Background: Use of 5 mg/day finasteride (Proscar) for benign prostatic hyperplasia is known to affect serum concentrations of prostate-specific antigen (PSA). When men taking this treatment undergo screening for prostate cancer, a compensatory adjustment of the PSA concentration (to multiply the value by two) is recommended. Whether this recommendation should apply to men taking 1 mg/day finasteride (Propecia) for the treatment of androgenic alopecia is unknown. We aimed to assess the effect of 1 mg/day finasteride on serum PSA in men aged 40-60 years with male-pattern hair loss. Methods: Between March 13, 1998, and Jan 12, 2000, 355 men aged 40-60 years with male-pattern hair loss were stratified by age decade (40-49 years and 50-60 years), and randomised in a ratio of four to one to 1 mg/day finasteride or placebo. The primary endpoint was the effect of this treatment for 48 weeks on serum PSA concentration compared with placebo. This trial is in the process of being registered on the US National Institutes of Health website http://www.clinicaltrials.gov/ct/show/NCT00396175. Analyses were according to protocol. Findings: Within 48 weeks of randomisation, men aged 40-49 years and 50-60 years who were assigned 1 mg/day finasteride had a median decrease in serum PSA concentration of 40% (95% CI 34-46) and 50% (44-57), respectively. In men assigned placebo, the median changes were 0% [-14 to 14] and a median increase of 13% [2 to 24], respectively. Interpretation: In men aged 40-60 years, 1 mg/day finasteride for 48 weeks lowers serum PSA concentration. Therefore, the existing recommendation for the adjustment of serum PSA concentration in prostate-cancer screening in men taking 5 mg/day finasteride should also apply to men taking the 1 mg/day preparation for male-pattern hair loss. Research is needed to assess the effect of 1 mg/day finasteride preparation beyond 48 weeks of treatment.
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