I had Botox three times with great results, but the fourth time - nothing. It simply stopped working. My dermatologist - board certified, very reputable - invited me into his private office and called Allergan's representative on his speakerphone with me present, and Allergan's rep said about 10% of all cosmetic patients eventually become immune to it and it will never work again. The doctor did inject me three more times over the next two months for free, each time with a fresh vial of Botox, but there were never any results. I then tried two other board-certified dermatologist and once again, nothing. I wish Botox would work for me again, because it was great when it did.