Open-label Trial in Parkinson's Disease (PD)

Rollover participants are eligible for the study if they met the following inclusion criteria: * Participants who complete the 27-week double-blind Treatment Period of Trial CVL-751-PD-001 (NCT04201093) or Trial CVL-751 PD-003 (NCT04542499) or the 27-week double-blind Treatment Period and 10-day Safety/Withdrawal Assessment Period of Trial CVL-751-PD-002 (NCT04223193) and enter this trial within 72 hours after completing the last trial visit in the double-blind trial. Rollover participants from Trial CVL-751-PD-003 must continue to use levodopa/carbidopa (or levodopa/benserazide) for the duration of the trial. * Sexually active men or women of childbearing potential must agree to use acceptable (at minimum) or highly effective birth control, or remain abstinent during the trial and for 4 weeks after the last dose of trial treatment. * Participants who are capable of giving signed informed consent, which includes compliance with the requirements and restrictions listed in the ICF and in the protocol. * Participants who are willing and able to refrain from any PD medications that are not permitted by the protocol (including dopaminergic agents) throughout participation in the trial. * Participant who, in the judgement of the investigator, demonstrated adequate compliance with the IMP and protocol requirements in the double-blind trial.

Rollover participants are excluded from the trial if any of the following met: * Participants who do not enroll in this open-label trial within 72 hours after completing the last trial visit in the double-blind trial * Participants who answer "yes" on the C-SSRS Suicidal Ideation Item 4 or Item 5 (Active Suicidal Ideation with Some Intent to Act, Without Specific Plan, or Active Suicidal Ideation with Specific Plan and Intent) and whose most recent episode meeting the criteria for C-SSRS Item 4 or Item 5 occurred within the last 6 months, OR Participants who answer "yes" on any of the 5 C-SSRS Suicidal Behavior Items (actual attempt, interrupted attempt, aborted attempt, preparatory acts, or behavior) and whose most recent episode meeting the criteria for any of these 5 C-SSRS Suicidal Behavior Items occurred within the last 2 years, OR Participants who, in the opinion of the investigator, present a serious risk of suicide. * Participants who had previously been enrolled in this open-label trial and had subsequently withdrawn.