Weakness after Levothyroxine in dogs

144 reports to the FDA describe weakness in dogs given Levothyroxine. That is 4.8% of all reports for this medicine, compared with 1.4% across reports for all dog medicines, so it is reported unusually often with this medicine.

144Reports

80%Marked serious

16%Recovered

27%Died or euthanised

28 daysTypical onset

How soon it started

Same day

7 6.9%

1–2 days

12 12%

3–7 days

10 9.8%

1–4 weeks

23 23%

Over a month

50 49%

How the animals did

Recovered

18 13%

Recovered with lasting effects

5 3.5%

Still unwell when reported

52 36%

Died

9 6.3%

Euthanised

30 21%

Not known

30 21%

Problems reported at the same time

58 40%

43 30%

40 28%

35 24%

34 24%

31 22%

28 19%

21 15%

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 weakness in dogs?: 144 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 28 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).

Weakness with similar medicines

Weakness after Trilostane (Vetoryl) 851 reports · 7.1% of its reports
Weakness after Insulin 238 reports · 3.2% of its reports
Weakness after Phenylpropanolamine (Proin) 140 reports · 3.4% of its reports

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