I bought the Hartz flea and tick meds to try on my two cats last year during the flea season. The first month I put it on them, they started shaking violently after about two hours. I bathed both of my cats and I called the 1-800 number on the Hartz box and they said it couldn’t possibly be their product, to please try it again and let them know. So, me being the fool that I can be, tried putting it on them again, and once again, they started shaking violently, and also started with the most horrific howling sound I have every heard from a cat…..like they were in severe pain. So again, I washed off the product and called Hartz and they STILL claimed that it couldn’t be THEIR product. Well, I threw the remainder of the product in the garbage and went back to the prescription flea meds that I used prior to trying Hartz brand. NEVER AGAIN!