This randomized, double-blind, placebo-controlled, multicenter, 8-week, clinical trial is designed to assess the efficacy and safety of vilazodone and to evaluate genetic biomarkers of treatment response associated with vilazodone use in adult patients diagnosed with MDD by the DSM-IV-TR criteria.

This randomized, double-blind, placebo-controlled, multicenter, 8-week, clinical trial is designed to assess the efficacy and safety of vilazodone and to evaluate genetic biomarkers of treatment response associated with vilazodone use in adult patients diagnosed with MDD by the DSM-IV-TR criteria. This study will enroll approximately 470 patients at approximately 10 clinical sites. Safety and efficacy will be assessed at each visit. A DNA sample will be collected and analyzed for response to vilazodone.

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 a minimum 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 I disorder of Post Traumatic Stress Disorder, Eating Disorder, Obsessive Compulsive Disorder.

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

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

• Patients who meet criteria for any of the following DSM-IV-TR MDD Specifiers: [a] With Catatonic Features; [b] With Postpartum Onset; [c] With Seasonal Pattern [d]severe with 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 some intent to act, without specific plan.
  • In the month prior to screening, have had suicidal ideation with specific plan and 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 antidepressants from different classes given at adequate doses for an adequate duration.

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

• Patients currently taking a psychotropic drug. Patients who have taken psychotropic drugs must have discontinued these prior to the Screening Visit. The minimum discontinuation 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 reyptake inhibitors) 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 the investigator's opinion, preclude the administration of study medication.

• Female patients must not be pregnant, lactating, or planning to become pregnant during the time of study participation. All female patients must be at least 1 year post menopausal or irreversibly surgically sterilized (by hysterectomy, oophorectomy, or bilateral 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 visit schedule or study procedures.

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