Pathogenetic aspects of responsiveness to ondansetron (5-hydroxytryptamine type 3 receptor antagonist) in patients with primary fibromyalgia syndrome--a preliminary study.

Ondansetron appears to be an effective drug in about 50% of patients with FM. There may be 2 subsets of patients with FM that differ clinically and pathogenetically with regard to the disturbance in the 5-HT-3R system.