Dutasteride

• A 24-week randomized, placebo-controlled trial by Olsen (2006) enrolled 416 men aged 21 to 45. Men took dutasteride 0.05, 0.1, 0.5 or 2.5 mg a day, finasteride 5 mg or placebo. Target-area hair count rose with the dutasteride dose, and 2.5 mg beat finasteride at 12 and 24 weeks (PMID: 17110217).
• In a 6-month randomized, double-blind phase 3 trial by Eun (2010) in 153 Korean men aged 18 to 49, hair count rose 12.2 hairs per square centimeter on dutasteride 0.5 mg against 4.7 on placebo (p=0.0319), with no major difference in adverse events (PMID: 20605255).
• Gubelin Harcha (2014) reported a 24-week randomized, double-blind phase 3 trial in 917 men aged 20 to 50. Men took dutasteride 0.02, 0.1 or 0.5 mg, finasteride 1 mg or placebo. Hair count and width rose with the dutasteride dose; the primary endpoint, hair count in a 2.54-cm circle at week 24, was higher with dutasteride 0.5 mg than with finasteride (p=0.003) and placebo (p<0.001), and adverse events were similar across groups (PMID: 24411083).
• In a 24-week randomized, open-label, evaluator-blinded trial by Shanshanwal (2017) in 90 men aged 18 to 40 in Mumbai, total hair count per square centimeter rose from 223 to 246 with dutasteride 0.5 mg and from 227 to 231 with finasteride 1 mg, thin hairs fell more with dutasteride, and side effects were similar (PMID: 27549867).
• Stough (2007) ran a 1-year randomized, double-blind trial in 17 pairs of identical twins. One twin in each pair took dutasteride 0.5 mg and the other placebo; investigator and self-assessments favored dutasteride, and in 15 of the 16 pairs that finished, the twins correctly guessed who had taken the drug (PMID: 17348989).
• In a 24-week randomized, single-blind trial by Poostiyan (2026) in 46 Iranian men aged 20 to 50, hair density and thickness improved with both dutasteride 0.5 mg and finasteride 1 mg, with no significant difference between them; PSA fell only with dutasteride (PMID: 42466626).
• In a 24-week randomized, double-blind phase 3 trial by Lee (2025), 139 Korean men were analyzed. Men took dutasteride 0.2 mg, placebo or dutasteride 0.5 mg in a 2:2:1 ratio. Vertex hair count rose 21.53 with 0.2 mg against 5.96 with placebo (p=0.0072), and 0.2 mg matched 0.5 mg on every efficacy endpoint; the sponsoring company designed the trial and collected and analyzed the data (PMID: 40736519).

Pooled analyses

Three of the network meta-analyses below come from Aditya Gupta and colleagues in Ontario, Canada: the 2013 analysis from the University of Toronto, and the 2022 and 2025 analyses from Mediprobe Research in London, Ontario (PMID: 23768246, PMID: 35107565, PMID: 40586152).

• In a 2019 meta-analysis by Zhou of 3 head-to-head trials with 576 men, the change in total hair count favored dutasteride over finasteride (mean difference 28.57), with no significant difference in sexual side effects (PMID: 30863034).
• In a 2022 network meta-analysis of 23 studies by Gupta and colleagues, dutasteride 0.5 mg a day gave the largest rise in total hair count at 24 weeks, 7.1 hairs per square centimeter more than finasteride 1 mg (95 percent confidence interval 5.1 to 9.3) (PMID: 35107565).
• In Gupta's 2013 network meta-analysis, finasteride 1 mg, finasteride 5 mg and dutasteride 0.5 mg did not differ significantly from each other in efficacy, and none differed from placebo in sexual dysfunction (PMID: 23768246).
• A 2025 network meta-analysis of 33 studies by Gupta and colleagues ranked dutasteride 0.5 mg a day as the most effective option, and dutasteride given by mesotherapy was significantly less effective than the oral drug (PMID: 40586152).

Long-term and real-world data

• A 52-week open-label study by Tsunemi (2016) followed 120 Japanese men (NCT01831791). 110 men finished; drug-related adverse events occurred in 17 percent; hair count, hair width and global appearance improved from baseline (PMID: 26893187).
• Choi (2016) described Korean post-marketing surveillance of 712 men from July 2009 to July 2013. Adverse drug reactions were reported in 9.3 percent, and physicians rated 78.6 percent as improved (PMID: 27489426).
• In a 2024 retrospective study by Choi of 99 Korean men treated for at least 5 years, investigators rated 89.9 percent as improved; there was no control group (PMID: 38321615).

Women

Evidence in women is limited to non-randomized oral data and scalp injection studies. In a retrospective sample of 60 women drawn from a database of 3,500 treated women, hair thickness rose in 83.3 percent after 3 years of dutasteride 0.15 mg a day, without a control group (PMID: 25382509). In a controlled study of 126 women in Cairo with female pattern hair loss, photographic improvement after 12 sessions of mesotherapy with a dutasteride-containing preparation was seen in 62.8 percent, against 17.5 percent with saline injections (PMID: 22486925).

Mesotherapy and topical delivery

A 2025 systematic review found that studies of dutasteride injected into the scalp reported gains in hair density and thickness with mostly mild local side effects, but the studies were small and varied in method (PMID: 41367323). In an uncontrolled pilot of 20 adults with hair loss that had not responded to standard treatment, a dutasteride gel delivered with skin patting and iontophoresis was followed by gains in hair density and shaft diameter measured 8 weeks after four monthly sessions (PMID: 40900274).

Prostate trials

• In three pooled 2-year placebo-controlled trials in 4,325 men with benign prostatic hyperplasia, reported by Roehrborn (2002), serum DHT fell 90.2 percent and prostate volume 25.7 percent, and the risks of acute urinary retention and prostate surgery fell 57 and 48 percent against placebo (PMID: 12350480).
• In CombAT, a 4-year trial in 4,844 men, dutasteride plus tamsulosin beat tamsulosin alone, but not dutasteride alone, on the primary endpoint of acute urinary retention or prostate surgery (PMID: 19825505).
• The 4-year REDUCE trial included 6,729 men with a biopsy or prostate surgery. Biopsy-detected prostate cancer fell 22.8 percent relative to placebo, but Gleason 8 to 10 tumors in years 3 and 4 numbered 12 against 1 (PMID: 20357281).

Hormone and body-composition studies

• A 20-week randomized trial by Bhasin (2012) enrolled 139 healthy men aged 18 to 50. The men's own testosterone production was suppressed with monthly leuprolide injections, and they received graded weekly testosterone enanthate doses with dutasteride 2.5 mg a day or placebo; gains in fat-free mass, and changes in strength, sexual function, prostate volume, sebum and hematocrit, did not differ with dutasteride (PMID: 22396515).
• In a 1-year randomized trial by Amory (2007) in 99 healthy men, dutasteride 0.5 mg lowered DHT by 94 percent and reduced total sperm count, semen volume and sperm motility (PMID: 17299062).

Guidelines and consensus statements

Japan's 2017 guideline lists oral finasteride, oral dutasteride and topical 5 percent minoxidil as first-line treatments for male pattern hair loss (PMID: 29863806); see BodyHackGuide's minoxidil guide. A 2025 Canadian Delphi consensus of 11 physicians, with four coauthors from a cosmetics company, recommended oral dutasteride and listed intradermal dutasteride among interventions recommended with near consensus (PMID: 40986632).

In Korean post-marketing surveillance of 712 men aged 18 to 41, 9.3 percent reported adverse drug reactions, most often decreased libido (1.3 percent), indigestion (1.1 percent) and impotence (1.0 percent), with breast enlargement (gynecomastia) in 0.3 percent (PMID: 27489426). A 52-week Japanese study of 120 men recorded drug-related adverse events in 17 percent, and none led to withdrawal (PMID: 26893187).

Data from the prostate trials

In pooled 2-year placebo-controlled trials in more than 4,300 men with benign prostatic hyperplasia, impotence was reported in 4.7 percent on dutasteride against 1.7 percent on placebo in the first 6 months, decreased libido in 3.0 against 1.4 percent, ejaculation disorders in 1.4 against 0.5 percent, and breast enlargement or tenderness in 0.5 against 0.2 percent (US prescribing information for Avodart). The label states that these sexual adverse reactions may persist after treatment stops and that the role of dutasteride in this persistence is unknown (US prescribing information for Avodart). Reports after approval include hypersensitivity reactions with angioedema and serious skin reactions, male breast cancer, depressed mood, and testicular pain and swelling (US prescribing information for Avodart).

Semen and fertility

In a one-year trial in 99 healthy men, dutasteride 0.5 mg lowered total sperm count by 28.6 percent at 26 weeks and semen volume by 29.7 percent at 52 weeks, and sperm motility fell 6 to 12 percent; 24 weeks after stopping, total sperm count was 23.3 percent below baseline, a difference the authors did not find statistically significant (PMID: 17299062). The US label describes a 52-week study in healthy volunteers and states that the effect on total sperm count was not reversible after 24 weeks of follow-up, with 2 men showing falls of more than 90 percent at 52 weeks and partial recovery afterward (US prescribing information for Avodart).

Mood

In an Ontario cohort of 93,197 men aged 66 or older starting finasteride or dutasteride for prostate enlargement, suicide risk did not rise, but self-harm (hazard ratio 1.88) and depression (hazard ratio 1.94) were more frequent in the first 18 months, depression stayed somewhat more frequent after that (hazard ratio 1.22), and the type of drug did not change these associations (PMID: 28319231). Two later meta-analyses, of 5 and 9 studies, found no statistically significant association between 5-alpha-reductase inhibitors and depression, suicide or other neuropsychiatric events (PMID: 38692949, PMID: 42890027).

Prostate cancer grade and PSA

In the 4-year REDUCE trial, dutasteride lowered the rate of prostate cancer found on biopsy, but tumors with a Gleason score of 8 to 10 in years 3 and 4 numbered 12 on dutasteride against 1 on placebo (PMID: 20357281). The US label carries a warning that dutasteride may increase the risk of high-grade prostate cancer, and notes that it lowers serum PSA by about 50 percent within 3 to 6 months (US prescribing information for Avodart).

Cardiac failure signal

In REDUCE, the composite category of cardiac failure occurred in 0.7 percent of men on dutasteride against 0.4 percent on placebo (PMID: 20357281), and the 4-year CombAT trial also showed an imbalance in cardiac failure across its three arms (PMID: 19825505); the US label states that no causal relationship has been established (US prescribing information for Avodart).

Injections into the scalp

Case series describe new patches of hair loss at injection sites after dutasteride mesotherapy: 4 of 15 patients treated at a clinic in Bengaluru, India developed nonscarring patches after a single session, and 3 women in another series did not fully regrow their hair (PMID: 41346555, PMID: 41779759). The Indian authors suggested that two ingredients of the injected mixture, benzyl alcohol and polysiloxane, may have contributed through cytotoxic effects (PMID: 41346555).