The safety and efficacy of finasteride for transgender men with androgenetic alopecia: a case series.

BACKGROUND: Testosterone replacement therapy is commonly used in transgender men for masculinization. One of the most common adverse effects of testosterone replacement therapy is androgenetic alopecia. In Japan, finasteride is approved exclusively for cisgender men and is not indicated for transgender men. The aim of this clinical trial was to evaluate the safety and efficacy of finasteride in transgender men with androgenetic alopecia. CASE PRESENTATION: This study included three transgender men (assigned female at birth, identifying as male), aged 44, 43, and 29 years. All participants were of Asian ethnicity. A clinical trial was conducted from October 2021 to December 2023. Transgender men aged 20-60 years who had not undergone hysterectomy, were undergoing testosterone replacement therapy, and who had been diagnosed with stage ≥ II androgenetic alopecia on the basis of the Norwood-Hamilton scale were recruited. The participants initiated treatment with 0.2 mg of finasteride per day for 3 months (phase 1). If no adverse events above grade 2 occurred, the dose was increased to 1.0 mg per day for an additional 3 months (phase 2). The primary endpoints were the incidence of treatment-related adverse events at 1 week, 1 month, and 3 months, as well as the rate of participants continuing treatment at 3 months. None of the patients experienced serious adverse events at 3 months, and all the patients extended their treatment to a total of 6 months. Improvements of at least one stage on the N-H scale were observed, but two participants experienced resumption of menstruation. CONCLUSION: Finasteride appears to be a safe and effective treatment for androgenetic alopecia in transgender men undergoing testosterone replacement therapy. However, its potential for reducing some of the effects of testosterone replacement therapy warrants further investigation. TRIAL REGISTRATION: jRCT, jRCTs061210040, registered 7 October 2021, https://jrct.mhlw.go.jp/latest-detail/jRCTs061210040 .