I am sure Frontline didn't not work on my 3 beautiful kitties. the mum has long black thick haired and suffered terribly. i felt she passed them onto her 2 babies. I have now found Advantage at petfleas.com for £9.36 for 4 pipettes. no postage. its £19.00 at pets at home plus postage. its been a life saver for us. it worked instantly. it does not need prescription either. I haven't seem any of them scratch since I started using it.