• Montgomery Asberg Depression Rating Scale (MADRS)
  

• Montgomery Asberg Depression Rating Scale (MADRS)
  
• Hamilton Depression Rating Scale (HAMD)
  
• Hamilton Anxiety Scale (HAM-A)
  
• Clinical Global Impressions (CGI)
  
• Arizona Sexual Experiences Scale (ASEX)
  

Inclusion Criteria:

• Male or female patients 18-65 years of age, inclusive.
• MDD, single or recurrent, according to DSM-IV-TR. Current episode must be less than 1 year but a min. of 4 weeks in duration
• Patients must provide written informed consent prior to beginning any trial related activities.
• Patients must have a HAM-D score >22 on the first 17 items of the 21 item scale at V1 and V2.
• Patients must have a HAM-D, item 1(depressed mood) >2 at V1 and V2.
• Patients must be able to speak, read and understand English and possess the ability to respond to questions and follow simple instructions

Exclusion Criteria:

• Patients who have a current or within 6 months Axis I diagnosis of PTSD, OCD or Eating Disorder. (GAD, Social Phobia and Simple Phobia will be allowed).
• 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 V1 or substance dependence within 6 months prior to V1.
• Patients who meet DSM-IV-TR criteria for MDD Specifiers: with catatonic features; with postpartum onset; or with seasonal pattern.
• Patients who are receiving formal psychotherapy or have had psychotherapy within 12 weeks prior to V1.
• Patients who, in the Investigator’s judgment, pose a serious suicidal or homicidal risk at V1 or V2 or who have made a suicide attempt within 6 months prior to V1.
• 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 V1.
• Patients who are taking psychotropic drugs. Patients who have taken psychotropic drugs must have discontinued these prior to V1. The minimum discontinuation periods prior to V1 are: 4 weeks for MAOIs and fluoxetine; 2 weeks for all other antidepressants, sedatives, hypnotics, beta adrenergic blockers benzodiazepines or other psychoactive medications (including herbals); and 12 weeks for depot neuroleptics.
• Patients taking migraine medications with a serotonergic mechanism of action (e.g., sumatriptan, naritriptan, ergot derivatives).
• Patients with a known hypersensitivity to SSRIs or 5-HT1a agonists.
• Patients previously treated with vilazodone (also known as SB-659746-A or EMD 68843).
• Patients with a history of clinically significant cardiac, renal, neurologic, cerebrovascular, hepatic, hematologic, metabolic or pulmonary disease including: a myocardial infarction within 1 year of V1; diabetes mellitus who require insulin treatment (oral antidiabetic agents OK); history of seizure disorders (except febrile seizures in childhood); prior or current history of neoplastic disease (squamous cell carcinoma of the skin will be allowed); renal impairment (serum creatinine > 1.7mg/dL) or hepatic impairment (ALT or AST three times the upper limit of normal). Patients not euthyroid, unless on thyroid medication; if on thyroid medication must be euthyroid for 6 months before Visit 1.
• Patients with Sicca syndrome.
• Female patients must not be pregnant, not lactating, and not planning to become pregnant during study participation. All female patients who are not at least 1 year post-menopausal or irreversibly surgically sterilized (by hysterectomy, oophorectomy, or bilateral tubal ligation with resection) must have a negative urine pregnancy test at V1 and V2 and must be determined to not be at risk of pregnancy (e.g., abstinent or same-sex partner) and/or must be using adequate and reliable contraception throughout the trial. Adequate contraception is defined as continuous use of one of the following: Norplant (inserted 3 months prior to administration); medroxyprogesterone acetate injection (given >14 days prior to V1); oral contraception (taken as directed for >1 month prior to V1); double-barrier method (e.g., condom and spermicide); IUD (inserted >4 weeks prior to V1); and monogamous partner with a bilateral vasectomy (procedure performed >3 months prior to V1).
• Patients with clinically significant abnormalities on ECG (abnormalities determined by the Investigator and the physician interpreting the ECG) not resolved by V2.
• Patients having clinically significant abnormal laboratory findings at V1 not resolved by V2.
• Patients with a positive drug screen (one re-screen after 4 weeks will be allowed for those testing positive for marijuana).
• Patients who, in the opinion of the Investigator, would be noncompliant with the visit schedule or study procedures (e.g., illiteracy or planned vacations, planned hospitalizations during the study).
• Patients that have taken an investigational drug or participated in an investigational drug trial within the past 30 days.