Study Comparing the Efficacy of Venlafaxine XR Vs. SSRIs and Conventional Antidepressants in Depressed Patients

Main Inclusion Criteria: * Males or females, 18 -65 years of age * Outpatients * Major depressive disorder based on DSM-IV criteria * The baseline score of 17-item HAM-D³17 * Switchers from prior antidepressants, who have had no satisfactory improvement (normally after a minimum of 8weeks of treatment), with an approved antidepressant medication or have experienced intolerance due to side effects to their antidepressant medication based on clinical discretion * Provide written informed consent * If female is of childbearing potential, must be confirmed no pregnancy at baseline, and use a medically acceptable method of contraception throughout the study. Main Exclusion Criteria: * Hypersensitivity to venlafaxine; * Clinically significant renal or hepatic disease or any other medical disease that, in the opinion of the investigator, might compromise the study, including seizure * Alcohol or drug abuse within the last year * A recent history of myocardial infarction or unstable heart disease (within 6 months of baseline) * Bipolar disorder * For female, known or suspected pregnancy or breast feeding * Use of a monoamine oxidase inhibitor (MAOI) within 14 days of baseline; use of any investigational drug within 30 days of baseline. * Patients have prior use of venlafaxine or use of venlafaxine for the current episode.