Didn't work as expected after Levothyroxine in dogs

421 reports to the FDA describe didn't work as expected in dogs given Levothyroxine. That is 14% of all reports for this medicine, compared with 13% across reports for all dog medicines.

421Reports

29%Marked serious

12%Recovered

3.1%Died or euthanised

67 daysTypical onset

How soon it started

Same day

24 12%

1–2 days

8 3.9%

3–7 days

3 1.5%

1–4 weeks

35 17%

Over a month

135 66%

How the animals did

Recovered

40 9.5%

Recovered with lasting effects

11 2.6%

Still unwell when reported

133 32%

Died

4 1.0%

Euthanised

9 2.1%

Not known

224 53%

Problems reported at the same time

54 13%

42 10.0%

41 9.7%

37 8.8%

35 8.3%

32 7.6%

27 6.4%

26 6.2%

Age of the animals

Under 1 year

1–3 years

4–7 years

8–11 years

170

12+ years

145

About this medicine

Levothyroxine treats an underactive thyroid.

Questions owners ask

Can Levothyroxine cause didn't work as expected in dogs?: 421 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 67 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 Trilostane (Vetoryl) 1,750 reports · 15% of its reports
Didn't work as expected after Insulin 3,834 reports · 52% of its reports
Didn't work as expected after Phenylpropanolamine (Proin) 702 reports · 17% of its reports

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