Finasteride for hair loss: how it works, how long it takes, and the side effects

Source · Organon · The official US label of the original finasteride brand for hair loss. Its trial figures come from the manufacturer's own studies in men aged 18 to 41; the prostate figures come from trials of the 5 mg tablet (Proscar) in older men. Archived as the full label text from the DailyMed XML (copied from the dht-blockers archive).

• Finasteride blocks one of the two enzymes (type II 5-alpha-reductase) that turn testosterone into DHT. “Finasteride is a competitive and specific inhibitor of Type II 5α-reductase, an intracellular enzyme that converts the androgen testosterone into DHT.”
• Balding scalp holds more DHT than scalp with hair. “In men with male pattern hair loss (androgenetic alopecia), the balding scalp contains miniaturized hair follicles and increased amounts of DHT compared with hairy scalp.”
• Within a day, a 1 mg tablet cuts the DHT in the blood by about two-thirds (65%). “Finasteride produces a rapid reduction in serum DHT concentration, reaching 65% suppression within 24 hours of oral dosing with a 1-mg tablet.”

Source · Organon · The official US label of the original finasteride brand for hair loss. Its trial figures come from the manufacturer's own studies in men aged 18 to 41; the prostate figures come from trials of the 5 mg tablet (Proscar) in older men. Archived as the full label text from the DailyMed XML (copied from the dht-blockers archive).

• The dose is one 1 mg tablet a day, with or without food. “PROPECIA may be administered with or without meals. The recommended dose of PROPECIA is one tablet (1 mg) taken once daily.”

Source · Drake L (University of Oklahoma), Hordinsky M, Fiedler V, et al. · 249 men, scalp biopsies before and after 42 days of finasteride at five doses (0.01 to 5 mg) or placebo. It measured DHT, not hair. Abstract quoted; it lists only the first author's affiliation (copied from the dht-blockers archive).

• 1 mg lowered DHT in the blood by 71.4%; 0.2 mg already by 68.6%. “Serum DHT levels declined significantly (P <.001) by 49.5%, 68.6%, 71.4%, and 72.2% in the 0.05, 0.2, 1, and 5 mg finasteride treatment groups, respectively.”
• Doses from 0.2 mg a day already gave the full drop in scalp and blood DHT. “In this study, doses of finasteride as low as 0.2 mg per day maximally decreased both scalp skin and serum DHT levels.”

Source · Organon · The official US label of the original finasteride brand for hair loss. Its trial figures come from the manufacturer's own studies in men aged 18 to 41; the prostate figures come from trials of the 5 mg tablet (Proscar) in older men. Archived as the full label text from the DailyMed XML (copied from the dht-blockers archive).

• It usually takes three months or more of daily use before there is a benefit. “In general, daily use for three months or more is necessary before benefit is observed.”
• If you stop, the effect is gone within 12 months. “Withdrawal of treatment leads to reversal of effect within 12 months.”

Source · Organon · The official US label of the original finasteride brand for hair loss. Its trial figures come from the manufacturer's own studies in men aged 18 to 41; the prostate figures come from trials of the 5 mg tablet (Proscar) in older men. Archived as the full label text from the DailyMed XML (copied from the dht-blockers archive).

• An independent panel judging photos saw more hair in 48% of men on finasteride at 12 months (7% on placebo) and in 66% at 2 years (7% on placebo). “At 12 months, 48% of men treated with PROPECIA had an increase as compared with 7% of men treated with placebo. At 2 years, an increase in hair growth was demonstrated in 66% of men treated with PROPECIA, compared with 7% of men treated with placebo.”
• At 5 years, the panel rated 48% of men on finasteride as having more hair, 42% unchanged and 10% as having lost hair; on placebo it was 6%, 19% and 75%. “At 5 years, 48% of men treated with PROPECIA demonstrated an increase in hair growth, 42% were rated as having no change (no further visible progression of hair loss from baseline) and 10% were rated as having lost hair when compared to baseline. In comparison, 6% of men treated with placebo demonstrated an increase in hair growth, 19% were rated as having no change and 75% were rated as having lost hair when compared to baseline.”
• By hair counts over 5 years, every man left on placebo lost hair, against 35% of men on finasteride. “At 5 years, 100% of men in the placebo group demonstrated hair loss, compared with 35% of men treated with PROPECIA.”
• The front-of-scalp trial counted hairs in the mid-front area, not in the temples or the hairline itself. “Hair counts were obtained in the anterior mid-scalp area, and did not include the area of bitemporal recession or the anterior hairline.”

Source · Kaufman KD (Merck Research Laboratories), Olsen EA, Whiting D, et al. · The two placebo-controlled trials behind finasteride's approval for hair loss: 1,553 men aged 18 to 41 with hair loss on the crown, 1 year plus a 1-year extension. Run by the manufacturer (first author at Merck). Abstract quoted (copied from the dht-blockers archive).

• 1,553 men took finasteride 1 mg or placebo; 1,215 carried on for a second year. “In two 1-year trials, 1553 men (18 to 41 years of age) with male pattern hair loss received oral finasteride 1 mg/d or placebo, and 1215 men continued in blinded extension studies for a second year.”
• On finasteride, hair counts in a 1-inch circle on the crown were 107 hairs higher than placebo at 1 year and 138 at 2 years (from about 876 at the start). “Clinically significant increases in hair count (baseline = 876 hairs), measured in a 1-inch diameter circular area (5.1 cm2) of balding vertex scalp, were observed with finasteride treatment (107 and 138 hairs vs placebo at 1 and 2 years, respectively; P < .001).”
• On placebo, hair loss kept going. “Treatment with placebo resulted in progressive hair loss.”

Source · Finasteride Male Pattern Hair Loss Study Group · The same two trials followed for up to five years, with placebo-controlled extensions each year. The study group ran the manufacturer's trials; the abstract names no individual authors or funding. Abstract quoted.

• Of the 1,553 men in the first-year trials, 1,215 continued in up to four more placebo-controlled years. “1,553 men with MPHL were randomized to receive finasteride 1 mg/day or placebo, and 1,215 men continued in up to four 1-year, placebo-controlled extension studies.”
• Over five years, finasteride gave lasting improvement while men on placebo kept losing hair. “Treatment with finasteride led to durable improvements in scalp hair over five years”
• No new safety problems were seen with long-term use. “Finasteride was generally well tolerated and no new safety concerns were identified during long-term use.”

Source · Leyden J (University of Pennsylvania), Dunlap F, Miller B, et al. · The third approval trial: men with thinning at the front and middle of the scalp, 1 year against placebo and a 1-year open extension. The abstract gives no number of men (the US label says 326) and no funding statement. Abstract quoted.

• Hair counts in the front of the scalp rose significantly on finasteride. “There was a significant increase in hair count in the frontal scalp of finasteride-treated patients (P < .001)”
• The effect held or improved in the second year. “Efficacy was maintained or improved throughout the second year of the study.”
• The authors conclude it slowed hair loss and increased growth in the front and middle of the scalp. “In men with hair loss in the anterior/mid area of the scalp, finasteride 1 mg/day slowed hair loss and increased hair growth.”

Source · Rossi A, Cantisani C, Scarnò M, et al. (Sapienza University of Rome) · 118 men aged 20 to 61 at one Italian university clinic, followed for 10 years on finasteride 1 mg and judged on standardized photos. No placebo group, so it shows how treated men did over time, not how much was due to the drug. Abstract quoted.

• 118 men aged 20 to 61 took part; there was no comparison group. “118 men, between 20 and 61 years, with AGA receiving finasteride (1 mg/day), were enrolled in this uncontrolled study.”
• Men over 30 did better: 42.8% of those aged 20 to 30 had not improved even after 10 years. “Better improvements are observed in patients older than 30 years (42.8% aged between 20 and 30 years did not improve also after 10 years)”
• For 21%, staying on it beyond 5 years gave better results. “In 21% of cases, the treatment continuation beyond 5 years provided better results.”
• 6% reported side effects. “Side effects were referred by 6% of the patients”
• The authors say the result after the first year helps predict how well it will work, and that many men unchanged at 1 year improved later. “In our opinion, the result after the first year can help in predicting the effectiveness of the treatment. Its efficacy was not reduced as time goes on; in fact, a big proportion of subjects unchanged after 1 year, improved later on, maintaining a positive trend.”

Source · Organon · The official US label of the original finasteride brand for hair loss. Its trial figures come from the manufacturer's own studies in men aged 18 to 41; the prostate figures come from trials of the 5 mg tablet (Proscar) in older men. Archived as the full label text from the DailyMed XML (copied from the dht-blockers archive).

• In year 1 of the trials (945 men on finasteride, 934 on placebo): lower sex drive 1.8% vs 1.3%, erection problems 1.3% vs 0.7%, ejaculation problems 1.2% vs 0.7%. “PROPECIA N=945 Placebo N=934 Decreased Libido 1.8 1.3 Erectile Dysfunction 1.3 0.7 Ejaculation Disorder (Decreased Volume of Ejaculate) 1.2 (0.8) 0.7 (0.4)”
• Any of these sexual side effects: 3.8% on finasteride against 2.1% on placebo. They went away in men who stopped and in most who carried on. “Integrated analysis of clinical adverse experiences showed that during treatment with PROPECIA, 36 (3.8%) of 945 men had reported one or more of these adverse experiences as compared to 20 (2.1%) of 934 men treated with placebo (p=0.04). Resolution occurred in men who discontinued therapy with PROPECIA due to these side effects and in most of those who continued therapy.”
• By the fifth year of treatment, each of these was reported by 0.3% of men or fewer. “The incidence of each of the above adverse experiences decreased to ≤0.3% by the fifth year of treatment with PROPECIA.”
• 1.4% of men on finasteride stopped because of a side effect thought to be drug-related, against 1.6% on placebo. “1.4% of patients taking PROPECIA (n=945) were discontinued due to adverse experiences that were considered to be possibly, probably or definitely drug-related (1.6% for placebo; n=934).”
• Doctors are told to ask patients to report breast changes such as lumps, pain or nipple discharge. “Physicians should instruct their patients to promptly report any changes in their breasts such as lumps, pain or nipple discharge.”

Source · Złotowska A, Jastrząb-Miśkiewicz B, Krajewski PK (Wrocław) · A systematic review of studies of sexual side effects of finasteride and dutasteride in people treated for hair loss. The authors declare no conflicts. Abstract quoted (copied from the dht-blockers archive).

• Across placebo-controlled trials of 1 mg tablets, 1.9-6.7% of men reported sexual side effects, against 0.9-3.9% on placebo; most were mild and went away after stopping. “Across placebo-controlled RCTs evaluating oral finasteride 1 mg in men with AGA, sexual adverse events were reported in 1.9-6.7% of treated patients compared with 0.9-3.9% in placebo groups, with most events mild and reversible upon discontinuation.”
• Topical finasteride 0.25%: 2.8% against 4.8% for the tablets. “Topical finasteride 0.25% was associated with lower rates of sexual adverse events (2.8%) compared with oral finasteride (4.8%).”
• The authors: most sexual side effects in the trials were infrequent, mild and reversible, but individual risk varies. “Overall, clinicians should counsel patients that most sexual side effects reported in controlled AGA studies are infrequent, mild, and reversible, but individual susceptibility varies.”
• They call for better long-term studies with standard definitions of sexual dysfunction and of persistence. “further high-quality long-term studies-using standardized definitions of sexual dysfunction and persistence-are needed to quantify risks better and identify vulnerable subgroups.”

Source · Organon · The official US label of the original finasteride brand for hair loss. Its trial figures come from the manufacturer's own studies in men aged 18 to 41; the prostate figures come from trials of the 5 mg tablet (Proscar) in older men. Archived as the full label text from the DailyMed XML (copied from the dht-blockers archive).

• The reports collected since approval are voluntary, so the label says they can't show how often a problem happens or prove the drug caused it. “Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure”
• Those reports include sexual problems that continued after stopping. “sexual dysfunction that continued after discontinuation of treatment, including erectile dysfunction, libido disorders, ejaculation disorders, and orgasm disorders”
• They also include male infertility or poorer semen quality, which improved or returned to normal after stopping in some reports. “male infertility and/or poor seminal quality (normalization or improvement of seminal quality has been reported after discontinuation of finasteride)”
• And depression, suicidal thoughts and behaviour. “Nervous System/Psychiatric: depression, suicidal ideation and behavior.”

Source · European Medicines Agency (PRAC, CMDh) · The EU regulator's page on its 2025 review of finasteride and dutasteride and suicidal thoughts, started at the request of the French medicines agency. Its safety committee (PRAC) made the recommendations, the CMDh endorsed them on 19 June 2025 and the European Commission's decision of 22 August 2025 applies in all EU countries. A regulator's conclusion, not a study. Archived as the page text (HTML kept) on 2026-10-18.

• After an EU-wide review, suicidal thoughts were confirmed as a side effect of finasteride 1 mg and 5 mg tablets; how often it happens can't be estimated from the data. “Suicidal ideation was confirmed as a side effect of finasteride 1 and 5 mg tablets by the PRAC, following an EU-wide review of available data on these medicines. The frequency of the side effect is unknown, meaning that it is not possible to estimate it from available data.”
• Most of the cases were in people taking 1 mg for hair loss. “Most cases of suicidal ideation were reported in people using 1 mg finasteride tablets”
• The advice to patients: if your mood changes on 1 mg for hair loss, stop taking it and contact your doctor as soon as possible. “If you are taking finasteride 1 mg tablets for hair loss and you experience any mood changes, stop taking finasteride and contact your doctor for further medical advice as soon as possible.”
• Sexual problems on finasteride may contribute to mood changes; see a doctor if you have them. “In some patients taking 1 mg finasteride tablets, problems with sexual function (such as less desire to have sex, difficulty having an erection and problems with ejaculation) may contribute to mood changes, including suicidal thoughts. If you experience problems with sexual function, contact your doctor for further medical advice.”
• Packs of 1 mg tablets in the EU are to include a patient card about these risks. “If you are taking 1 mg finasteride tablets, you will receive a patient card in the package informing you about these risks and what action to take if you experience symptoms of mood change or problems with sexual function.”
• No link was found between suicidal thoughts and the finasteride skin spray. “Based on the available evidence, no link could be found between suicidal thoughts and the use of either finasteride as a skin spray (to treat hair loss) or dutasteride capsules (to treat benign prostatic hyperplasia).”
• The committee concluded that the benefits still outweigh the risks for all approved uses. “concluded that the benefits of finasteride and dutasteride medicines continue to outweigh their risks for all approved uses”

Source · Nguyen DD, Marchese M, Cone EB, et al. (Brigham and Women's Hospital, Harvard Medical School) · An analysis of side-effect reports in VigiBase, the WHO's global database of suspected adverse reactions (data from June 2019). It compares how often a problem is reported for finasteride against other drugs; it cannot show how often the problem occurs or that the drug caused it. One author reported fees from drug companies outside this work. Abstract quoted.

• The database held 356 reports of suicidality and 2,926 of psychological side effects in people taking finasteride. “VigiBase contained 356 reports of suicidality and 2926 reports of psychological adverse events (total of 3282 adverse events of interest) in finasteride users”
• Such reports were more common than expected in men under 45 using it for hair loss. “significant RORs of suicidality and psychological adverse events were associated with finasteride use in patients younger than 45 years who used finasteride for alopecia.”
• No such signal was found in older men using it for an enlarged prostate. “such signals were not detected in older patients with BPH”
• The authors say this may come from stimulated reporting (people reporting more once a problem is known) and/or from younger patients being more vulnerable. “The sensitivity analyses suggest that these disproportional signals of adverse events may be due to stimulated reporting and/or younger patients being more vulnerable to finasteride's adverse effects.”

Source · Organon · The official US label of the original finasteride brand for hair loss. Its trial figures come from the manufacturer's own studies in men aged 18 to 41; the prostate figures come from trials of the 5 mg tablet (Proscar) in older men. Archived as the full label text from the DailyMed XML (copied from the dht-blockers archive).

• It is approved for men only. “PROPECIA® is indicated for the treatment of male pattern hair loss (androgenetic alopecia) in MEN ONLY.”
• Women who are or may become pregnant must not take it: it can harm a male fetus. “Finasteride use is contraindicated in women when they are or may potentially be pregnant.”
• Pregnant women, or women who may become pregnant, should not handle crushed or broken tablets; whole tablets are coated and safe to handle. “Women should not handle crushed or broken PROPECIA tablets when they are pregnant or may potentially be pregnant because of the possibility of absorption of finasteride and the subsequent potential risk to a male fetus. PROPECIA tablets are coated and will prevent contact with the active ingredient during normal handling, provided that the tablets have not been broken or crushed.”
• In 137 women past menopause with pattern hair loss, finasteride did no better than placebo over 12 months. “In a study involving 137 postmenopausal women with androgenetic alopecia who were treated with PROPECIA (n=67) or placebo (n=70) for 12 months, effectiveness could not be demonstrated.”

Source · Hu AC, Chapman LW, Mesinkovska NA (University of California) · A systematic review of 65 studies (1997-2017) of finasteride in women, for hair loss and other conditions. Abstract quoted (copied from the dht-blockers archive).

• 65 studies with 2,683 women. “A total of 2,683 patients participated in 65 studies involving finasteride use in women published between January 1997 and July 2017.”
• For female pattern hair loss, studies other than randomised trials say finasteride 'may' help. “Other prospective and retrospective studies report that finasteride may improve hair loss in women with female pattern hair loss or frontal fibrosing alopecia.”

Source · Organon · The official US label of the original finasteride brand for hair loss. Its trial figures come from the manufacturer's own studies in men aged 18 to 41; the prostate figures come from trials of the 5 mg tablet (Proscar) in older men. Archived as the full label text from the DailyMed XML (copied from the dht-blockers archive).

• In men aged 18 to 41 on 1 mg, the average PSA fell from 0.7 to 0.5 ng/mL after 12 months. “In clinical studies with PROPECIA (finasteride, 1 mg) in men 18-41 years of age, the mean value of serum prostate specific antigen (PSA) decreased from 0.7 ng/mL at baseline to 0.5 ng/mL at Month 12.”
• In older men taking the 5 mg prostate tablet, PSA is lowered by about 50%. “in clinical studies with PROSCAR (finasteride, 5 mg) when used in older men who have benign prostatic hyperplasia (BPH), PSA levels are decreased by approximately 50%.”
• Any confirmed rise in PSA while on finasteride should be checked, even if the value is still in the normal range. “Any confirmed increase in PSA while on PROPECIA may signal the presence of prostate cancer and should be evaluated, even if those values are still within the normal range for men not taking a 5α-reductase inhibitor”
• In a 7-year trial of men aged 55 and over on 5 mg a day (5 times the hair-loss dose), high-grade (Gleason 8-10) prostate cancer was found in 1.8% against 1.1% on placebo. “Men aged 55 and over with a normal digital rectal examination and PSA ≤3.0 ng/mL at baseline taking finasteride 5 mg/day (5 times the dose of PROPECIA) in the 7-year Prostate Cancer Prevention Trial (PCPT) had an increased risk of Gleason score 8-10 prostate cancer (finasteride 1.8% vs placebo 1.1%).”

Source · Piraccini BM, Blume-Peytavi U, Scarci F, et al. (seven of the ten named authors at Almirall, the maker of the spray) · 458 men at 45 European sites, 24 weeks: finasteride spray on the scalp, finasteride tablets or placebo. Seven of the ten named authors work at the drug company Almirall. Abstract quoted (copied from the dht-blockers archive).

• 323 of the 458 men completed the study. “Of 458 randomized patients, 323 completed the study and 446 were evaluated for safety.”
• On the spray, hair counts rose more than on placebo (about 20 against 7 hairs in the target area) and about as much as on the tablets. “Change from baseline in target area hair count (TAHC) at week 24 (primary efficacy endpoint) was significantly greater with topical finasteride than placebo (adjusted mean change 20.2 vs. 6.7 hairs; P < 0.001), and numerically similar between topical and oral finasteride.”
• Side effects on the spray did not differ meaningfully from placebo. “Incidence and type of adverse events, and cause of discontinuation, did not differ meaningfully between topical finasteride and placebo.”
• The spray still lowered blood DHT, by about a third, against just over half with the tablets. “reduction from baseline in mean serum DHT concentration was lower (34.5 vs. 55.6%), with topical vs. oral finasteride”

Source · Zhou C (Peking University People's Hospital), Yang B, Zeng H, et al. · 270 men at 16 sites in China, 24 weeks: finasteride spray once a day or placebo (2 to 1). Supported by the company Cutia Therapeutics, two of whose staff are among the authors. Abstract quoted.

• 270 men were randomised; 251 completed the study. “A total of 270 individuals were enrolled and randomized, and 251 completed the study (165 in topical finasteride group, 86 in placebo group).”
• Hair counts on the spray were significantly higher than placebo at 24 weeks, but only numerically higher at 12 weeks. “the change from baseline in target area hair count was significantly higher at week 24 ( P <0.05), although it was only numerically higher at week 12 ( P = 0.0688).”
• The study was supported by the company Cutia Therapeutics. “This study was supported by Cutia Therapeutics (Wuxi) Co., Ltd, Wuxi, China.”