A Randomized Study of Azetukalner Versus Placebo in Major Depressive Disorder (X-NOVA3)

Key Inclusion Criteria:

* Adults ≥18 and ≤74 years of age and experienced their first major depressive episode (MDE) prior to 50 years of age
* Body Mass Index (BMI) ≤40 kg/m2
* Meets the Diagnostic and Statistical Manual of Mental Disorders Fifth Edition Text Revised (DSM-5-TR) criteria for current major depressive disorder and is currently in an MDE, confirmed using the Mini International Neuropsychiatric Interview (MINI)
* Participant's current MDE has a duration of ≥6 weeks and ≤24 months.

Key Exclusion Criteria:

* Participant has a primary diagnosis of a mood disorder other than MDD.
* Participant has a history of any of the following: MDD with psychotic or catatonic features; MDD with mixed features; Bipolar I or II disorder; Obsessive-compulsive disorder; Schizophrenia, primary thought disorder, or other psychotic disorder.
* Participant has a current diagnosis of any of the following: MDD with seasonal pattern; Depression with peripartum or perimenopausal onset; Post traumatic stress disorder; Antisocial or borderline personality disorder (or presence of clinically significant borderline personality traits); Panic disorder and/or agoraphobia; ADHD treated with a psychostimulant, diagnosed during the current MDE, or with unstable symptoms, as judged by the investigator.
* Participant has a substance (excluding tobacco) or alcohol use disorder within the 12 months prior to screening.
* Participant has had an active suicidal plan/intent within the 6 months prior to screening, presence of suicidal behavior in the last 2 years, or \>1 suicide attempt \> 24 years of age.
* Participant has a history of non-suicidal self-harm behavior in the 12 months prior to screening.
* Participant has used antidepressants or other prohibited medications (including benzodiazepines), within the 2 weeks (4 weeks for fluoxetine) or within a period less than 5 times the drug's half-life, whichever is longer, prior to randomization.
* Participant has a history of non-response to ≥2 antidepressant drugs of adequate dose and duration in the current MDE as determined by the Antidepressant Treatment Response Questionnaire (ATRQ).
* Participants with medical conditions that may interfere with the purpose or conduct of the study
* Participant is pregnant, breastfeeding, or planning to become pregnant.