This is a global Phase 2b/3 study to evaluate the safety and effectiveness of an
investigational study drug (called PF-06651600) in adults and adolescents (12 years and
older) who have 50% or greater scalp hair loss. The study is placebo-controlled, meaning that
some patients entering the study will not receive active study drug but will receive tablets
with no active ingredients (a placebo). This is a dose-ranging study, investigating 5
different dosing regimens. It will be double-blinded, meaning that the sponsor, the study
doctors, the staff, and the patients will not know whether a patient is on active study drug
(or the dose) or placebo.