Lethargy after Methimazole in cats

311 reports to the FDA describe lethargy in cats given Methimazole. That is 17% of all reports for this medicine, compared with 14% across reports for all cat medicines.

311Reports

57%Marked serious

18%Recovered

22%Died or euthanised

18 daysTypical onset

How soon it started

Same day

39 16%

1–2 days

28 11%

3–7 days

16 6.5%

1–4 weeks

81 33%

Over a month

81 33%

How the animals did

Recovered

54 17%

Recovered with lasting effects

1 0.3%

Still unwell when reported

83 27%

Died

32 10%

Euthanised

35 11%

Not known

106 34%

Problems reported at the same time

200 64%

107 34%

64 21%

64 21%

48 15%

47 15%

41 13%

35 11%

Age of the animals

Under 1 year

1–3 years

4–7 years

8–11 years

12+ years

235

About this medicine

Methimazole treats an overactive thyroid in cats.

Questions owners ask

Can Methimazole cause lethargy in cats?: 311 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 18 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).

Lethargy with similar medicines

Lethargy after Velagliflozin (Senvelgo) 639 reports · 13% of its reports
Lethargy after Bexagliflozin (Bexacat) 483 reports · 12% of its reports
Lethargy after Insulin 472 reports · 13% of its reports

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