Inclusion Criteria:  diagnosed with PD according to United Kingdom Parkinson's Disease Society Brain Bank (UKPDBB) diagnostic criteria under stable ConM treatment with no alteration of dosage in the past 30 days  Exclusion Criteria:  secondary PD or atypical parkinsonian disorder used antidepressants in the previous month history of psychiatric, mood, or other neurological disorders suicidal (with suicidal thoughts in the past year) history of severe diseases, such as cancer and myocardial infarction participation in another clinical study pregnant or breast-feeding Hoehn and Yahr (H&Y) stage 4 or above deranged liver and renal function