I was sick of Frontline and Advantage. They were beginning to lose effectiveness and I didn't like the weird, chemical smell and the way they made my kitties act. This is a great alternative, it really does weaken the fleas, I used it for 3 months straight and most of the fleas on my cats are gone. It didn't completely eradicate them, but combined with Capstar this is a safer program that does not harm kitties or people. It did not make my cats sick at all and the hardest part is getting them still long enough to squeeze the tube in their mouths. They would not touch their food when this was mixed in to it. My cats are pretty smart and figured out something was up so I did waste one tube but that's ok, live and learn.