Mast cell tumour after Diphenhydramine in dogs

The FDA has received 32 reports of mast cell tumour in dogs after Diphenhydramine. That is 0.7% of all reports for this medicine, compared with 0.0% across reports for all dog medicines, so it is reported unusually often with this medicine.

32Reports

66%Marked serious

19%Recovered

3.1%Died or euthanised

14 daysTypical onset

How soon it started

Same day

2 8.3%

1–2 days

1 4.2%

3–7 days

5 21%

1–4 weeks

6 25%

Over a month

10 42%

How the animals did

Recovered

4 13%

Recovered with lasting effects

2 6.3%

Still unwell when reported

11 34%

Died

1 3.1%

Not known

14 44%

Problems reported at the same time

Didn't work as expected

20 63%

Swelling

20 63%

Injection site reaction

16 50%

Mass

7 22%

Lethargy

6 19%

Lipoma

6 19%

Skin redness

6 19%

Hair loss

6 19%

Age of the animals

Under 1 year

1–3 years

4–7 years

8–11 years

12+ years

About this medicine

Type: medicine.

Questions owners ask

Can Diphenhydramine cause mast cell tumour in dogs?: 32 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 14 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).

Mast cell tumour with similar medicines

Mast cell tumour after Butorphanol 24 reports · 0.5% of its reports
Mast cell tumour after Famotidine 26 reports · 1.0% of its reports
Mast cell tumour after Tigilanol Tiglate 46 reports · 2.3% of its reports

All reported side effects of Diphenhydramine in dogs · Medicines most reported with mast cell tumour