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. Finasteride and dutasteride have been associated with penile abnormalities including growth of fibrous tissue and loss of smooth muscle. Taking finasteride can affect semen quality and fertility. There is no known effective treatment for lasting dysfunctions after stopping finasteride.
Sources: Merck records, firsthand reports, adverse event reports to FDA, published research, physician perspectives, the drug label and personal experience. These points concern finasteride as a treatment for hair loss in younger men.
- Finasteride disrupts hormone signaling in the blood, testes, liver, brain and other organs. Among other effects, it reduces levels of a male sex hormone called dihydrotestosterone (DHT).
- 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. See firsthand experiences and adverse event data.
- Regarding sexual dysfunction that persists after stopping finasteride:
- The drug label approved by the U.S. Food & Drug Administration includes reports of sexual adverse effects that “continued after stopping the medication.”
- A systematic review included 11 studies which described men experiencing irreversible sexual adverse effects after stopping finasteride.
- In Merck Phase 3 clinical trials of finasteride for hair loss, 16 men had drug-related sexual adverse events which were not resolved at the end of treatment. In addition, there was one man who discontinued the trial due to a drug-related sexual adverse event, and it was not resolved six months after discontinuing treatment (2007 Merck letter to Swedish regulatory authority).
- In another Merck-sponsored clinical trial, one man’s drug-related sexual adverse experience on finasteride did not resolve with continued treatment (Overstreet et al., 1999).
- Beyond sexual dysfunction, men have reported disturbances of mental state, thought, vision, muscle tone and sleep, that continue after stopping finasteride.
- Currently, there is no test that could predict the risk of developing lasting dysfunctions after stopping finasteride or dutasteride (another drug with a similar pharmacology). There is no known effective treatment for these lasting dysfunctions. Men have reported lasting dysfunctions after taking as little as one pill of finasteride.
- 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).
- Animal and human research has found finasteride and dutasteride treatment is associated with changes to the penis including reduced size, increased fibrous tissue and loss of smooth muscle. Read the research
- Regarding semen, sperm and fertility:
- In a clinical trial, men who took finasteride (5 mg) for six months had reduced sperm count, concentration, motility (movement) and semen volume. After one year of treatment, three of these four parameters returned to normal range; however, sperm motility did not return to normal range. Nearly six months after stopping treatment, sperm motility remained lower than before starting finasteride treatment. (Amory et al., 2007).
- The only clinical trial of effects of finasteride (1 mg) on semen parameters lasted less than a year (48 weeks) (Overstreet et al., 1999). There are no published trials on long-term effects of finasteride use on semen parameters or fertility.
- 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 recommends (emphasis added): “Do not use finasteride (Propecia, Proscar) for hair loss. There is accumulating evidence that it negatively impacts male fertility.”
- In June 2021, FDA added a new adverse event to the Postmarketing Experience section of the finasteride 1 mg label: hematospermia, or blood in semen.
- There have been reports to FDA of malformed embryos and spontaneous abortion following paternal exposure to finasteride (Zakhem et al., 2019). The review noted: “…spontaneous abortion has been frequently reported to the FDA following paternal exposure and may be a risk associated [with] finasteride use.”
- In 2021, an international group of physicians and researchers published diagnostic criteria for post-finasteride syndrome (Healy et al., 2021).
- Since Propecia was approved by the U.S. Food and Drug Administration in 1997, safety concerns have emerged in adverse event data and medical literature. The label has been revised to add new warnings at least eight times. Most recently, a warning of suicidal ideation and behavior was added.
- Drug information: Finasteride label • Dutasteride label • Mechanism of finasteride • How was finasteride invented?
- Clinical perspective: Doctors expressing concerns
- Research: Alterations to penile and prostatic tissue • Research by system & function
- Data & experiences: Adverse event data • Firsthand experiences
- Lasting dysfunctions: 5-alpha syndrome (post-finasteride syndrome)
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. DOI • PubMed
Leliefeld HHJ, Debruyne FMJ & Reisman Y. The post-finasteride syndrome: possible etiological mechanisms and symptoms. Int J Impot Res. 2023. doi:10.1038/s41443-023-00759-5
Saengmearnuparp T, Lojanapiwat B, Chattipakorn N, Chattipakorn S. The connection of 5-alpha reductase inhibitors to the development of depression. Biomed Pharmacother. 2021. DOI • PubMed • Full text via ScienceDirect
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. 2022. DOI • PubMed
Sung HH, Yu J, Kang SJ, et al. Persistent erectile dysfunction after discontinuation of 5-alpha reductase inhibitor therapy in rats depending on the duration of treatment. World J Mens Health. 2019. DOI • PubMed