A Study for Adolescents With Fibromyalgia Syndrome

Inclusion Criteria: * Meet criteria for juvenile primary fibromyalgia syndrome as defined by Yunus and Masi. * Have a score of greater than or equal to 40mm on item 3 of the Pediatric Pain Questionnaire at screening and treatment baseline. * Female patients must have a negative pregnancy test at baseline and must agree to abstain from sexual activity or use a reliable method of birth control. * Patients must be capable of swallowing study drug whole. * Patients must have venous access sufficient to allow blood sampling and be compliant with blood draws as per the protocol. Exclusion Criteria: * Are currently enrolled in, or discontinued within the last 30 days from, a clinical trial involving an investigational drug or device, or off-label use of a drug or device, or are concurrently enrolled in any other type of medical research judged not to be scientifically or medically compatible with this study. * Have pain symptoms related to traumatic injury, past surgery, structural bone or joint disease (such as osteoarthritis, bursitis, tendonitis), or regional pain syndrome that will interfere with the interpretation of outcome measures. * Have a confirmed current or previous diagnosis of rheumatoid arthritis, inflammatory arthritis, or infectious arthritis, or an autoimmune disease. * Have any primary Axis diagnosis OTHER than major depressive disorder (MDD) and/or generalized disorder (GAD) as defined by the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV), currently or within the past year. Patients with specific phobias may participate in this study. * Have any lifetime DSM-IV Axis I diagnosis of psychosis, bipolar disorder, or schizoaffective disorder. * Have any DSM-IV Axis II disorder which, in the judgment of the investigator, would interfere with protocol compliance. * Have a history of substance abuse or dependence within the past year, excluding nicotine and caffeine. * Have a positive urine drug screen for any substances of abuse or excluded medication. * Have a family history of 1 or more first-degree relatives (parents or siblings) with diagnosed bipolar I disorder. * Have a significant suicide attempt within 1 year of screening or are currently at suicidal risk in the opinion of the investigator. * Have a weight less than 20 kg at any screening phase. * Have initiated, stopped, or changed the type or intensity of psychotherapy within 3 months prior to screening. * Have a history of seizure disorder (other than febrile seizures). * Have abnormal thyroid-stimulating hormone (TSH) concentrations. Patients with hypothyroidism who have been treated on a stable dose of thyroid supplement for at least the past 3 months and have medically appropriate TSH concentrations, and are clinically euthyroid may participate in the study. * Have acute liver injury or sever cirrhosis. * Have previously taken duloxetine. * Have a serious or unstable medical illness. * Have initiated or discontinued hormone therapy within the previous 3 months.