• Change in the 17 Item Hamilton Rating Scale for Depression (HAM-D-17) score [ Time Frame: Baseline to Study Endpoint ] [ Designated as safety issue: No ]
  

• Response rate (≥ 50% improvement) on HAM-D-17 [ Time Frame: Baseline to Study Endpoint ] [ Designated as safety issue: No ]
  
• Remission rate (≤ 7) on HAM-D-17 [ Time Frame: Baseline to Study Endpoint ] [ Designated as safety issue: No ]
  
• Change in Clinical Global Impressions of Improvement or Severity (CGI-I or S) score [ Time Frame: Baseline to Study Endpoint ] [ Designated as safety issue: No ]
  
• Change in the Quality of Life Enjoyment and Satisfaction Questionnaire (Q-LES-Q) score [ Time Frame: Baseline to Study Endpoint ] [ Designated as safety issue: No ]
  
• Change in Hamilton Rating Scale for Anxiety (HAM-A) [ Time Frame: Baseline to Study Endpoint ] [ Designated as safety issue: No ]
  

120 subjects aged 18 and up with DSM-IV Generalized Anxiety Disorder and Bipolar Disorder type I or II as identified by extensive clinical interview and the Mini-International Neuropsychiatric Interview (MINI) will be enrolled and randomized. Assignment to each arm will be balanced for BP I vs BP II; male vs female; and with vs without SUD. Potential participants will be recruited by means of IRB-approved advertising or from the clinical psychiatric infrastructure.

This study is a randomized, double-blind, placebo-controlled, 8-week comparison of quetiapine SR monotherapy vs. placebo in the acute treatment of comorbid generalized anxiety disorder in patients with bipolar disorder with or without a substance use disorder. Subjects will be assessed weekly for mood changes and side effects.

Inclusion Criteria:

• DSM-IV diagnosis of bipolar I or II disorder, and currently depressed as confirmed by the MINI-Plus at Screening.
• DSM-IV diagnosis of lifetime GAD;
• Hamilton Depression Rating Scale -17 items total score ≥ 18;
• Hamilton Anxiety Rating Scale total score ≥ 18;
• Be male or female at least 18 year old and not older than 65.

Exclusion Criteria:

• Pregnancy or breast feeding.
• Severe medical or neurological problems.
• Severe personality disorder.
• Currently suicidal risk judged by physician.
• Known history of intolerance or hypersensitivity to any of the medications involved in the study.
• Treatment with quetiapine at any dose in the 6 months prior to randomization.
• Known lack of response to quetiapine in a dosage of at least 50 mg for 4 weeks at any time, as judged by the investigator.
• Dependence on opiate, phencyclidine (PCP), and/or barbiturate.
• Acute mania as determined by a score > 12 on the Young Mania Rating Scale at baseline.
• Concurrent OCD.
• Use of any of the following cytochrome P450 3A4 inhibitors in the 14 days preceding enrolment 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 randomisation
• 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 enrolment or randomisation of treatment in the present study.
• Participation in another drug trial within 4 weeks prior enrolment into this study or longer in accordance with local requirements
• A patient with diabetes mellitus (DM) fulfilling one of the following criteria: a. Unstable DM defined as enrollment glycosylated hemoglobin (HbA1c) .8.5% b. Admitted to hospital for treatment of DM or DM related illness within the past 12 weeks c. Not under physician care for DM d. Physician responsible for patient's DM care has not indicated that the patient's DM is controlled f. Physician responsible for patient's DM care has not approved the patient's participation in the study g. 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 h. 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.