While administering pills to cats is a challenge, these are so effective that the effort is worth it, and my cats have had no adverse reactions whatsoever, which I can't say about other flea products. (amazon.com)
This means that shampoos and other flea products containing certain insecticides should never be used on cats, although they may be fine for dogs. (pesthacks.com)
Additionally, while Advantage II doesn't contain permethrin, many other flea products do (such as Advantix II). (fleascience.com)