This study is looking at how well a new drug, called DT-101, works for treating depression in adults. **Depression** is a mood disorder that causes a persistent feeling of sadness and loss of interest. The study compares DT-101 with a **placebo**, which looks like the real drug but has no active ingredient. Participants will visit the clinic every few weeks for health checks and to answer questions about how they're feeling. These visits will include physical and **neurological** (related to the brain and nerves) exams, blood and urine tests, and reviews of medical history. This helps to see if DT-101 is safe and how it affects depression symptoms. Some blood samples will help researchers understand how the drug is used by the body and may be saved for future studies on genetic effects.

• Participants must be 18-75 years old and have a history of depression.
• They cannot participate if they're pregnant or have certain medical conditions.
• Regular clinic visits are required, and some blood samples may be kept for future research.