We gave one dose of this product to our cat 5 days ago. Other than the fleas we were treating him for, he was an otherwise perfectly healthy, active cat. 2 days ago, he became somewhat lethargic, but we had been told flea medications can sometimes make pets feel a bit ill initially, so we assumed that’s all it was. Today he rapidly worsened, started having trouble breathing, and died on the way to the animal hospital. I wish I had thought to google this product before ever trying it, but you assume if it’s for sale across national retailers and it’s a name you recognize, that it must be safe.