The primary objective of the study is to determine whether quetiapine extended-release in combination with cognitive behavioral therapy (CBT) is more effective than CBT plus placebo in treating depressive and anxiety symptoms in patients with both major depression and generalized anxiety disorder. Approximately 64 individuals (adults 18-65) will be randomly assigned to treatment group for 16 weeks. Weekly CBT sessions will be conducted lasting about 45 minutes and weekly visits with the study psychiatrist lasting about 20 minutes in which medication will be discussed. Both clinician administered and self-report measures will be used to compare groups before and after 16 weeks.

This study will evaluate the efficacy of quetiapine extended-release as adjunctive therapy to cognitive behavioral therapy (CBT) compared to CBT plus placebo in the treatment of patients with comorbid major depression and generalized anxiety disorder. We will also evaluate the quality of life in patients with comorbid MDD/GAD, the response and remission rates by treatment group, changes in sleep quality, and tolerability of adjunctive quetiapine to CBT.

Inclusion Criteria:

• Provision of written informed consent
• A diagnosis of both major depression (single episode or recurrent) and generalized anxiety disorder by Diagnostic and Statistical Manual of Mental Disorders- Fourth Edition (DSM-IV)
• Females and/or males aged 18 to 65 years
• Female patients of childbearing potential must be using a reliable method of contraception and have a negative urine human chorionic gonadotropin (HCG) test at enrollment
• Able to understand and comply with the requirements of the study

Exclusion Criteria:

• Pregnancy or lactation
• Any history of psychosis, bipolar disorder, schizophrenia, eating disorders or OCD
• Imminent risk of suicide or a danger to self or others
• Known intolerance or lack of response to quetiapine fumarate, as judged by the investigator
• Use of any of the following cytochrome P450 3A4 inhibitors in the 14 days preceding enrollment including but not limited to: ketoconazole, itraconazole, fluconazole, erythromycin, clarithromycin, troleandomycin, indinavir, nelfinavir, ritonavir, fluvoxamine and saquinavir
• Use of any of the following cytochrome P450 inducers in the 14 days preceding enrollment including but not limited to: phenytoin, carbamazepine, barbiturates, rifampin, St. John's Wort, and glucocorticoids
• Administration of a depot antipsychotic injection within one dosing interval (for the depot) before randomization
• Substance or alcohol dependence at enrollment (except dependence in full remission, and except for caffeine or nicotine dependence), as defined by DSM-IV criteria
• Substance abuse by DSM-IV criteria within 6 months prior to enrollment
• Medical conditions that would affect absorption, distribution, metabolism, or excretion of study treatment
• Unstable or inadequately treated medical illness (e.g. diabetes, angina pectoris, hypertension) as judged by the investigator
• Involvement in the planning and conduct of the study
• Previous enrollment or randomization of treatment in the present study
• Participation in another drug trial within 4 weeks prior to enrollment into this study or longer in accordance with local requirements
• A patient with Diabetes Mellitus (DM)