Underdose after Levothyroxine in dogs

The FDA has received 71 reports of underdose in dogs after Levothyroxine. That is 2.4% 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.

71Reports

37%Marked serious

15%Recovered

1.4%Died or euthanised

77 daysTypical onset

How soon it started

Same day

3 7.3%

1–2 days

3 7.3%

3–7 days

2 4.9%

1–4 weeks

5 12%

Over a month

28 68%

How the animals did

Recovered

10 14%

Recovered with lasting effects

1 1.4%

Still unwell when reported

16 23%

Died

1 1.4%

Not known

43 61%

Problems reported at the same time

Didn't work as expected

32 45%

11 15%

10 14%

10 14%

9 13%

7 9.9%

6 8.5%

6 8.5%

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 underdose in dogs?: 71 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 77 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).

Underdose with similar medicines

Underdose after Trilostane (Vetoryl) 1,431 reports · 12% of its reports
Underdose after Insulin 86 reports · 1.2% of its reports
Underdose after Phenylpropanolamine (Proin) 316 reports · 7.6% of its reports

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