Loose stool after Levothyroxine in dogs

The FDA has received 55 reports of loose stool in dogs after Levothyroxine. That is 1.8% of all reports for this medicine, compared with 0.9% across reports for all dog medicines, so it is reported unusually often with this medicine.

55Reports

47%Marked serious

29%Recovered

13%Died or euthanised

12 daysTypical onset

How soon it started

Same day

6 19%

1–2 days

2 6.5%

3–7 days

4 13%

1–4 weeks

8 26%

Over a month

11 35%

How the animals did

Recovered

12 22%

Recovered with lasting effects

4 7.3%

Still unwell when reported

13 24%

Died

3 5.5%

Euthanised

4 7.3%

Not known

19 35%

Problems reported at the same time

24 44%

20 36%

19 35%

13 24%

12 22%

Didn't work as expected

11 20%

Diarrhea

9 16%

Death

7 13%

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 loose stool in dogs?: 55 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 12 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).

Loose stool with similar medicines

Loose stool after Trilostane (Vetoryl) 231 reports · 1.9% of its reports
Loose stool after Insulin 54 reports · 0.7% of its reports
Loose stool after Phenylpropanolamine (Proin) 52 reports · 1.3% of its reports

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