This study looks at how a new medicine, called NMRA-335140, works for people with Major Depressive Disorder (MDD). MDD is a serious type of depression. In this study, some people will get the real medicine, and others will get a placebo, which is a pill that looks the same but has no medicine in it. This is called a "double-blind" study because neither the doctors nor the participants know who is getting the real medicine. The study lasts for up to 28 days of screening and 6 weeks of treatment. After 6 weeks, participants can join another study if they meet certain conditions.

Key Points:

• The study lasts up to 28 days for screening plus 6 weeks for treatment.
• Participants must have MDD symptoms for more than 4 weeks, but less than 12 months.
• You cannot join if you have certain other mental health issues or if you've recently been suicidal.