Behaviour change after Fipronil + S-methoprene (Frontline Plus) in dogs

The FDA has received 181 reports of behaviour change in dogs after Fipronil + S-methoprene. That is 6.1% of all reports for this medicine, compared with 2.5% across reports for all dog medicines, so it is reported unusually often with this medicine.

181Reports

61%Marked serious

54%Recovered

3.9%Died or euthanised

38 daysTypical onset

How soon it started

Same day

15 16%

1–2 days

7 7.5%

3–7 days

7 7.5%

1–4 weeks

13 14%

Over a month

51 55%

How the animals did

Recovered

96 53%

Recovered with lasting effects

2 1.1%

Still unwell when reported

10 5.5%

Died

4 2.2%

Euthanised

3 1.7%

Not known

66 36%

Problems reported at the same time

Lethargy

44 24%

Restlessness or agitation

34 19%

31 17%

30 17%

24 13%

21 12%

16 8.8%

14 7.7%

Age of the animals

Under 1 year

1–3 years

4–7 years

8–11 years

12+ years

About this medicine

Fipronil kills fleas and ticks (spot-on).

Products with this combination include Frontline Plus. The FDA hides brand names in its public data, so these reports cover every product with the same active ingredients.

Questions owners ask

Can Fipronil + S-methoprene cause behaviour change in dogs?: 181 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 38 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).

Behaviour change with similar medicines

Behaviour change after Spinosad (Comfortis) 1,176 reports · 2.1% of its reports
Behaviour change after Lufenuron + Milbemycin Oxime (Sentinel) 358 reports · 1.4% of its reports
Behaviour change after Imidacloprid + Moxidectin (Advantage Multi) 1,205 reports · 9.2% of its reports
Behaviour change after Nitenpyram (Capstar) 323 reports · 3.0% of its reports
Behaviour change after Lufenuron + Milbemycin Oxime + Praziquantel (Sentinel Spectrum) 128 reports · 1.3% of its reports
Behaviour change after Flumethrin + Imidacloprid (Seresto) 167 reports · 7.3% of its reports
Behaviour change after Imidacloprid 94 reports · 4.9% of its reports
Behaviour change after Fipronil 66 reports · 4.7% of its reports
Behaviour change after Lufenuron 20 reports · 2.0% of its reports
Behaviour change after Imidacloprid + Permethrin + Pyriproxyfen 70 reports · 9.5% of its reports

All reported side effects of Fipronil + S-methoprene in dogs · Medicines most reported with behaviour change