Study of Lumateperone as Adjunctive Therapy in the Treatment of Patients With Major Depressive Disorder

The study will be conducted in three periods: * Screening Period (up to 2 weeks) during which patient eligibility will be assessed. * Double-blind Treatment Period (6 weeks) in which all patients will be randomized to receive placebo or lumateperone 42 mg/day in 1:1 ratio. * Safety Follow-up Period (1 week) in which all patients will return to the clinic for a safety follow-up visit approximately one week after the last dose of study treatment.