A Study to Assess the Efficacy and Safety of REL-1017 as Adjunctive Treatment for Major Depressive Disorder (MDD)

Inclusion Criteria:

• Body mass index (BMI) between 18.0 and 35.0 kg/m2.

• Diagnosed with Major Depressive Disorder (MDD) based on Structured ClinicalInterview for DSM-5 (SCID-5) for MDD.

• Current Major Depressive Episode (MDE).

• Treated on approved, stable first-line anti-depressant therapy with inadequateresponse to 1 to 3 valid courses of treatment with a depressant medication in thecurrent MDE.

Exclusion Criteria:

• Any current and primary psychiatric disorder other than Major Depressive Disorder.

• Severe alcohol or substance use disorder.

• History of bipolar I and II disorder, psychosis, and/or mania.

• Poorly controlled diabetes as defined by HbA1c > 7.5%, despite standard care.Subjects with HbA1c >7.5% may continue in the study if approved by the RelmadaMedical Monitor.

• Having received ketamine or esketamine within 60 days prior to Screening.