Predictors of placebo response in restless legs syndrome studies

Restless legs syndrome (RLS) is a highly prevalent sensorimotor disorder. Effective treatments for RLS have been established in large placebo-controlled trials. These trials have generally employed the International RLS Rating Scale (IRLS) (range 0-40)[1] and Clinical Global Impression of Change (CGI). The interpretation of clinical trials has been mitigated by a large placebo response for both the IRLS and CGI.[2] We wished to evaluate specific patient, scale, and trial design predictors of placebo response.