Bests & Worsts Reviews from Amazon

Got this for my healthy 1-year-old cat after we moved into a flea-infested neighborhood. Administered one dose on his neck as directed. An hour later, he walks funny. Two hours later, his extremities twitch uncontrollably and he meows or hisses every time I touch him. Three hours later, he's essentially unable to move. Had to take him to the ER. The product I received from Amazon later turned out to be counterfeit. Now I buy the "same" product from the local humane society and my cat has been tolerating it just fine.