Phase 2 Study of NV-5138 in Adults With Treatment Resistant Depression

Inclusion Criteria: * Male or female, aged 18 to 70 years at Screening. * Diagnosis of Major Depressive Disorder (MDD) according to the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5) for either recurrent or single episode MDD without psychotic features that is confirmed by the Mini International Neuropsychiatric Interview (MINI). * Montgomery-Asberg Depression Rating Scale (MADRS) Total Score of ≥24 for the current MDE at all Screening visits and Baseline (Day 1). * CGI-S score of ≥4 (moderately ill or worse) at the Screening visits and Baseline. * History of inadequate response to ≥1 but ≤4 prior ADT therapies (including the current ADT for the current MDE) ≥ 2 weeks at Screening and ≥ 8 weeks at Baseline. * Stable therapeutic dose of one of the following ADTs for the current MDE for ≥2 weeks prior to Screening and maintain the therapeutic dose throughout the study: citalopram, escitalopram, paroxetine, fluoxetine, sertraline, duloxetine, venlafaxine (IR or XR), desvenlafaxine, vilazodone, levomilnacipran, vortioxetine, bupropion or dextromethorphan//bupropion. * Detectable blood level of the approved ADT at Visits 1 and 2 of the Screening Period. Exclusion Criteria: * MADRS Total Score improvement of ≥25% from the highest to the lowest score during the Screening Period and Baseline. * Clinically significant abnormal laboratory profiles, vital signs, or electrocardiograms (ECGs), per Investigator judgment. * Judged by the Investigator to be at …