This study involves people who have Major Depressive Disorder, a condition where a person experiences persistent feelings of sadness and loss of interest in activities that affects daily life. The study will test a medication called Ulotaront, also known by its code name SEP-363856, which will be given as an additional treatment alongside standard antidepressant medications. The antidepressants that may be used in this study include venlafaxine, citalopram, sertraline, duloxetine, fluoxetine, and paroxetine. Some people in the study will receive placebo instead of the study medication. The purpose of this study is to find out if SEP-363856 works better than placebo when added to standard antidepressant treatment in helping people whose depression has not improved enough with their current antidepressant medication.
The study is divided into two phases and lasts for about 14 weeks in total. During the first phase, which lasts 8 weeks, all people in the study will receive one of the standard antidepressant medications mentioned above. This phase helps to confirm that the depression has not improved enough with the antidepressant alone. During the second phase, which lasts 6 weeks, people will continue taking their antidepressant medication and will also receive either SEP-363856 or placebo. All medications are taken by mouth. The study will measure changes in depression symptoms using rating scales that assess mood, daily functioning, and overall well-being.
Throughout the study, regular check-ups will be conducted to monitor safety. These check-ups include physical examinations, measurements of body weight, blood pressure, heart rate, and body temperature. Blood and urine samples will be collected to check general health and how the body is processing the medications. Heart activity will be monitored using a test that records the electrical signals of the heart. The study will also assess other aspects such as movement-related side effects, sleep quality, sexual functioning, and thoughts about self-harm. People in the study will be asked about any unwanted effects they may experience.



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