The two drug types commonly used to treat symptoms of benign prostatic hyperplasia (BPH), 5α-reductase inhibitors and α 1-blockers, have been shown to have different long-term effects on outcomes such as incidence of acute urinary retention (AUR) and BPH-related surgery. In addition, a comparative study of α 1-blockers and 5α-reductase inhibitors in men with lower urinary tract symptoms showed that the treatment discontinuation rate is higher with α 1-blockers. The risk of treatment failure with α 1-blocker therapy has been shown to be related to baseline prostate volume, with greater failure rates with larger prostate sizes. Clinical data are now available on the dual 5α-reductase inhibitor, dutasteride. Three 2-year phase III randomised, double-blind, placebo-controlled studies have been performed in 4325 men with lower urinary tract symptoms, prostatic enlargement and likely bladder outlet obstruction due to BPH. Compared with placebo, dutasteride significantly improved symptoms from 6 months onwards ( p<0.001). Q max improved significantly in dutasteride-treated patients from 1 month, and dutasteride treatment reduced the risk of AUR by 57% and the risk of BPH-related surgical intervention by 48% compared with placebo. Prostate volume was reduced by a mean of 25.9% and 28.5% at 1 and 2 years, respectively, in dutasteride-treated patients. The most common drug-related adverse events for dutasteride vs. placebo were erectile dysfunction (7% vs. 4%), decreased libido (4% vs. 2%), ejaculation disorders (2% vs. <1%) and gynaecomastia (2% vs. <1%). Adverse events occurred mostly in the first 6 months and their occurrence diminished with time.