Duloxetine is a selective serotonin and norepinephrine reuptake inhibitor available in delayed-release capsules for oral use. Duloxetine 60 mg/day, compared with placebo, was associated with a greater reduction from baseline in the Brief Pain Inventory (BPI) average pain severity score, a greater improvement in the patient-rated global impression of improvement (PGI-I) scale in patients with fibromyalgia, with or without major depressive disorder, in two 12- and 15-week phase III studies. In a 27-week, phase III trial, there was no significant difference between duloxetine (60 or 120 mg/day) and placebo for the least squares mean change from baseline to endpoint in BPI average pain scores and the PGI-I score. The significant improvements in efficacy that occurred in patients with fibromyalgia during 8 weeks of open-label treatment with duloxetine 60 mg/day were generally maintained during 52 weeks of subsequent blinded treatment at the same dosage in a phase III trial. Nonresponders during treatment with open-label duloxetine 60 mg/day, demonstrated no increased ability to respond if the duloxetine dosage was up-titrated to 120 mg/day than those who remained on the same dosage during the subsequent 52-week, double-blind phase. Duloxetine was generally well tolerated in studies of up to 1 year in duration, with nausea being the most frequent adverse event and main cause for discontinuing therapy.