The purpose of this study is to determine whether RX-10100 are effective in the treatment of Major Depressive Disorder (MDD).

Inclusion Criteria:

• Moderate to severe MDD as determined by the DSM-IV-TR Axis 1 Disorders and by the Montgomery Asberg Depression Rating Scale (MADRS).

Exclusion Criteria:

• Women who are pregnant, women who will be breastfeeding during the study, and women with childbearing potential who are not willing to practice a reliable method of birth control
• Depressive episode duration of less than 1 month
• Lifetime history of any psychotic disorders
• Anxiety disorders
• Significant suicidality
• Clinically significant medical conditions