After a 4-week placebo lead-in period , men aged 45 years with an International Prostate Symptom Score ( IPSS ) of 13 and a maximum urinary flow rate of 4 to 15mL/s received placebo ( 172 men ) , tadalafil 5mg ( 171 ) , or tamsulosin 0.4 mg ( 168 ) once daily for 12 weeks .