Bayer is the best source to go for the formula details; they made the product, after all. I have used dog Advantage on cats; in fact it's easier to more precisely dose by body weight than the rather crude 0.4 cc for under 9 lbs and 0.8 cc for over 9 lbs. It would be reasonable to suspect that a 8.9 lb cat could be underdosed, or a 9.1 cat overdosed. Raven was just over 9 lbs, and drooled after I applied the product, but showed no further effects (she may have licked another cat who had it on.)