- Subjects must not require any therapy (including levodopa, dopamine agonists, anticholinergics, amantadine, or selegiline) to treat symptoms of PD at the time of enrollment. Subjects may have had prior exposure to any one of these agents, but exposure with any agent may not have been longer than 60 days in duration and subjects must not have been on any of these agents within 90 days prior to baseline. Once a subject needs dopaminergic treatment, these medications may be added as part of best medical management. The subject will still remain in the study.