Finasteride:
what the research shows

How it works

Finasteride is a type 2 5-alpha-reductase inhibitor. It decreases the formation of DHT from testosterone, and that is the reason it is used for male pattern hair loss. It does not add hair in the way a growth stimulant would; it slows the process that shrinks the follicle.

Which dose

In the dose-ranging studies, men aged 18 to 36 with moderate hair loss were given 5, 1, 0.2 or 0.01 mg a day, or placebo. Efficacy was shown at 0.2 mg or more; 1 mg and 5 mg were similar and superior to the lower doses; 0.01 mg was similar to placebo. The authors chose 1 mg a day as the optimal dose. In a network meta-analysis of 23 studies, dutasteride 0.5 mg gave 7.1 hairs/cm² more than finasteride 1 mg at 24 weeks (95% CI 5.1 to 9.3). The 0.5 mg capsule in our catalog was not one of the doses in these trials; the physician sets the dose for each person.

Time course

Hair loss is slow, and so is the response. A 24-month analysis of men aged 18 to 60 found significant hair growth against placebo in every scalp area at 24 months. Over five years of pooled trial data, finasteride 1 mg made further visible hair loss 93% less likely than placebo (95% CI 89 to 97%) in 1,553 men. These figures describe the likelihood of further loss, not a percentage of regrowth.

Who has been studied

The placebo-controlled work is in men with male pattern hair loss: the dose-ranging studies enrolled men aged 18 to 36, the 24-month analysis men aged 18 to 60. A five-year open series of 801 Japanese men evaluated after 903 were started found that 99.4% improved on photographic assessment, and that starting at 40 or older and a more advanced Norwood stage predicted a weaker response. We found no trial of finasteride for male pattern hair loss in women.

Sexual side effects, in brief

The 24-month analysis reported a slightly higher rate of drug-related sexual adverse experiences with finasteride than with placebo. A 2011 series of 71 men aged 21 to 46 who stopped after persistent sexual symptoms described low libido, erectile dysfunction and reduced arousal. That series was self-selected from reports, so it shows the risk exists, not how common it is. The full side-effect discussion is in our finasteride side-effects article.

What this does not say

• These are averages from trials of finasteride 1 mg a day, not predictions for one person.
• We found no placebo-controlled trial longer than two years. Five-year and Japanese figures come from pooled or open series.
• Compounded versions were not studied, and the topical and combination products in our catalog were not tested in these trials.

Sources

1. 1.Roberts JL et al. Clinical dose ranging studies with finasteride, a type 2 5alpha-reductase inhibitor, in men with male pattern hair loss. J Am Acad Dermatol 1999;41(4):555-63. Journal of the American Academy of Dermatology
2. 2.Kaufman KD et al. Global photographic assessment of men aged 18 to 60 years with male pattern hair loss receiving finasteride 1 mg or placebo. J Am Acad Dermatol 2012. Journal of the American Academy of Dermatology
3. 3.Kaufman KD et al. Long-term treatment with finasteride 1 mg decreases the likelihood of developing further visible hair loss in men with androgenetic alopecia. Eur J Dermatol 2008;18(4):400-6. European Journal of Dermatology
4. 4.Yoshitake T et al. Five-year efficacy of finasteride in 801 Japanese men with androgenetic alopecia. J Dermatol 2015;42(7):735-8. Journal of Dermatology
5. 5.Irwig MS, Kolukula S. Persistent sexual side effects of finasteride for male pattern hair loss. J Sex Med 2011;8(6):1747-53. Journal of Sexual Medicine
6. 6.Gupta AK et al. Relative efficacy of minoxidil and the 5-alpha reductase inhibitors in androgenetic alopecia treatment of male patients: a network meta-analysis. JAMA Dermatol 2022;158(3):266-74. JAMA Dermatology