In previous clinical trials in men with androgenetic alopecia, treatment with finasteride increased scalp hair counts in a defined area (i.e. increased hair density).

OBJECTIVES: The current study used a phototrichogram methodology to assess the effect of finasteride on the phases of the hair growth cycle.

PATIENTS/METHODS: Two hundred and twelve men, age 18-40 years, with androgenetic alopecia were randomized to receive finasteride 1 mg daily or placebo for 48 weeks.

At baseline and at 24 and 48 weeks, macrophotographs were taken to measure total and anagen hair count in a 1-cm(2) target area of the scalp.

RESULTS: At baseline, mean total and anagen hair counts in the finasteride group were 200 and 124 hairs, respectively (% anagen = 62%) and the anagen to telogen ratio was 1.74 (geometric mean). In the placebo group, the respective values were 196 and 119 hairs (% anagen = 60%) and 1.57.

At week 48, the finasteride group had a net improvement (mean +/- SE) compared with placebo in total and anagen hair counts of 17.3 +/- 2.5 hairs (8.3% +/- 1.4%) and 27.0 +/- 2.9 hairs (26% +/- 3.1%), respectively (P < 0.001).

Furthermore, treatment with finasteride resulted in a net improvement in the anagen to telogen ratio of 47% (P < 0.001).

In this study, treatment with finasteride 1 mg day(-1) for 48 weeks increased both total and anagen hair counts, and improved the anagen to telogen ratio.

CONCLUSIONS: These data provide direct evidence that finasteride 1 mg daily promotes the conversion of hairs into the anagen phase.

These data support that finasteride treatment results in favourable effects on hair quality that contribute to the visible improvements in hair growth observed in treated patients.