Hair loss after Levothyroxine in dogs

The FDA has received 108 reports of hair loss in dogs after Levothyroxine. That is 3.6% of all reports for this medicine, compared with 1.0% across reports for all dog medicines, so it is reported unusually often with this medicine.

108Reports

60%Marked serious

24%Recovered

5.6%Died or euthanised

30 daysTypical onset

How soon it started

Same day

4 4.9%

1–2 days

7 8.5%

3–7 days

8 9.8%

1–4 weeks

24 29%

Over a month

39 48%

How the animals did

Recovered

21 19%

Recovered with lasting effects

5 4.6%

Still unwell when reported

28 26%

Euthanised

6 5.6%

Not known

48 44%

Problems reported at the same time

Itching

38 35%

Skin rash or irritation

27 25%

22 20%

20 19%

17 16%

17 16%

15 14%

15 14%

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 hair loss in dogs?: 108 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 30 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 Trilostane (Vetoryl) 380 reports · 3.2% of its reports
Hair loss after Insulin 92 reports · 1.3% of its reports
Hair loss after Phenylpropanolamine (Proin) 38 reports · 0.9% of its reports

All reported side effects of Levothyroxine in dogs · Medicines most reported with hair loss