This was a multicenter, open-label, long-term study of REL-1017 to evaluate the long-term safety and long-term durability of response in patients with MDD. Patients who completed previous randomized, double-blind Phase 3 trials (NCT04688164, NCT04855747, NCT05081167) of REL-1017 as adjunctive therapy or monotherapy for MDD were asked to continue treatment with REL-1017 25 mg daily for up to 1 year. De novo patients who satisfied inclusion/exclusion criteria also were enrolled and received a 75 mg loading dose of REL-1017 on Day 1 followed by a maintenance dose of 25 mg REL-1017 daily for the remainder of the study (Days 2-365). When REL-1017 was administered as adjunctive treatment, patients continued to use a stable dosage of their concomitant antidepressants.