Breathing problems after Levothyroxine in dogs

The FDA has received 248 reports of breathing problems in dogs after Levothyroxine. That is 8.2% of all reports for this medicine, compared with 2.7% across reports for all dog medicines, so it is reported unusually often with this medicine.

248Reports

69%Marked serious

31%Recovered

19%Died or euthanised

10 daysTypical onset

How soon it started

Same day

34 20%

1–2 days

22 13%

3–7 days

23 13%

1–4 weeks

21 12%

Over a month

71 42%

How the animals did

Recovered

66 27%

Recovered with lasting effects

11 4.4%

Still unwell when reported

55 22%

Died

21 8.5%

Euthanised

27 11%

Not known

68 27%

Problems reported at the same time

78 31%

66 27%

59 24%

51 21%

Restlessness or agitation

50 20%

Death

48 19%

Excessive thirst

41 17%

Overdose

35 14%

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 breathing problems in dogs?: 248 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 10 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).

Breathing problems with similar medicines

Breathing problems after Trilostane (Vetoryl) 771 reports · 6.5% of its reports
Breathing problems after Insulin 193 reports · 2.6% of its reports
Breathing problems after Phenylpropanolamine (Proin) 500 reports · 12% of its reports

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