Finasteride, sold under the brand names Proscar and Propecia among others, is a medication used to treat pattern hair loss and benign prostatic hyperplasia (BPH) in men.
[24][4] In the United States, finasteride and minoxidil are the only two FDA approved drugs for the treatment of male pattern hair loss as of 2017.
[35] Finasteride has been found to be effective in the treatment of hirsutism (excessive facial and/or body hair growth) in women.
[7] Finasteride is sometimes used in hormone replacement therapy for transgender women due to its antiandrogenic effects, in combination with a form of estrogen.
[38][39] The Food and Drug Administration advises that donation of blood or plasma be deferred for at least one month after taking the last dose of finasteride.
[16][15] A 2012 update to the FDA label noted reports of decreased sex drive, problems with ejaculation and difficulty achieving an erection which continued after stopping the medication.
[39]: 16 A 2010 Cochrane review found that men taking finasteride for BPH (with a mean age of 62.4) are at increased risk for impotence, erectile dysfunction (ED), decreased libido, and ejaculation disorder for the first year of treatment.
It identified three studies that demonstrated full reversibility of side effects and eleven that described patients with irreversible adverse events.
[16] Individuals claiming to experience PFS report sexual, neurological, hormonal, and psychological side effects that persist for an extended period after stopping the drug.
[55] Reported symptoms include penile atrophy and tissue changes, decreased ejaculate volume and quality, reduced libido, erectile dysfunction, loss of penile sensitivity, decreased orgasm sensation, dry skin, metabolic changes, muscle and strength loss, gynecomastia, depression, anxiety, panic attacks, insomnia, anhedonia, concentration problems, memory impairment and suicidal ideation.
[56] A meta-analysis found a significant association between finasteride use and post-discontinuation depression, suicidal ideation, and sexual dysfunction, but the quality of evidence was limited.
[58] Some have argued that it has common features with other self-diagnosed "mystery syndromes" such as Morgellons or multiple chemical sensitivity, while others, including some in the biomedical research community, have concluded based on the available evidence, that it represents a real and serious condition.
[58] A lack of clear diagnostic criteria and the variable reporting fraction in different healthcare settings make the problem challenging to evaluate.
[56] As of 2016, Merck was a defendant in approximately 1,370 product liability lawsuits which had been filed by customers alleging they have experienced persistent sexual side effects following cessation of treatment with finasteride.
[60] In 2019, Reuters reported that faulty redactions in court documents revealed allegations from plaintiffs that Merck had known of persistent side effects in their original clinical trials but chose not to disclose them in warning labels.
[60] Finasteride has been studied in humans at single doses of up to 400 mg and at continuous dosages of up to 80 mg/day for three months, without adverse effects observed.
[5][63][64] By inhibiting these two isozymes of 5α-reductase, finasteride reduces the formation of the potent androgen dihydrotestosterone (DHT) from its precursor testosterone in certain tissues in the body such as the prostate gland, skin, and hair follicles.
[65] However, the different isozymes of 5α-reductase appear to be widely expressed, with notable tissues including the prostate gland, seminal vesicles, testes, epididymides, skin, hair follicles, liver, kidneys, and brain, among others.
[65] By inhibiting 5α-reductase and thus preventing DHT production, finasteride reduces androgen signaling in tissues like the prostate gland and the scalp.
[62][85] In 1942, James Hamilton observed that prepubertal castration prevents the later development of male pattern baldness in mature men.
She reported on a group of intersex children in the Caribbean who appeared sexually ambiguous at birth, and were initially raised as girls, but then grew external male genitalia and other masculine characteristic after onset of puberty.
These children, despite being raised as girls until puberty, were generally heterosexual and were termed "Guevedoces" by their local community, which means "penis at twelve" in Spanish.
Dr. Vagelos then sought to create a drug that could mimic the condition found in these children to treat older men who had benign prostatic hyperplasia.
[91] In 1992, finasteride (5 mg) was approved by the U.S. Food and Drug Administration (FDA) for treatment of BPH, which Merck marketed under the brand name Proscar.
[92] In 1997, Merck was successful in obtaining FDA approval for a second indication of finasteride (1 mg) for treatment of male pattern hair loss, which was marketed under the brand name Propecia.
[100] Merck was awarded a separate patent for the use of finasteride to treat pattern hair loss and it expired in November 2013.
[103] Athletes who used finasteride and were banned from international competition include skeleton racer Zach Lund, bobsledder Sebastien Gattuso, footballer Romário, and ice hockey goaltender José Théodore.
[103][104] The US Food and Drug Administration advises that donation of blood or plasma be deferred for at least one month after taking the last dose of finasteride.
[109][110] A small retrospective study reported that finasteride was effective in the treatment of acne in women with normal testosterone levels.