The PLESS Trial: Finasteride for BPH: 4-Year Evidence
Medically reviewed by [Reviewer Name, MD, Urology] | Last reviewed: August 2026 | Editorial policy
The Proscar Long-term Efficacy and Safety Study (PLESS; McConnell et al., 1998; N Engl J Med) was the key 4-year, double-blind, randomized, placebo-controlled trial establishing finasteride 5 mg for BPH. It demonstrated that finasteride significantly reduces the risk of acute urinary retention (AUR) and BPH-related surgery, outcomes that go beyond symptom relief to long-term disease modification.
Study Design
| Parameter | Details |
|---|---|
| Acronym | PLESS (Proscar Long-term Efficacy and Safety Study) |
| Design | Multicenter, double-blind, randomized, placebo-controlled RCT |
| Population | Men with symptomatic BPH and prostate volume ≥40 mL; n=3,040 |
| Treatment | Finasteride 5 mg/day vs. placebo |
| Duration | 4 years |
| Primary endpoints | Time to first occurrence of acute urinary retention or BPH-related surgery |
Key Results
| Outcome | Finasteride 5 mg | Placebo | Relative Risk Reduction |
|---|---|---|---|
| Acute urinary retention | 2.8% | 6.6% | 57% |
| BPH-related surgery | 4.6% | 10.1% | 55% |
| Prostate volume change | −17.9% (55.9 to 45.8 mL) | +14.1% (51.3 to 58.5 mL) | Significant (p<0.001) |
| Maximum urinary flow (Qmax) | +1.9 mL/s | +0.2 mL/s | Net +1.7 mL/s advantage |
| Symptom score improvement (IPSS) | −3.3 points | −1.3 points | 2 points greater reduction |
The PLESS trial established that finasteride is a disease-modifying agent for BPH, not merely a symptomatic treatment. The reduction in AUR and surgery rates is clinically significant, as AUR is a painful, serious complication requiring emergency catheterization. See the full finasteride for BPH guide.
Sources
- McConnell JD, et al. “The effect of finasteride on the risk of acute urinary retention and the need for surgical treatment among men with benign prostatic hyperplasia.” N Engl J Med. 1998;338(9):557-563.