Lethargy after Ondansetron in cats

The FDA has received 72 reports of lethargy in cats after Ondansetron. That is 33% of all reports for this medicine, compared with 14% across reports for all cat medicines, so it is reported unusually often with this medicine.

72Reports
76%Marked serious
21%Recovered
24%Died or euthanised
3 daysTypical onset
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How soon it started

Same day
14 22%
1–2 days
13 20%
3–7 days
11 17%
1–4 weeks
15 23%
Over a month
12 18%

How the animals did

Recovered
15 21%
Still unwell when reported
25 35%
Died
7 9.7%
Euthanised
10 14%
Not known
15 21%

Problems reported at the same time

Age of the animals

Under 1 year
8
1–3 years
7
4–7 years
14
8–11 years
14
12+ years
29

About this medicine

Type: medicine.

Questions owners ask

Can Ondansetron cause lethargy in cats?
72 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).

Lethargy with similar medicines

All reported side effects of Ondansetron in cats · Medicines most reported with lethargy