Blood problems after Levothyroxine in dogs

The FDA has received 104 reports of blood problems in dogs after Levothyroxine. That is 3.5% of all reports for this medicine, compared with 1.8% across reports for all dog medicines, so it is reported unusually often with this medicine.

104Reports

78%Marked serious

9.6%Recovered

40%Died or euthanised

60 daysTypical onset

How soon it started

Same day

6 11%

1–2 days

1 1.8%

3–7 days

6 11%

1–4 weeks

10 18%

Over a month

34 60%

How the animals did

Recovered

7 6.7%

Recovered with lasting effects

3 2.9%

Still unwell when reported

40 38%

Died

12 12%

Euthanised

30 29%

Not known

12 12%

Problems reported at the same time

46 44%

42 40%

40 38%

39 38%

27 26%

20 19%

20 19%

19 18%

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 blood problems in dogs?: 104 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 60 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).

Blood problems with similar medicines

Blood problems after Trilostane (Vetoryl) 252 reports · 2.1% of its reports
Blood problems after Insulin 89 reports · 1.2% of its reports
Blood problems after Phenylpropanolamine (Proin) 87 reports · 2.1% of its reports

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