First introduced in the U.S. by a dermatologic surgeon in 1991, botulinum toxin injections are used primarily to paralyze certain facial muscles which cause frown lines, crows feet and other lines of dynamic facial expression. The 3 medications used in the practice are Botox, Dysport and Xeomin, all with similar functions and mechanisms of action. They work by relaxing the underlying facial muscles that help form wrinkles, an effect that lasts for three to four months. Botox can also be use to improve neck lines and to control excessive sweating.