Low thyroxine (t4) after Levothyroxine in dogs

87 reports to the FDA describe low thyroxine (t4) in dogs given Levothyroxine. That is 2.9% of all reports for this medicine, compared with 0.1% across reports for all dog medicines, so it is reported unusually often with this medicine.

87Reports

39%Marked serious

24%Recovered

9.2%Died or euthanised

37 daysTypical onset

How soon it started

Same day

3 5.5%

1–2 days

2 3.6%

3–7 days

1 1.8%

1–4 weeks

14 25%

Over a month

35 64%

How the animals did

Recovered

20 23%

Recovered with lasting effects

1 1.1%

Still unwell when reported

16 18%

Died

2 2.3%

Euthanised

6 6.9%

Not known

42 48%

Problems reported at the same time

Didn't work as expected

54 62%

26 30%

14 16%

13 15%

12 14%

Elevated thyroxine (t4)

12 14%

Weight loss

11 13%

Kidney problems

11 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 low thyroxine (t4) in dogs?: 87 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 37 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).

Low thyroxine (t4) with similar medicines

Low thyroxine (t4) after Trilostane (Vetoryl) 112 reports · 0.9% of its reports

All reported side effects of Levothyroxine in dogs · Medicines most reported with low thyroxine (t4)