OBJECTIVES: To evaluate the efficacy and safety of duloxetine 30 mg/d in adults with fibromyalgia. METHODS: This 12-week, randomized, double-blind, placebo-controlled study was conducted in the United States, Mexico, Argentina, and Israel and enrolled patients meeting the criteria for primary fibromyalgia as defined by the American College of Rheumatology. The primary endpoint was the average pain severity item from the Brief Pain Inventory (BPI)-Modified Short Form, assessed by an analysis of covariance model using change from baseline to the modified baseline-observation-carried-forward endpoint. Secondary endpoints included the Patient Global Impression of Improvement (PGI-I) score and the Fibromyalgia Impact Questionnaire (FIQ) total score and those measuring pain, depression, anxiety, health outcomes, and safety. RESULTS: Patients (mean age, 51 y; 95% female; 87% White; 22% with major depressive disorder) received duloxetine 30 mg/d (N=155) or placebo (N=153). Duloxetine-treated patients did not have a statistically significant BPI-Modified Short Form average pain severity reduction versus placebo-treated patients (-2.04 vs. -1.70; P=0.202). There was a significant difference between duloxetine-treated and placebo-treated patients (P<0.05) for the PGI-I endpoint score (2.97 vs. 3.35) and the changes in FIQ total score (-14.62 vs. -9.75) and the Short-Form Health Survey (SF)-36 mental component score. Discontinuations due to adverse events did not differ significantly between treatment groups; nausea and dry mouth were the only adverse events with a significantly higher incidence with duloxetine versus placebo. DISCUSSION: Duloxetine 30 mg/d did not significantly reduce pain severity in patients with fibromyalgia. However, duloxetine-treated patients reported global improvement in symptoms and function. Safety findings were consistent with the known duloxetine safety profile.