A Randomized Study of Azetukalner Versus Placebo in Depressive Episodes Associated With Bipolar I or II Disorder (Bipolar Depression)

Key Inclusion Criteria: * Adults ≥18 and ≤74 years of age who experienced their first major depressive episode (MDE) prior to 50 years of age. * Body Mass Index (BMI) ≥18 kg/m2 and ≤40 kg/m2. * Meets the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, Text Revision (DSM-5-TR) criteria for bipolar I or II disorder and is currently in a MDE, confirmed using the Mini International Neuropsychiatric Interview (MINI). * Current MDE must has a duration of ≥4 weeks and ≤12 months. Key Exclusion Criteria: * Participant has any type of major depressive disorder (MDD) diagnosis, including MDD with psychotic features, MDD with catatonia, MDD with seasonal pattern, or postpartum depression. * Participant has any nonbipolar psychiatric diagnosis. * Participant has a substance use disorder (excluding tobacco) within the 6 months prior to screening visit. * Participant has a symptomatic eating disorder within the 12 months prior to screening visit. * Participant has a Young Mania Rating Scale (YMRS) score \>12 points at screening visit or randomization. * Participant has been hospitalized for mania within the 30 days prior to screening visit. * Participant is considered treatment-resistant in the current bipolar depressive episode, defined as having treatment resistance (no remission) to ≥2 different medications approved by the regional regulatory authority at an adequate dose (per regulatory approved label) and for an adequate duration (at least 6 weeks). * Participant has had an active suicidal plan/intent within the 6 months prior to screening, presence of suicidal behavior in the last 12 months. * Participant has self-injurious behavior without intent to die in the 12 months prior to screening. * Participant has used antidepressants, mood stabilizers, anticonvulsants, antipsychotics, or other prohibited medications within the 1 week or within a period less than 5 times the drug's half-life, whichever is longer prior to randomization. * Participants with medical conditions that may interfere with the purpose or conduct of the study. * Participant is pregnant, breastfeeding, or planning to become pregnant.