In this trial, participants will be randomly assigned to receive either fluoxetine or placebo. Treatment will consists of two phases (acute treatment and maintenance). In the acute treatment phase, participants will receive fluoxetine or placebo daily for 12 weeks. Participants will be followed every 2 weeks. In the Maintenance phase, participants showing significant improvement after 12 weeks may continue treatment for an additional 6 months. In this phase, participants are followed every 4 weeks.