Study design This study is a prospective, single blind trial with a randomized-pairs design comparing L-dopa monotherapy and DAs monotherapy after STN DBS. The trial will be a single-center pilot study, conducted at Toronto Western Hospital, Toronto, Canada. The protocol meets the Ethical Conduct for Research Involving Humans. All patients will provide written informed consent. A total of 40 patients is estimated to be enrolled (20 patients for each treatment group). Duration of the study is 15 months. Enrollment will last for 12 months. The center will enroll patients in pairs, with one patient randomly assigned to L-dopa monotherapy and the other to DAs monotherapy after STN DBS. Randomization will be performed generating a random sequence of number through block randomization. Treatment assignment will be unmasked for the patient but will be blinded for the neurologist programming DBS and evaluating the patient. Another neurologist will be in charge of medication adjustments. Randomization, monitoring, and data management and analysis will be performed at the Toronto Western Hospital.