Study Overview: This study tests a medicine, DT120, for treating Major Depressive Disorder (MDD). MDD is a mental health condition that makes people feel very sad for a long time. The study has two parts: a 12-week period where neither the doctor nor the patient knows if they are getting DT120 or a placebo (a fake treatment), and a longer 40-week phase where everyone can get DT120 if needed.

Participation Details: To join, participants must be between 18 and 74 years old and have been diagnosed with MDD. They should have a high score on tests measuring depression severity, like the Montgomery-Åsberg Depression Rating Scale (MADRS) and the Clinical Global Impression-Severity (CGI-S) scale, which help understand how serious the depression is.

• Study length: 52 weeks total (12-week initial phase + 40-week extension).
• Participants may get DT120 treatment during the extension phase.
• Risks include possible side effects from DT120 and the need to meet specific health criteria.