The goal of this clinical trial is to learn if this study drug, ENERGI-F705 Tablets, is safe and works to treat participants who have Parkinson's disease and are currently on standard-of-care antiparkinsonian medications. The main question it aims to answer is:

Does ENERGI-F705 Tablets work to treat Parkinson's disease when used with standard-of-care treatment?

Investigators will compare the three treatment groups, high-dose ENERGI-F705 Tablets (120 milligrams twice daily), low-dose ENERGI-F705 Tablets (60 milligrams twice daily), and placebo tablets (a look-alike substance that contains no drug), to see if ENERGI-F705 Tablets work to treat Parkinson's disease.

Participants will:

• Take the study drugs twice a day for 72 weeks in the treatment group
• Take routine use of standard-of-care antiparkinsonian medications throughout the study
• Visit the outpatient department at scheduled visits, ranging from Day 1 to approximately every 1 to 4 weeks thereafter, for checkups and tests

Inclusion Criteria:

A subject is eligible for the study if all of the following apply:

1. With either gender aged ≥ 40 to ≤ 75 years old at Visit 1 (Screening Visit)

2. Has been diagnosed with idiopathic Parkinson's disease (defined by the Movement Disorder Society (MDS) Clinical Diagnostic Criteria for Parkinson's disease) for ≥ 2 years prior to or at Visit 2 (Day 1)

3. Has a modified Hoehn and Yahr stage of 2 to 3 while assessed in the medication-off state at Visit 1 (Screening Visit)

4. With MDS-UPDRS Part III (motor examination) score of 15 to 60 while assessed in the medication-off state at Visit 1 (Screening Visit)

5. Without motor complications, which is defined as a score of 2 or less on the MDS-UPDRS Part IV score at Visit 1 (Screening Visit)

6. Has received a stable standard-of-care regimen, as determined by the investigator, during the 12 weeks prior to Visit 2 (Day 1) and is currently on the following antiparkinsonian medications with an average levodopa equivalent daily dose (LEDD) of ≥ 300 mg during the same period, including:

   • Levodopa
   • Catechol-O-methyl transferase (COMT) inhibitors
   • Monoamine Oxidase-B (MAO-B) inhibitors
   • Ergot-derived dopamine receptor agonists
   • Non ergot-derived dopamine receptor agonists
   • Others with established levodopa-conversion factors

7. Has adequate indices as follows at Visit 1 (Screening Visit):

   • Hematology: white blood cells (WBC) should be ≥ 3,000 cells/μL, platelet count should be ≥ 80,000 per μL of blood
   • Coagulation: prothrombin time, international normalized ratio (INR), and activated partial thromboplastin time (APTT), all of which should be ≤ 1.5 times the upper limit of the normal range (ULN)
   • Liver function: serum total bilirubin should be ≤ 1.5 times ULN, and aspartate aminotransferase (AST) and alanine aminotransferase (ALT) should be ≤ 3 times ULN
   • Renal function: an estimated glomerular filtration rate (eGFR) should be ≥ 60 mL/min/1.73m2, calculated by the 2021 Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) creatinine equation

8. Is willing and able to comply with all required study visits and follow-ups required by this protocol

9. Understands the study procedures and provided written informed consent (including through use of a legally authorized representative, if necessary)

10. Is able to complete all subject-reported outcome measures

Exclusion Criteria:

Any subject meeting any of the exclusion criteria will be excluded from study participation:

1. Has been diagnosed with atypical Parkinson's disease or secondary parkinsonism

2. Has any of the following neurosurgical intervention for Parkinson's disease within 2 years prior to or at Visit 2 (Day 1):

   • Deep brain stimulation
   • Pallidotomy
   • Thalamotomy
   • Other procedures that may affect motor function

3. With Mini-Mental State Examination (MMSE) score of < 24 at Visit 1 (Screening Visit)

4. With a lifetime history of significant psychiatric disorder (e.g., alcohol use disorder, drug abuse, or suicide attempt), which in the investigator's opinion, may interfere with study participation

5. With history of malignancy or current malignancy within 2 years prior to or at Visit 2 (Day 1)

6. With ongoing or a documented history of within 2 years prior to or at Visit 2 (Day 1) of acute diseases or severe medical conditions, including:

   • Cardiovascular (myocardial infarction, congestive heart failure, New York Heart Association Grade III or IV)
   • Pulmonary (severe chronic obstructive pulmonary disease, pulmonary hypertension, or other clinically significant respiratory conditions)
   • Current severe infections, medical history, physical examination findings, or laboratory examination abnormality that in the investigators' opinion are not in stable condition and participating in the study could interfere with the results of the trial or adversely affect the safety of the subject

7. Administered dopamine-blocking agents within 12 weeks prior to or at Visit 2 (Day 1), including:

   • Typical antipsychotics (e.g., Haloperidol, Chlorpromazine)
   • Atypical antipsychotics (e.g., Risperidone, Quetiapine or Clozapine)

8. With clinically significant gastrointestinal disorders that may affect oral drug absorption or tolerability (e.g., inflammatory bowel disease within 12 weeks prior to or at Visit 2 (Day 1) or relevant gastrointestinal surgery recorded on a lifetime basis)

9. With a history of gout or urolithiasis, or treatment with medications for gout or urolithiasis, within 2 years prior to or at Visit 2 (Day 1)

10. With known hypersensitivity to any component of the investigational product

11. Has participated in another clinical trial involving an investigational product, medical device, or surgical procedure within 4 weeks prior to Visit 1 (Screening Visit)

    * Note: Subjects enrolled in non-interventional clinical trials will be eligible.

12. Female subject with childbearing potential who is lactating or has positive serum or urine pregnancy test at Visit 2 (Day 1)

    * Note: Female subjects with any of following conditions are considered not with childbearing potential

    • With menopause ≥ 1 year
    • Prior surgical procedures resulting in infertility
    • Documented follicle-stimulating hormone or luteinizing hormone levels consistent with postmenopausal status

13. Female subjects with childbearing potential or male subjects with partners of childbearing potential who refuse to use highly effective contraceptives from signing informed consent until the end of study (EOS) or early termination (ET) visit

    * Note: At least two forms of birth control must be adopted and one of which must be a barrier method. Acceptable forms include:

    • Established use of oral, injected or implanted hormonal methods of contraception
    • Placement of an intrauterine device (IUD) or intrauterine system (IUS)
    • Barrier methods of contraception: condom, or occlusive cap (diaphragm or cervical/vault caps)

14. Is an employee of the investigator's site, the sponsor, or its delegate (e.g., contract research organization) who is directly involved in the conduct of the study