A phase III randomized , placebo-controlled , double-blind clinical trial at 67 North American sites consisting of participants 30 years of age or older who received a diagnosis of PD within 5 years and who had the following inclusion criteria : the presence of a rest tremor , bradykinesia , and rigidity ; a modified Hoehn and Yahr stage of 2.5 or less ; and no anticipated need for dopaminergic therapy within 3 months .