The study will be conducted in three periods:

• Screening Period (up to 4 weeks) during which patient eligibility will be assessed;
• Double-blind Treatment Period (4 weeks) in which all patients will be randomized to receive placebo or lenrispodun 30 mg/day in 1:1 ratio.
• Safety Follow-up Period (1 week) in which all patients will return to the clinic for a safety follow-up visit approximately one week after the last dose of study treatment.

The MDS-UPDRS evaluates various aspects of Parkinson's disease and has four parts: Part I (Non-motor Aspects of Experiences of Daily Living), Part II (Motor Aspects of Experiences of Daily Living), Part III (Motor Examination), and Part IV (Motor Complications). The MDS-UPDRS evaluates various aspects of Parkinson's disease and has four parts: Part I (Non-motor Aspects of Experiences of Daily Living), Part II (Motor Aspects of Experiences of Daily Living), Part III (Motor Examination), and Part IV (Motor Complications).

Each parkinsonian sign or symptom on the MDS-UPDRS is rated on a 5-point scale (ranging from 0 to 4), with higher scores indicating more severe impairment. The maximum total UPDRS score is 199, indicating the worst possible disability from PD.

Inclusion Criteria:

1. Male or female between 40 and 80 years of age, inclusive
2. Body mass index of 19.0-40.0 kg/m2;
3. Diagnosis of PD that is consistent with the UK Parkinson's Disease Society (UKPDS) Brain Bank diagnostic criteria;
4. Hoehn and Yahr Scale stage classification of 2 or 3 when in the ON state;
5. Have a clinically meaningful response to levodopa (levodopa + DDCI combination) based on Investigator assessment, and meet the following:
   1. Have been on a stable and optimal dose of levodopa (levodopa + DDCI combination: minimum dose of levodopa equivalent to 100 mg three times daily) for at least 4 weeks prior to Screening, and are expected to continue the same dose regimen throughout the Double-blind Treatment Period;
   2. If taking other anti-parkinsonian medications (MAO-B [monoamine oxidase B] inhibitor, COMT [catechol-O-methyltransferase] inhibitor, dopamine agonist) in addition to levodopa, have been on a stable dose for at least 4 weeks prior to Screening and are expected to continue the same dose regimen throughout the Double-blind Treatment Period;

7. Have wearing-off symptoms and levodopa-induced dyskinesia as per Investigator judgment; 8. Properly complete and return a self-reported home diary for motor function status (Hauser Diary) during the Screening Period, which confirms 3 consecutive days (ie, 3 consecutive, 24-hour periods), each with at least 2½ hours of OFF time during waking hours.

9. Has a caregiver to assist with study participation, if determined by the Investigator to be necessary.

Exclusion Criteria:

1. Medical history indicating parkinsonism other than idiopathic PD, including but not limited to, progressive supranuclear gaze palsy, multiple system atrophy, drug-induced parkinsonism, essential tremor, primary dystonia;
2. Has late-stage PD, severe peak-dose dyskinesia, clinically significant end-dose or biphasic dyskinesia, and/or unpredictable or widely swinging fluctuations in their symptoms as assessed by the Investigator;
3. Exhibits clinical signs of dementia as indicated by the Mini-Mental State Examination, 2nd Edition: Standard Version (MMSE-2:SV) score of ≤ 24;
4. Use of moderate or strong CYP3A4 inhibitors within 5 half-lives of Baseline or CYP3A4 inducers within 2 weeks of Baseline;
5. Daily use of nonsteroidal anti-inflammatory drugs (NSAIDs) or acetylsalicylic acid (ASA);
6. Use of MAO-A inhibitors, phosphodiesterase type 5 (PDE5) inhibitors, or alpha blockers including tamsulosin, within 5 half-lives of Baseline;