A Study of Tadalafil (LY450190) in Participants With Lower Urinary Tract Symptoms (LUTS) Suggestive of Benign Prostatic Hyperplasia LUTS (BPH-LUTS).

Inclusion Criteria: * Present with benign prostatic hyperplasia (BPH; also referred to as BPH-LUTS), based on the disease diagnostic criteria, at study entry. * Have been treated with a stable dose of an alpha1 blocker (tamsulosin 0.2 mg once daily or silodosin 4 mg twice daily) for at least 8 weeks prior to screening, and continue the same alpha1 blocker at the same dose for the entire duration of the study. * Are Japanese men. * Have prostate volume ≥20 milliliters (mL) estimated by transabdominal or transrectal ultrasound at screening. * Have BPH-LUTS with a Total International Prostate Symptom Score (IPSS) of ≥12 at screening and baseline. * Have moderate LUTS with urinary peak flow rate (Qmax) ≥4 to ≤15 mL/second at baseline, while meeting both of the following criteria: * Prevoid total bladder volume ≥150 to ≤550 mL as assessed by ultrasound * Minimum voided volume ≥125 mL * Demonstrate ≥80% compliance with alpha1 blocker treatment\* during the screening period, documented at baseline * \*Tamsulosin: (Number of doses taken / Number of days to be treated) × 100 * Silodosin: (Number of doses taken / Number of days to be treated) × 50 Exclusion Criteria: * Prostate-specific antigen (PSA) \>10.0 nanograms (ng)/mL at screening. * PSA ≥4.0 to ≤10.0 ng/mL at screening if prostate malignancy has not been ruled out to the satisfaction of a urologist. * Bladder post-void residual (PVR) ≥150 mL by ultrasound determination at screening. * History of any of the following pelvic conditions: * Pelvic surgery or any other pelvic procedure, including radical prostatectomy, pelvic surgery for removal of malignancy, or bowel resection * Pelvic radiotherapy * Any pelvic surgical procedure on the urinary tract, including minimally invasive BPH-LUTS therapies and penile implant surgery * Lower urinary tract malignancy or trauma * Lower urinary tract instrumentation (including prostate biopsy) within 30 days of screening. * History of urinary retention or lower urinary tract (bladder) stones within 6 months of screening. * History of urethral obstruction due to stricture, valves, sclerosis, or tumor at screening. * History of any of the following treatments within the indicated duration: * Antiandrogens within 11 months before screening * Dutasteride within 5 months before screening * Finasteride within 2 months before screening * Any erectile dysfunction treatment previously or currently * Any overactive bladder treatment within 4 weeks before screening * Have a diagnosis or history of prostate cancer at screening. * Current or history of malignancy at screening (except for treatment-free and relapse-free for ≥3 years at screening). * Clinical evidence or history of any of the following bladder conditions: * Underactive Bladder * Detrusor-sphincter dyssynergia (contraction of the detrusor without sphincter relaxation) * Interstitial cystitis * Clinical evidence of any of the following urinary tract conditions: * Active urogenital infection * Clinically significant microscopic hematuria as determined by a urologist * History of significant renal insufficiency meeting either of the following: * Receiving renal dialysis * Creatinine clearance (CLcr) \<30 mL/minute * Clinical evidence of severe hepatic impairment or Aspartate Transaminase (AST) or Alanine Transaminase (ALT) \>3 times the upper limit of normal range. * History of any of the following cardiac conditions: * Current or history of angina requiring treatment with nitrates or nitric oxide donors * Current or history of unstable angina * Positive cardiac stress test without documented evidence of subsequent, effective cardiac intervention (e.g., coronary angioplasty) * History of any of the following coronary conditions within 90 days of screening: * Myocardial infarction * Coronary artery bypass graft surgery * Percutaneous coronary intervention (for example, angioplasty or stent placement) * Any evidence or history of heart failure (New York Heart Association \[NYHA\] ≥ Class III). * Currently receiving alpha1 blocker therapy for the treatment of hypertension. * Current or history of any of the following symptoms: * Symptoms associated with orthostasis (e.g., recurrent episodes of dizziness, lightheadedness, loss of consciousness, syncope) * Causeless fall within 1 year of screening * Blood pressure-related findings of any of the following at screening: * Systolic blood pressure \>160 or \<90 millimeters of mercury (mm Hg) * Diastolic blood pressure \>100 or \<50 mm Hg * Malignant hypertension * Uncontrolled arrhythmia