I have used Hartz Ultraguard Pro Flea and Tick Drops for cats on both of my cats for the past couple of moths and it seems to have kept the fleas at bay. The first one or two times I used them my cats seemed kind of lethargic after I put it on them, which seemed strange, but they seemed to come out of it within a day or so, so I didn’t worry much about. Last night I put it on them though and not only did they seem lethargic and like they didn’t feel good but today I noticed one of them shaking its back leg occasionally like she had something on it and also scratching the back of her head a lot. There wasn’t anything on her leg and both cats were still acting like they weren’t feeling good so I started Googling her symptoms and what might be going on. That is when I came across this blog and MANY reviews on other websites that indicated their cats had the same reaction. It is scary thinking that a product that has so many negative reviews and can cause these types of problems in cats, is still being sold! I am really hoping that my cats don’t have any long term effects. I think they are going to be ok but was so displeased with this, that I wanted to post something to warn others not to use this product at all! It is not worth the well being of your cat!