This is a global, phase 3, randomized, double-blind, parallel-group, 2-arm, placebo controlled, multicenter trial designed to compare the efficacy, safety and tolerability of a fixed dose of SEP-363856 (75 millligrams per day \[mg/day\]) to placebo over an 8-week double-blind treatment period in adults with generalized anxiety disorder (GAD).
Male or female participants at least 18 years of age at the time of informed consent
Primary diagnosis of 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) 18-40 kilograms per square meter (kg/m²)
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)