I bought this on the advice of my vet. The fleas in my area (eastern North Carolina) are apparently resistant to Frontline and other medications which use the same active ingredients, so even though I was treating her regularly with a topical, my dog got fleas at doggy daycare. After treating her with Capstar, a fast acting and effective but short term oral flea medication, I put this on her and we haven't seen any fleas since. I like that it lasts so long and I will definitely purchase this again.