Bests & Worsts Reviews from Amazon

I used Advantage II for the first time on my cat and within hours the fur on the back of her neck fell out. It's been 3 days and she has a bloody, bald patch of skin. I've taken her to the vet twice now and spent over $600 trying to help with the pain and discomfort. She has never had this type of reaction to the previous formula. I feel awful for putting this on her, and after seeing other reviews I realize this has happened to other users. Unfortunately this product is non-returnable so it was an expensive mistake and an awful experience for my cat.