Weighing the risks of taking finasteride for hair loss

TLDR: Finasteride partially disables an enzyme that has an important role in hormone signaling throughout the body. Since the 1990s, there have been observations and reports of lasting sexual dysfunction in men who stopped taking finasteride. Treatment with finasteride and dutasteride can lead to changes in penile tissue as well as reduced semen quality and infertility.

Comments from urologists

Finasteride is poison ☠️

Dr. Rachel Rubin, urologist and sexual medicine specialist in December 2023. View on X

There’s significant pathology associated with finasteride… I don’t recommend it for use in any man.

Dr. Ted Schaeffer, Chair of Urology at Feinberg School of Medicine, Northwestern University in October 2023. View transcript

Key points

  1. Finasteride disrupts hormone signaling in the blood, male reproductive organs, brain, liver and other organs. Among other effects, it reduces levels of a male sex hormone called dihydrotestosterone (DHT).
  2. Some men who took finasteride and then discontinued the drug have reported severe adverse effects which do not respond to treatment, do not resolve over time, and may be irreversible.
  3. Regarding sexual dysfunction that continues after stopping finasteride:
    • The drug label includes reports of ”decrease in sex drive… problems with ejaculation… [and] difficulty in achieving an erection that continued after stopping the medication.”
    • A systematic review included 11 studies in which men experienced irreversible sexual adverse effects after stopping finasteride.
    • In clinical trials, one man discontinued the trial due to sexual dysfunction. Six months later, sexual dysfunction was still present (2007 Merck letter to the Swedish drugs regulator). At the end of treatment, 16 men still had drug-related sexual adverse events which were not resolved.
    • Post-finasteride sexual dysfunction has been reported in other clinical trials sponsored by Merck. As of 2006, Merck had received at least 100 reports of post-finasteride sexual dysfunction.
  4. Regarding semen quality and fertility:
    • A 2024 study analyzed adverse event reports submitted to FDA. The study found finasteride and dutasteride (a drug with a similar mechanism) had the strongest signal of reduced semen quality among the 40 most common drugs.
    • In a 2007 study, finasteride and dutasteride groups both had reduced sperm motility (movement) 6 months after stopping the drugs. During the trial, sperm counts in three patients dropped more than 90% from normal levels. Even 6 months after stopping the drugs, levels in all three men were more than two-thirds lower than levels before starting the trial.
    • There are no published studies of the effect of finasteride or dutasteride treatment on semen quality longer than one year.
    • A 2013 study concluded: “Finasteride should be…used with caution in men who desire fertility.” (Samplaski et al., 2013).
    • A male fertility center at Cornell advises: “Do not use finasteride (Propecia, Proscar) for hair loss. There is accumulating evidence that it negatively impacts male fertility.”
  5. Finasteride users and their doctors have reported disturbances of mental state, thought, vision, muscle tone and sleep which they linked to using finasteride. In June 2022, FDA required the addition of a warning about suicidal ideation and behavior to the Propecia label. (See a Reuters report and previous label changes)
  6. Men have reported lasting health disturbances after taking as little as one pill of finasteride.
  7. A paper found that among younger men, longer duration on finasteride was the strongest predictor of developing erectile dysfunction that continued after stopping the drug (Kiguradze et al., 2017).
  8. Animal and human research has found finasteride and dutasteride treatment are associated with changes to the penis including reduced size, increased fibrous tissue and loss of smooth muscle. Read the research
  9. In 2021, an international group of physicians and researchers published diagnostic criteria for post-finasteride syndrome (Healy et al., 2021).
  10. Since Propecia was approved by the U.S. Food and Drug Administration in 1997, the label has been revised to add new warnings at least eight times. Most recently, a warning of suicidal ideation and behavior was added.
  11. Finasteride alters levels of other steroids which support organ function.


Medical literature as well as Merck records, firsthand reports, adverse event reports to FDA, physician perspectives and the drug label.

Selected medical literature

Diviccaro S, Melcangi RC, Giatti S. Post-finasteride syndrome: an emerging clinical problem. Neurobiol Stress. 2019. DOIPubMed

Healy D, Bahrick A, Bak M, et al. Diagnostic criteria for enduring sexual dysfunction after treatment with antidepressants, finasteride and isotretinoin. Int J Risk Saf Med. 2021. DOIPubMed

Khera M, Than JK, Anaissie J, et al. Penile vascular abnormalities in young men with persistent side effects after finasteride use for the treatment of androgenic alopecia. Transl Androl Urol. 2020. DOIPubMed

Kiguradze T, Temps WH, Yarnold PR, et al. Persistent erectile dysfunction in men exposed to the 5α-reductase inhibitors, finasteride, or dutasteride. PeerJ. 2017. DOIPubMed

Leliefeld HHJ, Debruyne FMJ & Reisman Y. The post-finasteride syndrome: possible etiological mechanisms and symptoms. Int J Impot Res. 2023. doi:10.1038/s41443-023-00759-5PubMed

Schifano N, Capogrosso P, Boeri L, et al. Are finasteride-related penile curvature/Peyronie’s disease adverse event reports worthy of further clinical investigation? Disproportionality analysis based on both the Food and Drug Administration (FDA) and the European Medicines Agency (EMA) pharmacovigilance databases. Int J Impot Res. 2023. DOI • PubMed

Tan H, Luo L, Li W, et al. A pharmacovigilance study of drug-reduced male semen quality based on the Food and Drug Administration adverse event reporting system database. Andrology. 2024. doi:10.1111/andr.13668 • PubMed

See more papers on 5-alpha syndrome