I bought Hartz Ultraguard Flea and Tick drops from Wal-mart. Both cats have not been treated for fleas in over 2 years and I noticed a couple small scabs on them which indicates fleas. The 7 year old female is fine, skin clear, no problems. My 16 year old female has resorted to scratching wildly at the door to get out, has been non-stop meowing no matter what we do. I have seen her drink and she is using the litter box as normal, but she will not eat her can food (which she loves). It has been 2 1/2 weeks since the application, so I know it is in her system now. I was told since she is not having seizure activity and she is still eating/drinking to basically let it run out of her body (about a week it should be out). I will NEVER but Hartz again.