The objective of this study is to evaluate the effects of selective alpha-2 adrenergic receptor antagonism on the severity of parkinsonian signs and dopaminomimetic drug-associated motor response complications in patients with mild to moderately advanced Parkinson's disease. In a controlled proof-of-principle clinical study, the acute efficacy of JP-1730 will be assessed through the use of validated motor function scales. Safety will be monitored by means of frequent clinical evaluations and laboratory tests.