Information and Solutions for Men and Women

How 5-Alpha-Reductase Inhibitors Work and Evidence of Benefit

Clinical studies show finasteride may help regrow hair and increase hair density in some men with male pattern hair loss.

Both common male balding and female pattern hair loss are intricately linked to androgen hormones, with the effects of the androgens testosterone and its more potent metabolite DHT more directly seen in men.2, 22 Multiple studies confirm that drugs that inhibit 5α-reductase significantly block the amount of enzyme available to metabolize DHT out of testosterone, which can directly affect hair loss related to these androgen hormones.22 This is because scientific evidence points to the conversion of the hormone testosterone to 5α-dihydrotestosterone (DHT) as having a greater role in androgenetic hair loss than testosterone levels by themselves. The enzyme 5α-reductase is necessary for this conversion, with the type 2 form particularly active in scalp hair follicles.3

In men, finasteride inhibits the type-2 version of 5α-reductase and reduces DHT levels by up to 70%, while dutasteride reduces by both types of the enzyme with even more potent suppression of DHT.3 In men with common balding, orally administered 5α-reductase enzyme inhibitors such as finasteride and dutasteride have been shown to effectively increase hair counts and densities by blocking the production of DHT.22

Clinical Studies Show 5α-Reductase Inhibitors Effectively Treat Thinning Hair

Both finasteride and dutasteride, 5α-reductase inhibitors have been extensively studied in men with male pattern hair loss with positive evidence of their effectiveness in treating male balding.22 Fewer studies have been conducted involving women with androgenic hair loss, and the clinical results have been mixed. However, generally speaking both drugs have been shown to work for some women with female or male pattern hair loss.30 In one study, when combined with 5% topical minoxidil, 5 mg/day of finasteride significantly reduced DHT levels and hair loss in over 90% of women treated.30

Evidence of Success in Male Balding

In placebo-controlled, long term clinical trials with balding men, daily doses of 1-mg finasteride stopped the progression of balding and regrew some hair in over 65% of the men. Typically the maximum rate of improvement (an average of 10% increase in number of terminal hairs) is seen after about 12 months of use and slows down after 24 months. However, finasteride’s benefits are still seen after 60 months of use when compared to placebo. The finasteride-treated group generally maintained the increased hair counts seen at the end of the first year, while the placebo group showed an average 30% decrease in total hair count. A subset of men was switched from finasteride to placebo or vice-versa at the end of the first year. Those who had been on placebo showing increased hair counts in the second year during finasteride treatment. Meanwhile the group originally treated with the drug in the first year had decreased hair counts by the end of the second year of placebo treatment.22

The same studies demonstrated that finasteride also increases hair density in men. After two years of treatment, 66% of patients had higher hair densities, compared to only 7% of those in the group given a placebo. Five years of treatment showed that 48% of finasteride-treated men in these clinical trials still had moderately to greatly-improved hair regrowth, 10% worsened, and 42% were unchanged. Conversely 75% of men in the untreated placebo group had worse hair loss after five years, with 25% unchanged.22

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Women with excessive levels of androgens can show the same areas of hair loss in men with androgenic alopecia.