Hair loss after Methimazole in cats

The FDA has received 114 reports of hair loss in cats after Methimazole. That is 6.4% of all reports for this medicine, compared with 14% across reports for all cat medicines, so it is reported less often than average with this medicine.

114Reports

47%Marked serious

18%Recovered

3.5%Died or euthanised

27 daysTypical onset

How soon it started

Same day

6 7.4%

1–2 days

10 12%

3–7 days

9 11%

1–4 weeks

18 22%

Over a month

38 47%

How the animals did

Recovered

20 18%

Still unwell when reported

49 43%

Died

2 1.8%

Euthanised

2 1.8%

Not known

41 36%

Problems reported at the same time

Itching

54 47%

Skin rash or irritation

26 23%

18 16%

11 9.6%

10 8.8%

10 8.8%

10 8.8%

10 8.8%

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 hair loss in cats?: 114 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 27 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).

Hair loss with similar medicines

Hair loss after Velagliflozin (Senvelgo) 35 reports · 0.7% of its reports
Hair loss after Bexagliflozin (Bexacat) 34 reports · 0.8% of its reports
Hair loss after Insulin 80 reports · 2.1% of its reports

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