A Trial of the Efficacy and Safety of Fixed Doses of SEP-363856 in Adults With Generalized Anxiety Disorder

Key Inclusion Criteria

• 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/m\^2) (inclusive)
• Participant is willing and able to comply with study procedures and visit schedule
• Medically stable as determined by medical history, physical exam, vital signs, and laboratory tests
• Willing and able to discontinue prohibited medications/therapies per protocol
• i) Females of childbearing potential: negative pregnancy test and agreement to use acceptable contraception ii) Males: agreement to follow protocol-defined contraception and reproductive restrictions
• Participant is willing and able to safely discontinue all prohibited medications/therapies/herbal supplements in accordance with the protocol-required washouts prior to baseline/Day 1 and during the trial period.

Key Exclusion Criteria

• 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)
• Use of prohibited medications/therapies within protocol-defined timeframes (e.g., certain antipsychotics, mood stabilizers, benzodiazepines, investigational treatments)
• Prior exposure to restricted treatments
• Pregnant or breastfeeding females
• Participation in another investigational study within 180 days (or more than [>] 1 trial in last year)
• Known history of human immunodeficiency virus seropositivity, hepatitis B or C