Primary Objective: To compare the efficacy and safety of DVS-233 SR versus placebo treatment in reducing the relapse rate of depressive symptoms in subjects with major depressive disorder (MDD), and to compare the percentages of relapse in terms of time to relapse between DVS-233 SR and placebo treatment groups by using survival analysis.

Secondary Objective: To assess the response of subjects on DVS-233 SR versus placebo for the clinical global evaluation, functionality, general well-being, pain, and absence of symptoms (Hamilton Psychiatric Rating Scale for Depression, 17-item [HAM-D17] < 7).

Inclusion criteria in the open-label phase:

• Outpatients
• Men and women 18 to 75 years of age, inclusive. Sexually active women participating in the study must use a medically acceptable form of contraception (Medically acceptable forms of contraception include oral contraceptives, injectable or implantable methods, intrauterine devices, or properly used barrier contraception)
• Subjects must have a primary diagnosis of MDD based on the criteria in the Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM-IV), single or recurrent episode, without psychotic features (If other allowable psychiatric diagnoses are present, MDD must be the predominant psychiatric disorder present.)

Exclusion Criteria:

• Treatment with DVS-233 SR at any time in the past
• Treatment with venlafaxine (immediate release [IR] or ER) within 90 days of study day 1
• Known hypersensitivity to venlafaxine (IR or ER)