Study is a multicenter, randomized, double-blind, parallel, placebo-controlled, 20-week trial with 4 study periods. Participants who screen successfully (Study Period I) will be randomized in a 1:1 fashion to duloxetine 60 mg QD or placebo. Starting with Study Period II, participants will be treated in a double-blind manner for 6 weeks. Participants who complete the 6-week, double-blind period will have the opportunity to participate in a 12-week, open-label, flexible-dose portion of the study (Study Period III). Study Period IV is a taper phase designed to reduce the occurrence of discontinuation adverse events. Participants may enter Study Period IV at any time after Visit 3.