I've used it on about 20 cats at various times and never had a bad reaction.

The one time I had a bad reaction was with BioSpot. The cat was acting like he was having seizures, trying to rub the back of his neck on the floor, and mrowing horribly. I managed to wash most of it off with a wet cloth and he was fine. Never put anything on that particular cat again.

I also use Revolution on my dogs, different formula however.

Mary