I had to use Comfortis last yr, when I could not get rid of the fleas after trying natural products. It worked great, though I was not happy with giving it to my 3. I actually gave a whole one to the one (10 lbs) with the most fleas and then split one for the other two (10 & 5 lbs) and I never saw another flea after that day. So I was happy
and so were they not having to stop and scratch every few seconds.