A Study in Parkinson's Disease in Patients With Moderate to Severe Dyskinesia

Inclusion Criteria:

• Is able to read, understand, and provide written, dated informed consent prior toScreening Visit.

• Is male or female, between 18 and 80 years of age at Screening Visit.

• Is diagnosed with idiopathic PD that meets UK Parkinson's Disease Society (UKPDS)Brain Bank Clinical Diagnostic Criteria and requires treatment with and showsresponsiveness to levodopa.

• Has experienced dyskinesia over a period of at least 3 months prior to ScreeningVisit

• Has stable peak-effect dyskinesia

• Has more than one hour of "ON" time with troublesome dyskinesia during daily wakinghours on a 24-hour PD subject diary

• Is on a stable levodopa dosing regimen requiring at least 3 dose administrations butno more than 6 dose administrations per day

Exclusion Criteria:

• Has undergone surgery for the treatment of PD

• Has a current diagnosis of Substance Use (including alcohol) Disorder (Abuse orDependence, as defined by Diagnostic and Statistical Manual, Fifth Edition [DSM 5]),

• Has psychiatric diagnosis of acute psychotic disorder or other psychiatric diagnoses

• Has a significant risk for suicidal behaviour in the opinion of the investigatorduring the course of their participation in the study

• Has current seizure disorders (other than febrile seizures in childhood) requiringtreatment with anticonvulsants.

• Has known serious ongoing symptomatic cerebral disease or cerebrovascular disease orany acute brain trauma requiring treatment with anti-convulsant therapy within 5years prior Visit 2, Week 0 (Baseline Visit).

• Has a history of exclusively diphasic, OFF state, myoclonic, dystonic, or akatheticdyskinesia without peak-dose dyskinesia.

Other criteria related to other medical conditions to be referred to the protocol.