I put this on my cat 4 times over a 4 month period. (He is a healthy 3 year old) Each time, he reacted more negatively than the time before. Last dose, he acted as if it was stinging him, and he was aggressive and in a bad mood for 2 days. I looked up information regarding counterfeit flea meds and although the vials do have the right wording--the epa # on the vials is one of two epa #'s that have been counterfeited. I am not taking anymore chances with the last two vials. I am throwing it out. Guess I will have to buy from a more reputable source in order to feel safe about this.