In this study, researchers will learn more about a study drug called DT-101 in participants with Major Depressive Disorder (MDD), a form of depression. The goal of this clinical trial is to learn if DT-101 can treat depression in adults. The effect of DT-101 will be compared to placebo. A placebo looks the drug but contains no medicine. Subjects will attend the clinic for complete general health checks and to complete questionnaires.

The purpose of this study is to compare DT-101 and placebo in adult participants with MDD already receiving medication for depression. The clinical study will also evaluate how safe and well tolerated the study drug is. Potential participants will be assessed if they are suitable 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. After successfully passing screening into the study, participants will be randomly assigned to receive either DT-101 or placebo for the study. Over the next 8 weeks, these tests and assessments will continue throughout the study with the purpose of checking the participants' ongoing suitability and to collect data to analyse 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.

Inclusion Criteria:

The participant is able to read, understand and communicate in the local language used at the study site, and is willing to provide written informed consent Male or female (assigned at birth, inclusive of all gender identities) participant must be 18 to 75 years of age, inclusive at the time of signing the informed consent.

Has recurrent depression (defined as at least one prior episode excluding the current one), as diagnosed by DSM 5-TR (Diagnostic and Statistical Manual of Mental Disorders, 2022).

Exclusion Criteria:

Pregnant or breastfeeding or plans to become pregnant during the study. Unstable medical condition or unstable chronic disease. Significant neurological abnormality. History of moderate or severe alcohol or drug use disorder as per DSM-5-TR in the 6 months prior to Screening.

History of seizure. In the investigator's opinion, the participant is not capable of adhering to the protocol requirements.