How 5-Alpha-Reductase Inhibitors Work and Evidence of Benefit
Both common male balding and female pattern hair loss are intricately linked to androgen hormones. However, the effects of the androgen hormones testosterone and its more potent metabolite DHT are more directly seen in men.(2, 22)
The Importance of DHT
The conversion of the hormone testosterone to DHT plays a greater role in androgenetic hair loss than testosterone levels by themselves. The enzyme 5-alpha-reductase is necessary for this conversion. The type 2 form of the enzyme is particularly active in scalp hair follicles.(3)
Studies confirm that 5-alpha-reductase inhibitors significantly block the enzymes available to make DHT out of testosterone. This can directly affect hair loss related to these androgen hormones.(22)
Finasteride and Dutasteride Effect on DHT
Two commonly prescribed 5-alpha-reductase inhibitors are finasteride and dutasteride. Both work to reduce levels of the enzymes:(3, 22)
- In men, finasteride inhibits the type-2 version of 5α-reductase and reduces DHT levels by up to 70%.
- Dutasteride reduces both types of the enzyme for even more potent suppression of DHT.
Clinical Evidence Blocking DHT Can Help Treat Common Male Balding
In long-term, controlled 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 averages a 10% increase in number of terminal hairs is seen after about 12 months of use. Improvement usually slows down after 24 months. (22)
However, finasteride's benefits are long-lasting. Five years of treatment showed that 48% of finasteride-treated men in these clinical trials still had moderately to greatly-improved hair regrowth. Increased hair counts seen at the end of the first year remain the same after 5 years. A very small percentage (10%) had increased hair loss, and 42% were unchanged. In comparison, 75% of the placebo group showed an average 30% decrease in total hair count, with 25% unchanged.(22)
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.(22)
Clinical Evidence Blocking DHT Can Help Treat Thinning Hair in Women
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.(22, 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.(22, 30)
