Allergic reaction after Levothyroxine in dogs

57 reports to the FDA describe allergic reaction in dogs given Levothyroxine. That is 1.9% of all reports for this medicine, compared with 2.3% across reports for all dog medicines.

57Reports

67%Marked serious

32%Recovered

5.3%Died or euthanised

3 daysTypical onset

How soon it started

Same day

19 45%

1–2 days

2 4.8%

3–7 days

7 17%

1–4 weeks

7 17%

Over a month

7 17%

How the animals did

Recovered

17 30%

Recovered with lasting effects

1 1.8%

Still unwell when reported

17 30%

Died

1 1.8%

Euthanised

2 3.5%

Not known

19 33%

Problems reported at the same time

21 37%

15 26%

11 19%

9 16%

9 16%

8 14%

7 12%

7 12%

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 allergic reaction in dogs?: 57 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 3 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).

Allergic reaction with similar medicines

Allergic reaction after Trilostane (Vetoryl) 53 reports · 0.4% of its reports
Allergic reaction after Insulin 52 reports · 0.7% of its reports
Allergic reaction after Phenylpropanolamine (Proin) 63 reports · 1.5% of its reports

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