Low blood pressure after Diphenhydramine in dogs

The FDA has received 41 reports of low blood pressure in dogs after Diphenhydramine. That is 0.9% 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.

41Reports

98%Marked serious

20%Recovered

44%Died or euthanised

Same dayTypical onset

How soon it started

Same day

23 66%

1–2 days

2 5.7%

3–7 days

2 5.7%

1–4 weeks

3 8.6%

Over a month

5 14%

How the animals did

Recovered

8 20%

Still unwell when reported

14 34%

Died

9 22%

Euthanised

9 22%

Not known

1 2.4%

Problems reported at the same time

29 71%

27 66%

24 59%

19 46%

19 46%

18 44%

17 41%

14 34%

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 low blood pressure in dogs?: 41 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 the same day 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 blood pressure with similar medicines

Low blood pressure after Butorphanol 26 reports · 0.6% of its reports
Low blood pressure after Propofol 22 reports · 0.7% of its reports
Low blood pressure after Isoflurane 28 reports · 1.0% of its reports
Low blood pressure after Midazolam 20 reports · 1.7% of its reports
Low blood pressure after Fentanyl 20 reports · 3.2% of its reports

All reported side effects of Diphenhydramine in dogs · Medicines most reported with low blood pressure