This is a phase 1, open-label study to assess the pharmacokinetics, pharmacodynamics, safety, and tolerability of opicapone when administered orally once daily for 14 days as adjunctive therapy to carbidopa/levodopa in subjects with Parkinson's disease.

Inclusion Criteria:

1. Have a clinical diagnosis of idiopathic Parkinson's Disease (PD) for at least 3 years with clear improvement with levodopa treatment
2. Be at a stable dose of maintenance medication(s) for PD, including stable doses of CD/LD
3. Subjects of childbearing potential who do not practice total abstinence must agree to use hormonal or two forms of nonhormonal contraception (dual contraception) consistently during the screening, treatment and follow-up periods of the study
4. Have a body mass index (BMI) of 18 to 40 kg/m2
5. Have a modified Hoehn and Yahr stage of ≤4 in the OFF state
6. Be able to tolerate an overnight period of 12 hours without CD/LD
7. Be in good general health and expected to complete the clinical study as designed

Exclusion Criteria:

1. Are currently pregnant or breastfeeding
2. More than 2 alcoholic beverages daily or more than 14 alcoholic beverages weekly within 7 days of Day -1 or consume any alcohol within 48 hours of Day -1.
3. Have motor fluctuations during the day (ie, effect of levodopa "wearing off" or having unpredictable "off" periods), or severe or intolerable levodopa-induced dyskinesia
4. Have had previous exposure to opicapone, or have an allergy, hypersensitivity, or intolerance to opicapone or other COMT inhibitor.
5. Have a history of a medical condition or surgical procedure that might interfere with absorption or metabolism.
6. Have a known history of neuroleptic malignant syndrome
7. Have an unstable medical condition or chronic disease
8. Have taken certain prohibited medications within 28 days of Day -1.
9. Have a known or suspected diagnosis of AIDS, or have tested seropositive for HIV
10. Have hepatitis A or B
11. Have a significant risk of suicidal or violent behavior