Finasteride, sold under the brand names Proscar (5 mg) and Propecia (1 mg) among others, is a medication used to treat pattern hair loss and benign prostatic hyperplasia (BPH). It can also be used to treat excessive hair growth in women. It is usually taken orally but there are topical formulations for patients with hair loss, designed to minimize systemic exposure by acting specifically on hair follicles.
Along with dutasteride, finasteride is a widely dispensed 5α-reductase inhibitor. As such, it is an antiandrogen that works by decreasing the production of dihydrotestosterone (DHT) by about 70% in serum, 65-70% in scalp skin, 90% in prostate.
In addition to DHT, finasteride also inhibits the production of several anticonvulsant neurosteroids including allopregnanolone, androstanediol, and tetrahydrodeoxycorticosterone.
Adverse effects from finasteride are rare in men with already enlarged prostates; 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 2023, it was the 91st most commonly prescribed medication in the United States, with more than 7million prescriptions.
Medical uses Finasteride has been used for the treatment of symptomatic benign prostatic hyperplasia (BPH) and for the treatment of male pattern hair loss.
Enlarged prostate Physicians sometimes prescribe finasteride for the treatment of benign prostatic hyperplasia, 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.
The use of the drug showed significant sexual adverse effects such as erectile dysfunction and less sexual desire, in particular when obstructive symptoms due to an enlarged prostate were present.
Pattern hair loss Finasteride is also used to treat male pattern baldness (androgenic alopecia), a condition that develops in up to 80% of Caucasian men aged 70 and over. 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. Two meta-analyses found finasteride's efficacy caused about 15% hair regrowth. Specifically oral finasteride was observed to regrow about 18 hair follicles in a square centimeter area of scalp. In comparison a full head of hair usually has 120 hair follicles per square centimeter scalp.
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. Finasteride is less effective in the treatment of scalp hair loss than dutasteride.
Prostate cancer In males aged 55 years old and over finasteride decreases the risk of low-grade prostate cancer but may increase the risk of high-grade prostate cancer and has no effect on overall survival.
A 2010 review found a 25% reduction in the risk of prostate cancer with 5α-reductase inhibitors. 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 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 of bodily hirsutism after 2 years of treatment. Other studies using finasteride for hirsutism have also found it to be effective.
Transgender hormone therapy Finasteride is sometimes used as an antiandrogen in feminizing hormone therapy for transfeminine people. There are limited clinical data on finasteride for this use and some authorities explicitly recommend against its routine use. Relatedly, the medication is considered to be limitedly useful and unnecessary in transfeminine people with testosterone levels in the normal female range. However, finasteride may be helpful in those with higher testosterone levels and symptoms like scalp hair loss and excessive body hair or who seek only partial feminization.
Besides transfeminine people, finasteride is helpful in transmasculine people for preventing scalp hair loss and is better-established for this purpose, though it might impede masculinization such as clitoral growth and development of facial and body hair.
Adverse effects A 2010 Cochrane review of finasteride for BPH found that, in men with a weighted mean age of 62.4, adverse effects are rare in men with already enlarged prostates; "nevertheless, men taking finasteride are at increased risk for impotence, erectile dysfunction, decreased libido, and ejaculation disorder, versus placebo." , fresh evidence suggested such effects, along with disturbed neurosteroid production, may persist after finasteride use is stopped.
Finasteride is contraindicated in pregnancy. The US Food and Drug Administration (FDA) 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.FDA. Posted 9 June 2011. 5-alpha reductase inhibitors (5-ARIs): Label Change – Increased Risk 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.Medicines and Healthcare products Regulatory Agency Drug Safety Update. December 2009 Finasteride: potential risk of male breast cancer 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.
Sexual adverse effects Use of finasteride is associated with an increased risk of sexual dysfunction including erectile dysfunction, decreased libido and ejaculatory dysfunction. Sexual adverse effects of finasteride and dutasteride have been linked to lower quality of life and ability to maintain an intimate relationship, and can cause stress in relationships.
The adverse effect profiles of finasteride are somewhat different for its indications of hair loss and BPH.
Finasteride for androgenetic alopecia (hair loss in men) The most common adverse effects of finasteride taken for hair loss are a decrease in sex drive, erectile dysfunction, and a decrease in the amount of semen.
In addition, finasteride has been reported in case reports to cause sexual problems that persist after stopping the medication. 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. The update also referenced reports of testicular pain and "male infertility and/or poor quality of semen."
In 2025, the European Medicines Agency confirmed that suicidal thoughts can occur as a side effect of the hair-loss treatment finasteride and similar dutasteride. The majority of these reports involved patients taking the 1 mg dosage, typically prescribed for androgenetic alopecia, a hormone-related form of hair loss. However, the agency noted that the precise frequency of this adverse effect could not be determined from the data available. In October 2024, the EMA had initiated a review of both finasteride and dutasteride due to concerns over potential links to suicidal ideation. While finasteride—marketed by Organon as Propecia—already includes warnings about possible psychiatric effects, the EMA stated that the evidence did not support a similar link for dutasteride, sold by GSK under the brand name Avodart.
Finasteride for benign prostatic hyperplasia The most common adverse sexual effects of finasteride for BPH are: trouble getting or keeping an erection, decrease in sex drive, decreased volume of ejaculate, and ejaculation disorders.
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. The rates became indistinguishable from placebo after 2–4 years and these side effects usually got better over time.
Long-term Finasteride may cause persistent adverse sexual, neurological, and physical effects in a subset of men. A 2019 systematic review surveyed the literature on the reversibility of finasteride's side effects. It identified three studies that demonstrated full reversibility of side effects and eleven that described patients with irreversible adverse events. A separate 2017 retrospective review of nearly 12,000 patients found 1.4% developed persistent (lasting at least 90 days after stopping Finasteride) ED, with this dropping to 0.8% for 16-42 year olds.
Post-finasteride syndrome Reports of long-term, post-discontinuation adverse effects in some fraction of former finasteride users have led to a proposed post-finasteride syndrome (PFS), although some within the medical community question whether there is enough evidence to support a causal relationship between finasteride usage and persistent symptoms.
Individuals claiming to experience PFS report sexual, neurological, hormonal, and psychological side effects that persist for an extended period after stopping the drug. 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. 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.