I bought Hartz Advanced Care Plus flea and tick drops for my 3 cats. We had been successfully using Frontline previouly with no adverse effects. This time I was a little short on cash so I tried the Hartz instead. I read the lable carefully and bought the smaller-cats/kittens size for my one tiny older cat and the regular (>10 lbs) size for my other two big fat cats. The two heavyweights are fine and bug-free. The little old lady cat is still very flexible and fastidious and was able (apparently) to get a taste of the medication. She was just listless (laid on the couch for most of 2 days–for her that’s not normal), had no appetite and kept swallowing for a couple of days and now she’s better, much to our relief. By the time we figured out that it might have been the flea drops, she was better. I can only imagine what would have happened if I had given her the regular size dose.