To evaluate the efficacy and safety of AXS-05 relative to bupropion in subjects with treatment resistant major depressive disorder (MDD).

This is a randomized, double-blind, active-controlled, 12-week, two-period study consisting of an open-label, bupropion lead-in period, and a double-blind treatment period. The trial is being conducted in subjects with treatment resistant MDD.

Subjects will be considered to have treatment resistant MDD if they have had a historical inadequate response to 1 or 2 antidepressant treatments and a prospective inadequate response to treatment with bupropion during the open-label, lead-in period.

Key Inclusion Criteria:

• Currently meets DSM-V criteria for MDD
• History of inadequate response to 1 or 2 adequate antidepressant treatments
• Body mass index (BMI) between 18 and 40 kg/m2, inclusive
• Agree to use adequate method of contraception for the duration of the study
• Additional criteria may apply

Key Exclusion Criteria:

• Suicide risk
• Treatment with any investigational drug within 6 months
• History of electroconvulsive therapy (ECT), vagus nerve stimulation, transcranial magnetic stimulation, or any experimental central nervous system treatment during the current episode or in the past 6 months
• Pregnant, breastfeeding, or planning to become pregnant or breastfeed during the study
• Additional criteria may apply