I use to buy this product online somewhere and it worked the first two times I bought it and then the next time I bought it, it did NOT work at all. My dog was ate up with fleas and we did everything. Then my cousin goes in half with me and buys Advantix and instead of putting it right behind his neck, he put it there and all the was down his back but to where the dog couldn't reach to lick it and his poor thighs were infested with fleas and they all went away and they haven't been back since and I don't want them back but that stuff is so expensive I'm going to have to borrow money to buy some with because you have to have it. Advantix killed the fleas, got rid of them and kept them from coming back and it also kept the ticks off of him. He did not bring in a tick once this year, when they were out and I never had to get any off of him because that Advantix protected him.