This study is testing a new oral medication called VG081821AC to see if it can help improve movement symptoms in people with early to mid-stage Parkinson's disease. VG081821AC works by blocking a protein in the brain called the adenosine A2A receptor, which may help improve motor function without using levodopa. The main goal is to measure changes in movement symptoms using a standard rating scale called the MDS-UPDRS Part III (Motor Examination). This scale evaluates how well participants can move, walk, and perform daily activities. The study will compare the scores before and after 12 weeks of treatment to see if VG081821AC improves movement symptoms better than the placebo. Currently, levodopa is the most common treatment for Parkinson's disease, but it can cause side effects over time. If VG081821AC works well, it could offer a new treatment option for people in the early to mid-stages of Parkinson's disease who want to delay or avoid starting levodopa. A total of 152 adults (aged 18-80 years) will be enrolled in this trial in China. Participants will be randomly assigned (like flipping a coin) to one of four groups:
* VG081821AC 25 mg (taken twice daily)
* VG081821AC 50 mg (taken twice daily)
* VG081821AC 75 mg (taken twice daily)
* Placebo (a pill with no active drug, taken twice daily)
Participants will visit the study center 8 times to have their movement symptoms, safety, and overall health checked.