X-NOVA-OLE is a multicenter, open-label study to evaluate the long-term safety, tolerability, and efficacy of azetukalner as a monotherapy in adult participants who successfully completed an antecedent Phase 3 study of azetukalner in Major Depressive Disorder (MDD).

Inclusion Criteria:

• Participant successfully completed the treatment period of an antecedent azetukalner Phase 3 study in MDD.
• Participant provides written informed consent to participate in the study, is able to understand the procedures and study requirements, and agrees to abide by them.
• Participant is willing to comply with the contraception requirements.
• Male participants must agree not to donate sperm until 3 months after the last dose of study drug. Female participants must agree not to donate ova until 3 months after the last dose of study drug.

Exclusion Criteria:

• Participant met any of the withdrawal criteria, or discontinued study drug early, or was terminated early from an antecedent study.
• Participant had any protocol deviations in an antecedent azetukalner study that, in the opinion of the investigator, would preclude participation in this study.
• Participant is unable to comply with study procedures or is inappropriate for the study, as judged by the investigator.
• Participant has any medical condition, personal circumstance, or ongoing AE (from an antecedent study) that, in the opinion of the investigator, exposes the participant to unacceptable risk by participating in the study or prevents adherence to the protocol.
• Female participant who is pregnant, breastfeeding, or planning to become pregnant within 3 months after the last dose of study drug.
• Participant is planning to enter a clinical study with a different investigational drug or planning to use any experimental device for treatment of any medical condition during the study or within 28 days after completion of this study.
• Participant is judged to have a significant risk for self-harm or suicidal behavior or is considered to be an imminent danger to themself or others, as determined by the C-SSRS or in the opinion of the investigator.