Inclusion Criteria:

1. Able to understand and willing to voluntarily sign an informed consent form (ICF) and Health Insurance Portability and Accountability Act (HIPAA) authorization or local equivalent if applicable.
2. Diagnosed with idiopathic PD.
3. LD-naïve: defined as subjects not exposed to LD or catechol-O-methyl transferase inhibitors for more than 30 days and the exposure is not within 4 weeks prior to study enrollment.
4. If currently taking anticholinergic therapy, amantadine, or a monoamine oxidase type B (MAO-B) inhibitor, maintains a stable regimen for at least 4 weeks prior to Baseline, and agrees to maintain the stable regimen throughout study participation.
5. Agrees to use a medically acceptable method of contraception throughout the study and for 1 month after completing the study.
6. Able and willing to comply with the protocol, including availability for all scheduled clinic visits and telephone calls.

Exclusion Criteria:

1. Pregnant or breastfeeding.
2. Diagnosed with atypical Parkinsonism or any known secondary parkinsonian syndrome.
3. Prior functional neurosurgical treatment for PD or if such procedures are anticipated during study participation.
4. Use of nonselective MAO inhibitors.
5. Use of dopamine agonists within 30 days prior to Screening.
6. Unable to tolerate a placebo regimen, in the Investigator's opinion.
7. Treatment of psychosis with any antipsychotic.
8. History of seizure or epilepsy.
9. Active or prior medical condition or prior surgical procedure that would interfere with LD absorption.
10. History of narrow-angle glaucoma.
11. Subjects with a history of malignant melanoma.
12. History of myocardial infarction with residual atrial, nodal, or ventricular arrhythmias, upper gastrointestinal hemorrhage, or neuroleptic malignant syndrome.
13. Received any investigational medications during the 30 days prior to Screening.