3 years

4–7 years

8–11 years

12+ years

165

About this medicine

Methimazole treats an overactive thyroid in cats.

Questions owners ask

Can Methimazole cause didn't work as expected in cats?: 203 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 72 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).

Didn't work as expected with similar medicines

Didn't work as expected after Velagliflozin (Senvelgo) 1,248 reports · 26% of its reports
Didn't work as expected after Bexagliflozin (Bexacat) 599 reports · 15% of its reports
Didn't work as expected after Insulin 1,967 reports · 52% of its reports

All reported side effects of Methimazole in cats · Medicines most reported with didn't work as expected