Research briefing on adverse effects of finasteride as a treatment for hair loss

This post is more than two years old. See Temperature check on recent literature published in October 2023, and a bibliography of all systematic reviews and meta-analyses.

In the last three years, over 100 papers have been published related to adverse effects of finasteride. It can be hard to keep up with this volume of research output. This post offers highlights of two systematic reviews/meta-analyses. These types of papers select and aggregate findings across studies done in the past.

Elevated risk of sexual dysfunction

A 2019 paper reviewed 15 prior studies of finasteride taken for hair loss. The authors reported that both finasteride and dutasteride were associated with an increased risk of sexual dysfunction:

Use of 5α-reductase inhibitors carried a 1.57-fold risk of sexual dysfunction (95% confidence interval (95% CI) 1.19-2.08). The relative risk was 1.66 (95% CI 1.20-2.30) for finasteride and 1.37 (95% CI 0.81-2.32) for dutasteride… It is important that physicians are aware of, and assess, the possibility of sexual dysfunction in patients treated with 5α-reductase inhibitors.

Lee S et al. Adverse Sexual Effects of Treatment with Finasteride or Dutasteride for Male Androgenetic Alopecia: A Systematic Review and Meta-analysis. Acta Derm Venereol. 2019 Jan 1;99(1):12-17. doi:10.2340/00015555-3035. PMID:30206635.

Evidence of irreversible sexual adverse effects

The next paper is a systematic review published in a high-impact dermatology journal, Journal of the American Academy of Dermatology. The authors reviewed sexual adverse effects of a range of dermatological medications including finasteride. Consistent with the paper above, the authors find “compelling” evidence of increased rates of sexual dysfunction in patients taking finasteride:

We identified 5 studies that did not support the increased rates of sexual dysfunction in men taking 1 mg finasteride for androgenic alopecia. However, we feel that the evidence describing increased rates of sexual dysfunction is more compelling. We identified 10 studies demonstrating sexual adverse effects, including ED and decreased libido, in patients taking 1 mg finasteride.

Zakhem GA et al. Sexual dysfunction in men taking systemic dermatologic medication: A systematic review. J Am Acad Dermatol. 2019;81(1):163-172. doi:10.1016/j.jaad.2019.03.043. PMID:30905792

The authors also found 11 studies reporting irreversible adverse effects after stopping finasteride:

In studies addressing reversibility, most of these patients have resolution of sexual adverse effects after discontinuation of finasteride, and many have improvement of adverse effects over time with continued finasteride use. However, some studies describe a subset of patients with persistent adverse effects after discontinuation. Three studies identified in this review describe complete reversibility of sexual dysfunction in all patients, but 11 studies describe patients experiencing irreversible adverse effects.

Zakhem et al., 2019

To catch up on later work, see more systematic reviews and meta-analyses or a bibliography by year.