**Study Summary** This research is exploring if a new medicine called *azetukalner* can help adults with Major Depressive Disorder (MDD), which is a type of depression. A *placebo* is a fake treatment that looks like the real one but doesn't have any medicine in it. This study is *randomized* (participants are randomly assigned to different groups), *double-blind* (neither doctors nor participants know who gets the medicine or placebo), and *controlled* (compares medicine to placebo). **Key Points to Consider:** - **Study Length:** The study will observe participants over time to see how well the medicine works and how safe it is. - **Eligibility:** You must be 18-74 years old, have experienced a major depressive episode before age 50, and meet specific medical criteria. - **Exclusion Criteria:** You cannot participate if you have certain mental health conditions, a recent history of substance abuse, or if you are pregnant or planning to become pregnant. This study is important for understanding new treatments for depression and could help improve the lives of many people. If you have questions, ask your doctor to see if this study might be right for you.