The phase 1 trials of finasteride (Propecia/Proscar; Merck) have shown that finasteride at 1 mg (Propecia) as well as finasteride at 5 mg (Proscar)blocks 5-α reductase.
The genetic, biochemical, epidemiological, experimental, and clinical reasons for my warning1,2 3years ago that use of finasteride promotes prostate cancer have been confirmed by the findings of a finasteride chemoprevention trial (Prostate Cancer PreventionTrial [PCPT]) involving 18 882 men followed up for 7 years. The trial was stopped after 9060 men underwent biopsy during the trial or at the endof 7 years.
Pitts, Jr WR. Finasteride (Propecia) and the Promotion of High-grade Prostate Cancer. Arch Dermatol. 2004;140(7):885-886. doi:10.1001/archderm.140.7.885-b