Dutasteride

What it is

Dutasteride is an oral drug that inhibits both type 1 and type 2 5-alpha-reductase, the enzymes that make DHT. Finasteride blocks mainly type 2. Olsen 2006

Where it stands as of 10 October 2026:

• Japan and South Korea: prescribed for male pattern hair loss, backed by a Korean phase 3 trial Eun 2010 and a manufacturer surveillance study of 712 men. NCT01004809 A 2025 Korean trial notes it "is prescribed for male AGA in Korea and Japan". Lee 2025
• US: Avodart 0.5 mg is FDA-approved only for an enlarged prostate. Hair use is off-label and prescription-only. Avodart label
• EU and UK: authorised for an enlarged prostate; hair use is off-label. EMA 2025 A 2025 Canadian expert consensus nonetheless lists oral dutasteride among recommended treatments. Landells 2025

How it works

Blocking both enzyme types lowers DHT further than finasteride. In 399 men with prostate enlargement, serum DHT fell 94.7% on dutasteride 0.5 mg and 98.4% on 5 mg, against 70.8% on finasteride 5 mg (not a hair trial) (Clark 2004). A 1997 pharmacokinetic study found dutasteride's terminal half-life was 14 hours in rats and 65 in dogs against 1 and 4 for finasteride, and about 240 hours after a single human dose (Bramson 1997). In a 1-year trial, dutasteride 0.5 mg cut serum DHT by 94% vs 73% for finasteride 5 mg. Amory 2007 Hair response rises with dose. Olsen 2006 Its half-life is about 5 weeks, so effects, and side effects, fade slowly after the last dose. Avodart label

What the studies show

Most trials are short (24 weeks to 1 year) and many were funded by the manufacturer.

• Head to head (917 men, 24 weeks): dutasteride 0.5 mg beat finasteride 1 mg on hair count, hair width and frontal photos, with similar adverse events. Gubelin Harcha 2014
• Dose-finding (416 men, 24 weeks): hair gain rose with dose, and 2.5 mg beat finasteride 5 mg at 12 and 24 weeks. Olsen 2006
• Korean phase 3 (153 men, 6 months): +12.2 vs +4.7 hairs/cm² on placebo. Eun 2010
• Meta-analysis (3 trials, 576 men): hair count was 28.6 hairs higher than with finasteride, with no significant difference in sexual adverse events. Zhou 2019
• Open-label comparison (90 men, 24 weeks): total hairs rose from 223 to 246/cm² on dutasteride vs 227 to 231 on finasteride, and thin hairs fell from 65 to 57/cm². Shanshanwal 2017
• Identical twins (17 pairs, 1 year): the treated twin improved, and 15 of 16 pairs guessed correctly which twin was treated. Stough 2007
• Japan (120 men, 52 weeks, open label): hair count and width improved, and drug-related adverse events (17%) led to no withdrawals. Tsunemi 2016
• Lower dose (139 men, 24 weeks): 0.2 mg gained 21.5 hairs vs 6.0 on placebo and matched 0.5 mg on all endpoints. Lee 2025
• Intermittent dosing (60 men, 24 weeks): three times a week was similar to daily finasteride on hair count. Sereepanpanich 2025
• Topical (135 men, phase 2): the 0.05% solution beat oral finasteride on hair count at 24 weeks. Panuganti 2025
• Women: data are scarce; a 2024 review found only two studies that enrolled women. Almudimeegh 2024 The 2016 Cochrane review found no trials of dutasteride in female pattern loss. van Zuuren 2016

How it's used in studies

• Oral, men: 0.5 mg daily in most trials Gubelin Harcha 2014; 0.2 mg daily in a 2025 phase 3 Lee 2025; 0.5 mg two or three times a week in a small pilot. Sereepanpanich 2025
• Mesotherapy (injections into the scalp): usually every 3 months in practice. In 541 Spanish patients pain was common (45.5%), no sexual side effects were detected, and 38.4% of 86 assessable monotherapy patients had marked improvement. Saceda-Corralo 2022 Systematic reviews call the evidence promising but small and varied. Herz-Ruelas 2020; Almeziny 2025; Beer 2026
• Topical: experimental, with one phase 2 trial. Panuganti 2025
• Pipeline: CKD-843, a 3-monthly injection, is in a 288-man Korean phase 3 against oral dutasteride and placebo, with primary completion expected in September 2027. NCT06916793

Side effects and safety

• Sexual effects: in the prostate-trial data on the label (months 0 to 6), impotence was 4.7% vs 1.7%, decreased libido 3.0% vs 1.4%, and ejaculation disorders 1.4% vs 0.5%. Avodart label In young men with hair loss, sexual adverse events were 16% vs 8% on placebo over 24 weeks, and all resolved. Tsai 2018 A meta-analysis found a relative risk of 1.37 vs placebo that was not statistically significant. Lee 2019
• Mood: the EMA's 2025 review found insufficient evidence for a causal link with suicidal ideation but added precautionary mood wording. EMA 2025 See also post-finasteride syndrome.
• Fertility: over a year, semen volume fell 29.7% and total sperm count about 25 to 29%, with partial recovery 24 weeks after stopping. Amory 2007 In a Korean study of 200 men, longer use meant bigger falls in semen volume and motility, with some impairment persisting 6 months after stopping beyond roughly 18 to 20 months of use (no untreated control group). Kim 2025
• Pregnancy and blood donation: women who are or may be pregnant should not handle the capsules, and men should not donate blood until 6 months after the last dose. Avodart label
• PSA: it roughly halves within 3 to 6 months. In the REDUCE prostate trial, high-grade prostate cancer occurred in 1.0% vs 0.5% on placebo. Avodart label
• Mesotherapy risks: patchy hair loss at injection sites after a single session in 4 of 15 patients in one series, possibly from preservatives such as benzyl alcohol Chandrashekhar 2025, and persistent, partly scarring patches in 3 women. Nogueira 2026

Bottom line

Dutasteride grows more hair than finasteride over 6 to 12 months, which makes it the logical next step for men who have plateaued on finasteride and are not trying to conceive. Long-term data in men under 40 are thin, because the largest trial lasted 24 weeks, and reviewers see it mainly as a second step after finasteride. Gupta 2025 Safety is similar to finasteride plus a much longer half-life, clearer semen effects and, for injections, procedure risks. In women it is a specialist, mostly postmenopausal option, and it is contraindicated in pregnancy. Generic oral capsules are the budget-to-mid option outside Korea and Japan, where use is off-label. Discuss with a doctor.

Fun facts

• In the twin trial, 15 of 16 pairs correctly guessed which twin took dutasteride because the difference in hair was visible. Stough 2007
• Dutasteride lingers so long (half-life about 5 weeks) that men must wait 6 months after the last capsule before donating blood. Avodart label