To compare the efficacy of Quetiapine SR versus placebo over 8 weeks in unipolar non-psychotic adult outpatients depression and comorbid fibromyalgia. This will be measured by the last observation carried forward (LOCF) mean change from baseline to week 8 on the Hamilton Depression Scale (HAM-D) total score.

For the purposes of this study, response regarding improvement in depressive symptoms will be defined as a 50% decrease in HAM-D scores over 8 weeks. Furthermore, proportion of patients achieving remission is defined as an HAM-D total score of 7 at end of treatment. The anxiety comorbid symptoms often associated with major depression will be assessed with the HAM-A (14 items) scale. Proportion of patients responding and achieving remission of anxiety symptoms are defined respectively as a reduction of 50% in the HAM-A total score from baseline and a HAM-A total score of 7 at the end of treatment.

Secondary Endpoints include

• Change from baseline to week 8 in Brief Pain Inventory (short form) total score.
• Changes from baseline to week 8 in HAM-A total scores Changes from baseline to week 8 in CGI Severity of illness scores. Clinical Global Impression - Improvement (CGI-I) score from randomisation to Week 8 Change from baseline in the Fibromyalgia Impact Questionnaire (FIQ). Change from baseline in the Sleep Scale from the Medical Outcome Study (MOS). Change from baseline in the Sheehan Disability Scale (SDS). Change from baseline in the Quality of Life Enjoyment and Satisfaction Questionnaire- Short Form (Q-LES-Q-SF).

Change from baseline in the Patient Health Questionaire-15 (PHQ-15). Change from baseline in the Global Assessment Scale (GAS).

The side effects and the tolerability profiles of Quetiapine SR at the dose range used in the study will be assessed at every visit following the initial visit.

Inclusion Criteria:

• Patients with a DSM IV diagnosis of major depression and fibromyalgia confirmed by using the American College of Rheumatology criteria. Male or female between the ages of 18 and 65.
• Patients who score at least 22 on the 17-item HAM-D scale and at least 4 (i.e., moderately ill) on the Clinical Global Impression (CGI) severity scale. Both criteria have to be met at screening and baseline (Study Day 0).

Exclusion Criteria:

• Patients with DSM-IV Axis 1 disorder other than MDD and Chronic Pain Disorder within 6 months of enrolment.
• History of inadequate response to adequate treatment (6 weeks) with 2 or more classes of antidepressants during current depressive episode.
• Patients who, in the investigator's opinion, pose a risk for suicide.
• History of suicide attempt within 3 years of entering study.
• Current depressive episode secondary to general medical condition excluding Fibromyalgia.
• History or presence of bipolar disorder or psychosis.
• Post traumatic stress disorder, anorexia nervosa or bulimia nervosa.
• Patients with diagnosis of DSM-IV Axis II disorder which has a major impact on the patient's current psychiatric status.
• Present DSM IV diagnosis of substance abuse or dependence within 6 months prior of the screening visit (except dependence in full remission, and except caffeine, nicotine or opiate dependence)