Quetiapine Extended Release (XR) Treatment of Major Depressive Disorder With Comorbid Generalized Anxiety Disorder

Inclusion Criteria: * Able to provide informed consent before beginning any study-specific procedures * Male and female patients at least 18 years of age - 70 years of age * Meets Diagnostic and Statistical Manual IV (DSM-IV) criteria for MDD, currently depressed * DSM-IV diagnosis of current GAD * Women with reproductive potential must have a negative urine pregnancy test Exclusion Criteria: * Patients who have had a current episode of depression for less than 4 weeks from enrollment * Patients who have been treated for their current depressive episode for more than 3 weeks with Quetiapine therapy 50 mg/day * Patients currently taking antidepressants known to cause somnolence/sedation such as mirtazapine or unable to wean off current antidepressant if they choose monotherapy * Patients who meet DSM-IV criteria for substance dependence confirmed by the Substance Use Disorder Module of the Structured Clinical Interview for DSM-IV (SCID), for any substance except for caffeine and nicotine, with substance abuse within last 3 months or substance dependence within last 6 months; * Concurrent obsessive-compulsive disorder * Patients with a history of clinically significant cardiac, renal, neurologic, cerebrovascular, metabolic, or pulmonary disease, or other disease or clinical finding that is unstable or that, in the opinion of the investigator, would be negatively effected by trial medication or that would effect trial medication * A patient with diabetes mellitus (DM) fulfilling one of the following criteria: * Unstable DM defined as enrollment glycosylated hemoglobin (HbA1c) \> 8.5% * Admitted to hospital for treatment of DM or DM related illness within the past 12 weeks * Not under physician care for DM * Physician responsible for patient's DM care has not indicated that the patient's DM is controlled * Physician responsible for patient's DM care has not approved the patient's participation in the study * Has not been on the same dose of oral hypoglycemic drug(s) and/or diet for the 4 weeks before randomization (for thiazolidinediones (glitazones) this period should not be less than 8 weeks before randomization) * Taking insulin whose daily dose on one occasion in the past 4 weeks has been more than 10% above or below their mean dose in the preceding 4 weeks Note: If a patient with DM meets one of these criteria, the patient is to be excluded even if the treating physician believes that the patient is stable and can participate in the study. A patient could be enrolled at a later time if DM is stabilized.