The purpose of this study is to see the study drug, Mirabegron, is safe and effective in treating symptoms of Overactive Bladder in patients with Parkinson's disease.

This study is a randomized 1:1 placebo-controlled 12-week study of Mirabegron in 144 Parkinson's subjects the age of 40 to 80 with overactive bladder. Active drug will be Mirabegron 50mg daily. Subjects will be enrolled based on response to an overactive bladder questionnaire at visit 1. Enrolled subjects will have 3 study visits to the clinic as well as 1 phone visit.

Inclusion Criteria:

• Subject who signed a consent form approved from IRB(Institutional Review Board) or IEC(Independent Ethics Committee)
• Diagnosis of Parkinson's disease by a neurologist
• taking a Parkinson's medications stably during 4 weeks preceding screening
• 40 Years to 80 Years, Male and Female
• Patient has overactive bladder symptoms more than 4 weeks preceding screening.
• OABSS questionnaires total score≥ 3 and entries of urinary urgency score≥ 2
• The expanded disability status scale ≤ 7

Exclusion Criteria:

• Subjects who have any intervention and operation which can influence on study such as bladder augmentation, vesical sphincter, artificial sphincter, intravesical botulinum toxin treatment etc.
• Use of indwelling catheter or self-catheterization
• acute urinary tract infection or urolithiasis at screening
• History of chronic inflammation such as interstitial cystitis, bladder stones, previous pelvic radiation therapy, or previous or current malignant disease of the pelvic organs
• total volume urine > 3L a day
• Screening post-void residual > 200ml
• Nonpharmacological therapy within the previous 4 weeks of screening
• screening blood pressure >180 systolic or 110 diastolic
• subjects who have orthostatic hypotension, syncope, hypokalemia, or angle-closure glaucoma
• Clinically Significant ECG in recent year
• Screening estimated glomerular filtration rate (eGFR) < 29, AST ( aspartate aminotransferase ) or ALT ( alanine aminotransferase ) > 2x upper limit of normal, γ-GT(gamma-glutamyl transferase) > 3xULN
• take following medication additionally or change the dose: previous 4weeks of screening to end of the study (tamsulosin/silodosin/terazosin, baclofen, diazepam, amitriptyline, DDAVP/desmopressin) previous 12weeks of screening to end of the study (finasteride, dutasteride)
• Use β2- adrenoreceptor agonist, loop diuretic, CYP 3A4 inducer, CYP 2D6 narrow therapeutic index, CYP 3A4 inhibitor, antifungal agent, antiarrhythmic agent
• History of allergy to Mirabegron and beta-adrenergic receptor
• Use of one of the anti-cholinergic bladder medications such as Propiverine / tolterodine / trospium / darifenacin / solifenacin / fesoterodine and mirabegron within 14 days of the screening visit. Subjects who have used one of these medications in the past but discontinued it at least 14 days prior to the screening visit can be enrolled.
• women who have potential to become pregnant during the course of the study