|Trade names||Proscar, Propecia, Finide, others|
|Other names||MK-906; YM-152; L-652,931; 17β-(N-tert-Butylcarbamoyl)-4-aza-5α-androst-1-en-3-one; N-(1,1-Dimethylethyl)-3-oxo-4-aza-5α-androst-1-ene-17β-carboxamide|
|Drug class||5α-Reductase inhibitor|
|Metabolism||Liver (CYP3A4, ALDH)|
|Elimination half-life||Adults: 5–6 hours|
Elderly: >8 hours
|CompTox Dashboard (EPA)|
|Chemical and physical data|
|Molar mass||372.553 g·mol−1|
|3D model (JSmol)|
Finasteride, sold under the brand names Proscar and Propecia among others, is a medication used to treat an enlarged prostate or hair loss in men. It can also be used to treat excessive hair growth in women and as a part of hormone therapy for transgender women. It is taken by mouth.
Finasteride is a 5α-reductase inhibitor and therefore an antiandrogen. It works by decreasing the production of dihydrotestosterone (DHT) by about 70%, including in the prostate gland and the scalp.
Side effects from finasteride are rare, however some men experience sexual dysfunction, depression, and breast enlargement. In some men, sexual dysfunction may persist after stopping the medication. It may also hide the early symptoms of certain forms of prostate cancer.
Finasteride was patented in 1984 and approved for medical use in 1992. It is available as a generic medication. In 2017, it was the 86th-most commonly prescribed medication in the United States, with more than nine million prescriptions.
Finasteride is indicated for the treatment of symptomatic benign prostatic hyperplasia (BPH) in men with an enlarged prostate  and for the treatment of male pattern hair loss (androgenetic alopecia) in men.
Physicians sometimes prescribe finasteride for the treatment of benign prostatic hyperplasia (BPH), informally known as an enlarged prostate. Finasteride may improve the symptoms associated with BPH such as difficulty urinating, getting up during the night to urinate, hesitation at the start and end of urination, and decreased urinary flow. It provides less symptomatic relief than alpha-1 blockers such as tamsulosin and symptomatic relief is slower in onset (six months or more of treatment with finasteride may be required to determine the therapeutic results of treatment).[medical citation needed] Symptomatic benefits are mainly seen in those with prostate volume > 40 cm3.[medical citation needed] In long-term studies finasteride but not alpha-1 inhibitors reduce the risk of acute urinary retention (−57% at 4 years) and the need for surgery (−54% at 4 years).[medical citation needed] If the drug is discontinued, any therapeutic benefits are reversed within about 6–8 months.
Scalp hair loss
Finasteride is also used to treat male pattern baldness (androgenic alopecia) in men, a condition that develops in up to 80% of Caucasian men. 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. Treatment with finasteride slows further hair loss and provides about 30% improvement in hair loss after six months of treatment, with effectiveness persisting as long as the drug is taken. Taking finasteride leads to a reduction in scalp and serum DHT levels; by lowering scalp levels of DHT, finasteride can maintain or increase the amount of terminal hairs in the anagen phase by inhibiting and sometimes reversing miniaturization of the hair follicle. Finasteride is most effective on the crown but can reduce hair loss in all areas of the scalp. Finasteride has also been tested for pattern hair loss in women; however, the results were no better than placebo.
A 2010 review found a 25% reduction in the risk of prostate cancer with 5α-reductase inhibitor. A follow-up study of the Medicare claims of participants in a 10-year Prostate Cancer Prevention Trial suggests the reduction in prostate cancer is maintained even after discontinuation of treatment. However, 5α-reductase inhibitors have been found to increase the risk of developing certain rare but aggressive forms of prostate cancer (27% risk increase), although not all studies have observed this. No impact of 5-α-reductase inhibitor on survival has been found in people with prostate cancer.
Excessive hair growth
Finasteride has been found to be effective in the treatment of hirsutism (excessive facial and/or body hair growth) in women. In a study of 89 women with hyperandrogenism due to persistent adrenarche syndrome, finasteride produced a 93% reduction in facial hirsutism and a 73% reduction bodily hirsutism after 2 years of treatment. Other studies using finasteride for hirsutism have also found it to be clearly effective.
Transgender hormone therapy
Finasteride is sometimes used in hormone replacement therapy for transgender women due to its antiandrogenic effects, in combination with a form of estrogen. However, little clinical research of finasteride use for this purpose has been conducted and evidence of safety or efficacy is limited. Moreover, caution has been recommended when prescribing finasteride to transgender women, as finasteride may be associated with side effects such as depression, anxiety, and suicidal ideation, symptoms that are particularly prevalent in the transgender population and in others at high risk already.
A 2010 Cochrane review concluded that adverse effects from finasteride are rare when used for BPH. When finasteride was originally approved for hair loss in 1997, the FDA reported that it appeared well tolerated, with the most common side effects being related to sexual function. Finasteride is contraindicated in pregnancy. 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.
The FDA has added a warning to 5α-reductase inhibitors concerning an increased risk of high-grade prostate cancer, as the treatment of BPH lowers PSA (prostate-specific antigen), which could mask the development of prostate cancer. Although overall incidence of male breast cancer in clinical trials for finasteride 5 mg was not increased, there are post-marketing reports of breast cancer in association with its use, though available evidence does not provide clarity as to whether there is a causative relationship between finasteride and these cancers. A 2018 meta-analysis found no higher risk of breast cancer with 5α-reductase inhibitors. Some men develop gynecomastia (breast development or enlargement) following finasteride usage. The risk of gynecomastia with 5α-reductase inhibitors is low at about 1.5%. Depressive symptoms and suicidality have been reported.
Finasteride causes short-term sexual dysfunction in some men, which may persist in some men after stopping the medication. There are case reports of persistent diminished libido or erectile dysfunction after stopping the drug and the FDA has updated the label to inform people of these reports.
The 2010 Cochrane review found that compared with placebo, men taking finasteride are at increased risk for impotence, erectile dysfunction, decreased libido, and ejaculation disorder for the first year of treatment. The rates became indistinguishable from placebo after 2–4 years and these side effects usually got better over time. A 2016 meta-analysis found that sexual dysfunction, including erectile dysfunction, loss of libido, and reduced ejaculate, may occur in 3.4 to 15.8% of men treated with finasteride or dutasteride. This adverse effect has been linked to lower quality of life and can cause stress in relationships.
Finasteride may cause persistent adverse sexual, neurological and physical effects in a subset of men. This has been called post-finasteride syndrome, characterized by reported sexual and physical symptoms such as loss of libidio, erectile dysfunction, ejaculatory disorders, reduction in penis size, penile curvature, reduced sensation, male breast enlargement, muscular atrophy, fatigue and severely dry skin. People with post-finasteride syndrome may experience depression and anxiety, cognitive impairment and suicidal thoughts.
Post-finasteride syndrome may also have reduced levels of neurosteroids such as allopregnanolone in their cerebrospinal fluid. One study found that 1.4% developed persistent sexual dysfunction.
A 2019 Reuters investigation showed that Merck found evidence of persistent side effects in their original clinical trials and did not disclose it in their warning label. They uncovered court filings which demonstrated that Merck misrepresented Propecia's safety record following clinical trials in the mid-late 1990s.
In one deposition, Charlotte Merritt, who oversaw regulatory activity for Propecia, acknowledged that Merck changed Propecia's label for sexual adverse events in 2002, four years after Propecia hit the market. The label changed from “resolution occurred in all men who discontinued therapy with Propecia ” to “resolution occurred in men who discontinued therapy with Propecia”. Merritt testified that Merck eliminated the word “all” due to evidence from the clinical trials of adverse events that did not resolve following discontinuation of use. In another deposition, Paul Howes, the head of marketing for Propecia acknowledged that Merck was aware that warnings of sexual side effects, particularly persistent to permanent side effects, would have a devastating impact on sales.
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. There is no specific recommended antidote for finasteride overdose.
Finasteride is a 5α-reductase inhibitor. It is specifically a selective inhibitor of the type II and III isoforms of the enzyme. 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. As such, finasteride is a type of antiandrogen, or more specifically, an androgen synthesis inhibitor. However, some authors do not define finasteride as an "antiandrogen," a term which can refer more specifically to antagonists of the androgen receptor.
Finasteride results in a decrease of circulating DHT levels by about 65 to 70% with an oral dosage of 5 mg/day and of DHT levels in the prostate gland by up to 80 to 90% with an oral dosage of 1 or 5 mg/day. In parallel, circulating levels of testosterone increase by approximately 10%, while local concentrations of testosterone in the prostate gland increase by about 7-fold and local testosterone levels in hair follicles increase by around 27 to 53%. An oral dosage of finasteride of only 0.2 mg/day has been found to achieve near-maximal suppression of DHT levels (68.6% for 0.2 mg/day relative to 72.2% for 5 mg/day). Finasteride does not completely suppress DHT production because it lacks significant inhibitory effects on the 5α-reductase type I isoenzyme, with more than 100-fold less inhibitory potency for type I as compared to type II (IC50 = 313 nM and 11 nM, respectively). This is in contrast to inhibitors of all three isoenzymes of 5α-reductase like dutasteride, which can reduce DHT levels in the entire body by more than 99%. In addition to inhibiting 5α-reductase, finasteride has also been found to competitively inhibit 5β-reductase (AKR1D1). However, its affinity for the enzyme is substantially less than for 5α-reductase (an order of magnitude less than for 5α-reductase type I) and hence is unlikely to be of clinical significance.
As of 2012, the tissues in which the different isozymes of 5α-reductase are expressed are not fully clear. This is because different investigators have obtained varying results with different reagents, methods, and tissues examined. 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.
By inhibiting 5α-reductase and thus preventing DHT production, finasteride reduces androgen signaling in tissues like the prostate gland and the scalp. In the prostate, this reduces prostate volume, which improves BPH and reduces risk of prostate cancer. Finasteride reduces prostate volume by 20 to 30% in men with benign prostatic hyperplasia. Inhibition of 5α-reductase also reduces epididymal weight, and decreases motility and normal morphology of spermatozoa in the epididymis.
Neurosteroids like 3α-androstanediol (derived from DHT) and allopregnanolone (derived from progesterone) activate the GABAA receptor in the brain; because finasteride prevents the formation of neurosteroids, it functions as a neurosteroidogenesis inhibitor and may contribute to a reduction of GABAA activity. Reduction of GABAA receptor activation by these neurosteroids has been implicated in depression, anxiety, and sexual dysfunction.
The mean oral bioavailability of finasteride is approximately 65%. The absorption of finasteride is not affected by food. At steady-state with 1 mg/day finasteride, mean peak concentrations of finasteride were 9.2 ng/mL (25 nmol/L). Conversely, following a single 5 mg dose of finasteride, mean peak levels of finasteride were 37 ng/mL (99 nmol/L), and plasma concentrations increased by 47 to 54% following 2.5 weeks of continued daily administration. The volume of distribution of finasteride is 76 L. Its plasma protein binding is 90%. The drug has been found to cross the blood–brain barrier, whereas levels in semen were found to be undetectable.
Finasteride is extensively metabolized in the liver, first by hydroxylation via CYP3A4 and then by aldehyde dehydrogenase. It has two major metabolites, which are the tert-butyl side chain monohydroxylated and monocarboxylic acid metabolites. These metabolites show approximately 20% of the inhibitory activity of finasteride on 5α-reductase. Hence, the metabolites of finasteride are not particularly active. The drug has a terminal half-life of 5 to 6 hours in adult men (18–60 years of age) and a terminal half-life of 8 hours or more in elderly men (more than 70 years of age). It is eliminated as its metabolites 57% in the feces and 40% in the urine.
Finasteride, also known as 17β-(N-tert-butylcarbamoyl)-4-aza-5α-androst-1-en-3-one, is a synthetic androstane steroid and 4-azasteroid. It is an analogue of androgen steroid hormones like testosterone and DHT. As an unconjugated steroid, finasteride is a highly lipophilic compound.
In 1942, James Hamilton observed that prepubertal castration prevents the later development of male pattern baldness in mature men. In 1974, Julianne Imperato-McGinley of Cornell Medical College in New York attended a conference on birth defects. 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. Her research group found these children shared a genetic mutation, causing deficiency of the 5α-reductase enzyme and male hormone dihydrotestosterone (DHT), which was found to have been the etiology behind abnormalities in male sexual development. Upon maturation, these individuals were observed to have smaller prostates which were underdeveloped, and were also observed to lack incidence of male pattern baldness.
In 1975, copies of Imperato-McGinley's presentation were seen by P. Roy Vagelos, who was then serving as Merck's basic-research chief. He was intrigued by the notion that decreased levels of DHT led to the development of smaller prostates. Dr. Vagelos then sought to create a drug which could mimic the condition found in these children to treat older men who were suffering from benign prostatic hyperplasia.
Finasteride was developed by Merck under the code name MK-906. A team led by chemist Gary Rasmusson and biologist Jerry Brooks developed potential 5α-reductase inhibitors based on transition state inhibitors, using an iterative process of molecular design, testing, and redesign. 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. Rasmusson and Brooks were awarded IPO's “Inventor of the Year” award in 1993 for their work on finasteride. 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. It was the first 5α-reductase inhibitor to be introduced and was followed by dutasteride in 2001. The first study of finasteride in the treatment of hirsutism in women was published in 1994.
Society and culture
Finasteride is the generic name of the drug and its INN, USAN, BAN, and JAN, while finastéride is its DCF. It is also known by its former developmental code names MK-906, YM-152, and L-652,931.
Finasteride is marketed primarily under the brand names Propecia, for pattern hair loss, and Proscar, for BPH, both of which are products of Merck & Co. There is 1 mg of finasteride in Propecia and 5 mg in Proscar. Merck's patent on finasteride for the treatment of BPH expired in June 2006. Merck was awarded a separate patent for the use of finasteride to treat pattern hair loss and it expired in November 2013. Finasteride is also marketed under a variety of other brand names throughout the world.
Men in the U.S. and Canada concerned about persistent sexual side effects "coined the phrase 'post-finasteride syndrome', which they say is characterized by sexual, neurological, hormonal and psychological side effects that can persist in men who have taken finasteride for hair loss or an enlarged prostate". In 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.
From 2005 to 2009, the World Anti-Doping Agency banned finasteride because it was discovered that the drug could be used to mask steroid abuse. It was removed from the list effective January 1, 2009, after improvements in testing methods made the ban unnecessary. 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.
The U.S. 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. The UK also has a one-month deferral period.
Preliminary research suggests that topical finasteride may be effective in the treatment of pattern hair loss. Topical finasteride, like the oral preparation, reduces serum DHT. However, studies have shown that the extent of the reduction of serum DHT is less with the topical application.
DHT may be involved in the cause of acne, and 5α-reductase inhibitors might be effective in the treatment of the condition. A small retrospective study reported that finasteride was effective in the treatment of acne in women with normal testosterone levels. A randomized controlled trial found that finasteride was less effective than flutamide or an ethinylestradiol/cyproterone acetate birth control pill in the treatment of acne in women with high androgen levels.
Androgens and estrogens may be involved in the cause of hidradenitis suppurativa (acne inversa). Two case series have reported that finasteride is effective in the treatment of hidradenitis suppurativa in girls and women.
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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 CAPSULE SUMMARY d Prescription medications are a common cause of sexual dysfunction. Possible sexual adverse effects should be discussed with men using these medications. d We identified evidence for sexual adverse effects in patients taking 11 systemic dermatologic medications. Level 1 evidence evaluating sexual dysfunction as a primary outcome was available for finasteride.
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[...] caution is recommended while prescribing oral finasteride to male-to-female transsexuals, as the drug has been associated with inducing depression, anxiety and suicidal ideation, symptoms that are particularly common in patients with gender dysphoria, who are already at a high risk.
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