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.

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 .

Inclusion Criteria: (list is not all inclusive)

• Male or female subject between 18 to 65 years of age.
• Subject meets DSM-5 criteria for a diagnosis of Generalized Anxiety Disorder.
• Subject must be willing and able to comply with the study procedures and visit schedule and must be able to understand and follow verbal and written instructions.

Exclusion Criteria: (list is not all inclusive)

• Subject has DSM-5-based diagnosis of any disorder other than Generalized Anxiety Disorder that was the primary focus of treatment within 12 months before Screening.
• Subjects who report an inadequate response to more than 3 antidepressant treatments
• Subject is at significant risk of harming self or others based on Investigator's judgment.
• Subject has any clinically significant unstable medical condition or any clinically significant chronic disease that in the opinion of the Investigator, would limit the subject's ability to complete and/or participate in the study.
• Female subject who is pregnant, lactating, or plans to get pregnant during the study.

Anonymized Individual participant data (IPD) that underlie the results of this study will be shared with researchers to achieve aims pre-specified in a methodologically sound research proposal. Small studies with less than 25 participants are excluded from data sharing.

Data will be available after marketing approval in global markets, or beginning 1-3 years following article publication. There is no end date to the availability of the data.

Otsuka will share data on the Vivli data sharing platform which can be found here: https://vivli.org/ourmember/Otsuka/

double blind