Inclusion Criteria:

• willing and able to give informed consent
• age 30 years or older at time of diagnosis of Parkinson’s disease

• have idiopathic Parkinson’s disease, defined as:

  • having at least 2 of the following 4 signs: resting tremor, bradykinesia, rigidity, or postural reflex impairment, at least one of which must be resting tremor or bradykinesia
  • no secondary or atypical parkinsonism
  • asymmetric features (current signs or history of asymmetric onset)
  • response to L-dopa, by patient self-report
• Parkinson’s disease duration of no more than 5 years
• receiving stable therapy of L-dopa/DCI for at least 3 months; acceptable dose range: 250 mg – 1000 mg L-dopa/DCI daily
• Hoehn and Yahr stage < 4 on stable L-dopa/DCI treatment

Exclusion Criteria:

• have atypical parkinsonism due to drugs, metabolic disorders, encephalitis, or other neurodegenerative diseases
• have any other known medical or psychiatric condition that may compromise their participation in the study
• have taken another investigational drug within 90 days of baseline
• have a change in dosage of any other antiparkinsonian drug (eg, pramipexole, ropinirole, pergolide, bromocriptine, methylphenidate, anticholinergics, or amantadine) during the study or within 90 days prior to baseline
• have received treatment with dopamine blocking agents (including neuroleptic agents, antiemetic agents), dopamine-depleting agents (including reserpine or tetrabenazine) within 90 days prior to baseline
• do not consent to participate