Randomized, Double-Blind, Placebo Controlled Study of Vilazodone's Efficacy, Safety, and Biomarkers of Response in Major Depressive Disorder (MDD)

Inclusion Criteria:

• Patients 18-70 years of age.

• A diagnosis of MDD, single episode or recurrent, according to DSM-IV-TR (296.2/296.3)with a current Major Depressive Episode of less than two year's duration with aminimum duration of at least 4 weeks.

• Meets DSM-IV-TR criteria for Major Depressive Disorder.

• HAM-D score ≥ 22 on the first 17 items of the 21-item HAM-D.

• HAM-D item 1 (depressed mood) score ≥ 2.

• Patients must be able to provide written informed consent

• Patients must be able to speak, read and understand English

Exclusion Criteria:

• Patients with a current (or within 6 months prior to the Screening Visit) Axis Idisorder of Post Traumatic Stress Disorder, Eating Disorder, Obsessive CompulsiveDisorder.

• Patients with a history of schizophrenia, schizoaffective disorder or bipolar I or IIdisorder (with a history of hypomanic or manic episodes).

• Patients who meet DSM-IV-TR criteria for substance abuse (alcohol or drugs) within 3months prior to the Screening Visit or substance dependence within 6 months prior tothe Screening Visit.

• Patients who meet criteria for any of the following DSM-IV-TR MDD Specifiers: [a] WithCatatonic Features; [b] With Postpartum Onset; [c] With Seasonal Pattern [d]severewith Psychotic Features.

• Patients who are receiving formal psychotherapy or have had psychotherapy within the 12 weeks prior to the Screening Visit.

• Patients who have any one of the following:

• In the month prior to screening, have had active suicidal ideation with someintent to act, without specific plan.

• In the month prior to screening, have had suicidal ideation with specific planand intent.

• Have made a suicide attempt within the 6 months prior to the screening visit.

• In the opinion of the Investigator, is currently at significant risk of suicide.

• Patients who have had an inadequate response to at least 2 consecutive antidepressantsfrom different classes given at adequate doses for an adequate duration.

• Patients who have received electroconvulsive therapy within the 6 months prior to theScreening Visit.

• Patients currently taking a psychotropic drug. Patients who have taken psychotropicdrugs must have discontinued these prior to the Screening Visit. The minimumdiscontinuation periods are outlined in the study protocol.

• Patients taking migraine medications with a serotonergic mechanism of action

• Patients taking CYP3A4 inhibitors such as grapefruit juice, ketoconazole, diltiazem,and macrolide antibiotics or montelukast

• Patients with known hypersensitivity to SSRIs (selective serotonin reyptakeinhibitors) or 5-HT1a agonists.

• Patients previously treated with vilazodone (also known as SB-659746-A or EMD 68 843).

• Patients with a history of clinically significant cardiac, renal, neurologic,cerebrovascular, hepatic, hematologic, metabolic or pulmonary disorders.

• Patients with any serious medical disorder or condition that would, in theinvestigator's opinion, preclude the administration of study medication.

• Female patients must not be pregnant, lactating, or planning to become pregnant duringthe time of study participation. All female patients must be at least 1 year postmenopausal or irreversibly surgically sterilized (by hysterectomy, oophorectomy, orbilateral tubal ligation with resection) or determined not to be at risk of pregnancy.

• Patients with clinically significant abnormalities on electrocardiogram.

• Patients having clinically significant abnormal laboratory findings.

• Patients with a positive drug screen.

• Patients who, in the opinion of the investigator, would be noncompliant with the visitschedule or study procedures.

• Patients that have taken an investigational drug or participated in an investigationaldrug trial within the past 30 days.