The study has two parts which enroll separately from each other such that participants may choose to participate in either but not both: the main study and a study addendum.
* The main study includes a 3-month, randomized, double-blind treatment period in which participants receive either galcanezumab or placebo, followed by a 9-month open-label extension in which all participants receive galcanezumab.
* The study addendum is a stand-alone study of galcanezumab pharmacokinetics and safety in a group of participants separate from those in the main study. The study addendum includes a 5-month evaluation period after a single injection of galcanezumab, followed by a 9-month open-label extension.
