Overdose after Levothyroxine in dogs

The FDA has received 184 reports of overdose in dogs after Levothyroxine. That is 6.1% of all reports for this medicine, compared with 1.3% across reports for all dog medicines, so it is reported unusually often with this medicine.

184Reports

51%Marked serious

39%Recovered

1.6%Died or euthanised

21 daysTypical onset

How soon it started

Same day

20 14%

1–2 days

4 2.9%

3–7 days

23 17%

1–4 weeks

37 27%

Over a month

54 39%

How the animals did

Recovered

68 37%

Recovered with lasting effects

3 1.6%

Still unwell when reported

29 16%

Euthanised

3 1.6%

Not known

81 44%

Problems reported at the same time

Didn't work as expected

41 22%

Elevated thyroxine (t4)

38 21%

35 19%

34 18%

26 14%

24 13%

23 13%

23 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 overdose in dogs?: 184 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 21 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).

Overdose with similar medicines

Overdose after Trilostane (Vetoryl) 76 reports · 0.6% of its reports
Overdose after Insulin 55 reports · 0.7% of its reports
Overdose after Phenylpropanolamine (Proin) 371 reports · 9.0% of its reports
Overdose after Velagliflozin (Senvelgo) 31 reports · 43% of its reports

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