6-week Study Treatment to Evaluate the Safety and Effectiveness of AZD2066 in Patients With Major Depressive Disorder

Inclusion Criteria: * Provision of signed, written, and dated Informed Consent * Documented primary clinical diagnosis of Major Depressive Disorder Exclusion Criteria: * Patients with a secondary psychiatric disorder including bipolar disorder, psychotic disorders (i.e. schizophrenia, schizoaffective disorder, depression with psychotic features), GAD and social anxiety disorder * Patients whose current episode of depression started less than 4 weeks before enrollment * History of inadequate response of antidepressants during current depressive episode