The purpose of this study is to compare DT-101 and placebo in adult participants with MDD. The study will also evaluate how safe and well tolerated the study drug is. The clinical study staff will check participants' suitability to take part in the clinical research study by performing physical and neurological examinations, obtaining blood and urine samples, conducting clinical assessments and reviewing medical and treatment history. These tests and assessments will continue throughout the study with the purpose of checking the participants' ongoing suitability and to collect data to analyze the effect that DT-101 may have on their depression symptoms. Participants will also have blood samples taken to allow analysis of how DT-101 is absorbed and used by the body (PK sampling), some blood samples may be retained in order to perform future research that may be useful when looking at whether genetics affects how a person responds to DT-101 (PGx sampling)
