Hair loss after Fipronil in cats

The FDA has received 34 reports of hair loss in cats after Fipronil. That is 6.8% of all reports for this medicine, compared with 14% across reports for all cat medicines, so it is reported less often than average with this medicine.

34Reports
50%Marked serious
21%Recovered
2.9%Died or euthanised
8 daysTypical onset
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How soon it started

Same day
4 15%
1–2 days
3 12%
3–7 days
5 19%
1–4 weeks
5 19%
Over a month
9 35%

How the animals did

Recovered
7 21%
Still unwell when reported
7 21%
Euthanised
1 2.9%
Not known
19 56%

Problems reported at the same time

Application site reaction
15 44%
11 32%
Skin redness
6 18%
Dry skin
5 15%
Didn't stop worms
5 15%
Skin rash or irritation
4 12%
Eye disorder (for photophobia see 'neurological')
4 12%

Age of the animals

Under 1 year
2
1–3 years
8
4–7 years
5
8–11 years
7
12+ years
11

About this medicine

Fipronil kills fleas and ticks (spot-on).

Questions owners ask

Can Fipronil cause hair loss in cats?
34 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 8 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).

Hair loss with similar medicines

All reported side effects of Fipronil in cats · Medicines most reported with hair loss