A Research Study to Compare the Treatments of a Combination of Elzasonan With Zoloft, to Zoloft Alone, or Placebo in People With Major Depressive Disorder (MDD)

Inclusion Criteria: Adult subjects, 18 years of age or older with a diagnosis of recurrent, moderate-to-severe MDD without psychotic features (DSM-IV 296.3x, with a HAMD17 score >= to 22 and CGI-S >=4. MDD must be the primary psychiatric disorder that motivated the subject to seek treatment and the current episode must be at least 1 month in duration but no longer than 6 months in duration. Exclusion Criteria: Subjects who, in the investigator's judgement, would require treatment with electroconvulsive therapy (ECT), or antipsychotics, or would require a change in intensity of psychotherapy, or subjects who would require treatment with any other psychotherapeutic drugs during the course of the trial. Subjects who have ever been diagnosed with Panic Disorder, Post-Traumatic Stress Disorder, Obsessive-Compulsive Disorder, Bipolar Affective Disorder, Schizophrenia, Schizoaffective Disorder or othe Psychotic Disorder, MDD with a seasonal pattern, or Dissociative Disorders per DSM-IV criteria.