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

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 papers are noteworthy because they select and aggregate findings across numerous studies done in the past.

Finasteride for hair loss has an elevated risk of sexual dysfunction

The following paper, published in 2019, reviewed 15 prior studies of finasteride taken for hair loss:

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.

The paper reports 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. Both drugs were associated with an increased risk, although the increase was not statistically significant for dutasteride. As studies into dutasteride were limited, further trials are required. It is important that physicians are aware of, and assess, the possibility of sexual dysfunction in patients treated with 5α-reductase inhibitors.

Systematic review finds evidence of irreversible sexual adverse effects after discontinuing finasteride

The next paper is a systematic review published in one of the top dermatology journals, Journal of the American Academy of Dermatology. The authors reviewed sexual adverse effects of a range of dermatological medications including 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

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.

The authors also weighed evidence of adverse effects that continued (or persisted) after discontinuation of the drug. They 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.

Research on other adverse effects of finasteride continues

Research has investigated other classes of adverse effects of finasteride—primarily effects on semen, sperm and fertility; sexual function; and psychological adverse effects including suicide, suicidality and depression.

Other research looks at effects of finasteride by system such as neuroactive steroids, metabolism and others.