We used the Hartz flea and tick drops on our cat Oreo. The next day my husband came home for lunch and found my cat shaking and she could not even walk. she was trying to lick her paw and she was trembling so bad she could not even get it up to her mouth. we took her to the vet luckily she survived but she had to stay overnight and had to be given lots of fluids and medication for the tremors. she is fine now but she has lost a little of her spunk.They should at least have a warning label on the package if they will not take it off the shelves.but i think they should take it off the shelves before it hurts more cats. i thought my cat was going to die. dont ever use this product because it can seriously damage your cat if not kill it.