A Study to Evaluate the Efficacy, Safety, and Tolerability of Mirabegron in Men With OAB Symptoms While Taking Tamsulosin Hydrochloride for Lower Urinary Tract Symptoms (LUTS) Due to Benign Prostatic Hyperplasia (BPH)

Inclusion Criteria assessed at Visit 1 (Screening): * Men ≥40 years of age with history of overactive bladder (OAB) symptoms (frequency of ≥8 micturitions per day and urgency episodes of ≥2 per day) while taking tamsulosin hydrochloride for at least 2 months to treat LUTS due to BPH. * Subject has symptoms of OAB (urinary frequency and urgency with or without incontinence) for ≥3 months prior to Screening. * Subject has an International Prostate Symptom Score (IPSS) score ≥8. * Subject has Prostate-Specific Antigen (PSA) \<4 ng/mL or ≥4 but \< 10 ng/mL with a prostate biopsy that is negative for cancer in the past 2 years. * Subject is willing and able to complete the 3-day diary (including urine volumes, vital signs measurements), and Quality of Life questionnaires. * Subject and the subject's spouses/partners who are of childbearing potential must be using a highly effective birth control, which includes established use of oral, injected or implanted hormonal methods of contraception, placement of an intrauterine device (IUD) or intrauterine system (IUS). Birth control must be practiced from Screening and continue throughout the study and for 30 days after the final study drug administration. In addition, sperm donation will not be allowed throughout the study and for 30 days after the final study drug administration. * Subject agrees not to participate in another interventional study while on treatment. Inclusion Criteria assessed at Visit 2 (Baseline) based on the 3-day…