The primary purpose of this study is to compare the long-term efficacy and safety of desvenlafaxine succinate sustained release versus placebo in adults with Major Depressive Disorder, using a randomized withdrawal design. Randomized withdrawal means that after receiving desvenlafaxine succinate sustained release for a predetermined period of time, subjects will be selected by chance to either continue receiving the study drug or to be withdrawn from the study drug and receive placebo for the remainder of their participation in the trial. Subjects will not know to which group they have been assigned.
The study consists of an up to 14-day screening period followed by an 8-week open-label period in which subjects will knowingly receive 50 mg/day of desvenlafaxine succinate sustained release. Subjects who do not respond to treatment, demonstrating no significant change in their depressive symptoms, will be withdrawn from participation at the end of this period. Responding subjects will receive an additional 3 months of open-label desvenlafaxine succinate sustained release at the same dose. Subjects with stable response to treatment at the conclusion of this 3 month period will be randomized to either desvenlafaxine succinate sustained release at 50 mg/day or placebo in a blinded manner for an additional 6 months or until symptoms of depression return. Following discontinuation at any point after enrollment in the study, subjects will receive two weeks of follow-up monitoring, including one week of blinded taper with 25 mg/day of desvenlafaxine succinate sustained release treatment for any subjects who have been taking desvenlafaxine succinate sustained release prior to discontinuation. Subjects assigned to placebo will receive a blinded placebo taper. Following taper, subjects will be evaluated for one additional week to monitor safety.