This is a multicenter, randomized, double-blind, parallel-group, flexible dose, outpatient study evaluating the efficacy and safety of SEP-363856 flexibly dosed (50 - 75 mg/day) versus placebo over an 8-week Treatment Period in subjects with GAD. This study is projected to randomize approximately 434 subjects to 2 treatment groups (SEP-363856 [50 - 75 mg/day] or placebo) in a 1:1 ratio.~Approximately 30 additional subjects (N = 15 per treatment group) are projected to enroll in the Japan Cohort. Treatment assignment will be stratified by country. Study drug will be taken at approximately the same time each evening at bedtime .
A clinical study that will meaure how well SEP-363856 works and how safe it is in adults with Generalized Anixety Disorder. This study will be accepting both male and female subjects between the ages of 18 years and 65 years old. The study will be held in Approximately 50 global study centers and approximately 15 additional centers for a separate Japan population. Participation in the study can be up to approximately 12 weeks.