This is a global, phase 3, randomized, double-blind, parallel-group, 3-arm, placebo-controlled, multicenter study designed to compare the efficacy, safety, and tolerability of fixed doses of SEP-363856 (50 and 75 milligrams per day \[mg/day\]) to placebo in adults at least 18 years of age with generalized anxiety disorder (GAD) over 8 weeks.
Male or female participants at least 18 years of age at the time of informed consent
Primary diagnosis of Generalized Anxiety Disorder (GAD) per Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), confirmed by Mini-International Neuropsychiatric Interview (MINI) and clinical psychiatric evaluation
Body Mass Index (BMI) between 18 and 40 kilograms per square meter (kg/m²) (inclusive)
Participant is willing and able to comply with study procedures and visit schedule
Current DSM-5 diagnosis of major depressive episode, post traumatic stress disorder (PTSD), or any psychiatric disorder other than GAD that was the primary focus of treatment within 12 months prior to screening
Substance use disorder (excluding nicotine/caffeine) within 12 months prior to screening
Lifetime history of certain psychiatric disorders (e.g., schizophrenia spectrum disorders, bipolar disorder, obsessive-compulsive disorder, borderline or antisocial personality disorder)
Significant suicide risk (e.g., recent suicidal behavior/ideation per Columbia-Suicide Severity Rating Scale [C-SSRS] or MADRS)