Background: Alpha-blockers are commonly used to manage lower urinary tract symptoms (LUTS) associated with benign prostatic hyperplasia (BPH), while antimuscarinic agents are prescribed for overactive bladder (OAB). Combining these therapies may improve symptoms, but concerns remain regarding safety in men with bladder outlet obstruction (BOO). Objective: To evaluate the safety of combined solifenacin (SOLI) and tamsulosin oral controlled absorption system (TOCAS) therapy compared with tamsulosin monotherapy in men with LUTS and BOO. Methods: This comparative study included men aged over 45 years with LUTS and BOO for at least three months, total International Prostate Symptom Score (IPSS) ≥ 8, BOO index ≥ 20, maximum urinary flow rate (Qmax) ≤ 12 mL/s, and voided volume ≥ 120 mL. Participants were divided into two groups: one received tamsulosin 0.4 mg alone, and the other received tamsulosin 0.4 mg plus solifenacin 10 mg. Primary safety outcomes were Qmax and detrusor pressure at Qmax (PdetQmax). Secondary assessments included post-void residual volume (PVR), IPSS, and voided volume. Results: At the end of treatment, both groups showed significant improvements in PdetQmax and Qmax. However, the mean increase in PVR was significantly higher in the combination therapy group at all follow-up points, particularly at weeks 2, 12, and end of treatment. Urinary retention occurred in only one patient receiving combination therapy. Study limitations included lack of evaluation of prostate size, high prostate-specific antigen levels, drug cost, and adverse effects. Conclusion: The combination of TOCAS 0.4 mg and solifenacin 10 mg demonstrated efficacy without clinically significant increased risk of urinary retention in men with LUTS and BOO, supporting its safe use in appropriately selected patients.