Peptide & experimental

Dutasteride

Q: Does dutasteride work better than finasteride against hair loss?

In a blinded study with 917 men, dutasteride increased hair count and hair thickness more than finasteride 1 mg after 24 weeks. A network meta-analysis of 23 studies reached a similar result. The comparison was not tested for longer than 24 weeks.

Q: Is dutasteride approved for hair loss?

Not in Germany. Here, dutasteride is approved only for symptoms caused by benign prostate enlargement; for hair loss it is an off-label use. In Japan and South Korea it is approved for hair loss in men.

Q: What side effects does dutasteride have?

The best known are sexual side effects such as erectile dysfunction and reduced libido; in a study in men with hair loss they occurred in 16 %, compared with 8 % under placebo. In addition, dutasteride halves the PSA value, and since 2025 the product information has contained a warning about mood changes.

Q: Does the Dear Healthcare Professional Letter on suicidal thoughts also apply to dutasteride?

The Dear Healthcare Professional Letter (Rote-Hand-Brief) of September 15, 2025 concerns finasteride and dutasteride. For dutasteride, a link with suicidal thoughts could not be demonstrated; the warning was added as a precaution because it works via the same mechanism as finasteride.

Q: Why should women not touch dutasteride capsules?

Dutasteride is absorbed through the skin and can disrupt the development of the external genitalia in male fetuses. Women, children and adolescents should therefore not touch leaking capsules and should wash affected skin immediately with soap and water.

Q: How long does dutasteride stay in the body?

The half-life is 3 to 5 weeks. According to the summary of product characteristics, the PSA value returns to baseline within 6 months of discontinuation.

5-alpha reductase inhibitor (type I and II), prescription-only · Avodart, Zagallo, Dutasteride

Dutasteride inhibits both enzymes that convert testosterone into DHT and thereby lowers the hormone more strongly than finasteride. In blinded studies over 24 weeks, more hair grew under it than under placebo and than under finasteride. In Germany, however, it is approved only for benign prostate enlargement; for hair loss it is an off-label use, unlike in Japan and South Korea. On top of this come a half-life of weeks and the same warnings as for finasteride.

What dutasteride is

Dutasteride is a prescription-only inhibitor of 5-alpha reductase that blocks both forms of the enzyme, type I and type II. In Germany it is approved as Avodart for moderate to severe symptoms caused by benign prostate enlargement (BPH) and to reduce the risk of urinary retention and surgery in this condition. The approved dose is one 0.5 mg capsule daily.

Its close relative is finasteride, which inhibits only type II and is approved for hair loss in Germany. Dutasteride is prescribed off-label for hair loss; a 2022 network meta-analysis compares it with finasteride and minoxidil. What is rated is the state of knowledge: good data on the prostate from more than two decades, several blinded studies on hair, each over 24 weeks.

How it works

5-alpha reductase converts testosterone into dihydrotestosterone (DHT), the hormone that makes hair follicles shrink in hereditary hair loss. Dutasteride inhibits both forms of the enzyme. In men with prostate enlargement, blood DHT fell by a median of 94 % after one year at the approved dose, and testosterone rose by 19 %.

In a study with 416 men with hair loss, DHT in the scalp and blood fell with increasing dose, and hair count rose accordingly. The half-life is 3 to 5 weeks; the active substance therefore remains in the body long after the last capsule.

What is well supported

More hair than under finasteride. In a blinded study with 917 men aged 20 to 50, dutasteride at the prostate dose increased hair count and hair thickness after 24 weeks more than finasteride 1 mg (p = 0.003 and p = 0.004) and than placebo (p < 0.001). Side effects were similar between the groups.
The effect depends on the dose. In 416 men, hair count rose with the dose; scalp and blood DHT fell accordingly.
Also confirmed against placebo alone. In a Korean phase III study with 153 men, hair count rose by 12.2 per square centimeter after six months, compared with 4.7 under placebo (p = 0.0319).
Ahead when pooled. In a network meta-analysis of 23 studies, dutasteride showed the largest increase in total hair count after 24 weeks, 7.1 hairs per square centimeter more than finasteride 1 mg.
Approved elsewhere. In Japan, dutasteride has been approved for hereditary hair loss in men since 2015; the Japanese review report also mentions an approval for this in South Korea.

What the studies show

Gubelin Harcha 2014: the direct comparison with finasteride

Gubelin Harcha 2014 (J Am Acad Dermatol) assigned 917 men aged 20 to 50 to dutasteride at three doses, finasteride 1 mg or placebo, over 24 weeks. Hair count and hair thickness rose with the dutasteride dose. At the prostate dose, dutasteride was ahead of finasteride and placebo in hair count, hair thickness and the frontal photo assessment. The number and severity of side effects were similar in all groups. The study ran for only 24 weeks.

Olsen 2006: dose and DHT

Olsen 2006 (J Am Acad Dermatol) gave 416 men aged 21 to 45 dutasteride at four doses, finasteride 5 mg or placebo for 24 weeks. Hair count rose in a dose-dependent manner; the highest dutasteride dose tested was superior to finasteride after 12 and 24 weeks. DHT in the scalp and blood fell and testosterone rose, each depending on the dose.

Tsai 2018: sexual side effects

Tsai 2018 (J Dermatol) specifically monitored 117 men with hair loss for sexual side effects: 24 weeks of blinded dutasteride or placebo, followed by 24 weeks of open-label dutasteride. In the blinded phase, erectile dysfunction, loss of libido or ejaculation disorders occurred in 16 % under dutasteride and in 8 % under placebo. All were mild to moderate and resolved during or after treatment. The study was small.

REDUCE 2010: prostate cancer

The REDUCE trial (N Engl J Med 2010) gave men aged 50 to 75 with elevated PSA and an unremarkable prior biopsy dutasteride or placebo for four years. Cancer was found in 659 of 3,305 men under dutasteride and in 858 of 3,424 under placebo, a relative reduction of 22.8 %. In years 3 and 4, however, 12 high-grade tumors (Gleason 8 to 10) occurred under dutasteride, compared with one under placebo (p = 0.003). Heart failure as a composite category was more frequent under dutasteride (0.7 % versus 0.4 %).

The European review procedure 2025

In 2025, the European Medicines Agency reviewed suicidal thoughts under finasteride and dutasteride. Of 325 case reports, 13 concerned dutasteride, one of them both substances. A link with dutasteride could not be established from the data; because it works via the same mechanism, a warning about mood changes was added to the product information as a precaution.

Where the data stop

How long the effect lasts. The blinded hair studies ran for 24 weeks, the Korean study for six months. Hair data measured over years are not available from these studies.
Safety in young men. The large long-term data come from men over fifty with prostate enlargement. How well they can be transferred to young men with hair loss is open.
Mood and suicidal thoughts. For dutasteride, a link has not been demonstrated, but it has not been ruled out either. The warning in the product information applies as a precaution.
The comparison in the meta-analysis. The network meta-analysis partly compares indirectly across different studies. Dutasteride was tested directly against finasteride 1 mg in one large study.

Status, approval and legal

In Germany, dutasteride is prescription-only and approved as Avodart 0.5 mg only for symptoms caused by benign prostate enlargement. For hair loss it is an off-label use. It is contraindicated in women, children and adolescents.

In Japan, dutasteride was approved in 2015 as Zagallo for hereditary hair loss in men; the Japanese review report mentions an approval for this use in South Korea as well.

On September 15, 2025, a joint Dear Healthcare Professional Letter (Rote-Hand-Brief) on finasteride and dutasteride was issued, coordinated with the European Medicines Agency and the German Federal Institute for Drugs and Medical Devices (BfArM). Since then, the product information for dutasteride has contained a warning about depressed mood, depression and suicidal thoughts that were reported under another 5-alpha reductase inhibitor.

Safety

The summary of product characteristics names erectile dysfunction and reduced libido as side effects. In the study in men with hair loss, sexual side effects occurred twice as often under dutasteride as under placebo (16 % versus 8 %) and resolved. In a study in 27 healthy men, sperm count, ejaculate volume and motility fell by 23, 26 and 18 % after one year.

Dutasteride can disrupt the development of the external genitalia in male fetuses. Because it is absorbed through the skin, women, children and adolescents should not touch leaking capsules; if the partner is pregnant, a condom is recommended.

The PSA value falls by about half after six months and must be reassessed. In REDUCE, more high-grade prostate tumors occurred; according to the summary of product characteristics, their connection with dutasteride is not clear. Reports of breast cancer in men exist; epidemiological studies showed no increased risk. Anyone who notices depressed mood or suicidal thoughts should seek medical advice; in Germany, the Telefonseelsorge crisis line can be reached free of charge around the clock at 0800 111 0 111.

The safety value of 8 in the BK-Score rates the state of the data, not the danger.

BK-Score Supported, with caveats

Human evidence		7
Mechanism		9
Safety data		8
Hype gap		6
Track record of use		8

Evidence 7, because three blinded studies with almost 1,500 men in total show more hair growth – in the largest, with 917 men, also compared with finasteride 1 mg (Gubelin Harcha 2014; Olsen 2006; Eun 2010) – but each only over 24 weeks. Mechanism 9, because the inhibition of both 5-alpha reductases and the lowering of DHT in blood and scalp have been measured in humans. Safety 8, because the side effects are well documented from large prostate studies such as REDUCE and from the 2025 European review procedure; for young men with hair loss there are fewer long-term data, and the axis rates the state of the data, not the danger. Hype 6, because the advertised lead over finasteride is supported by a direct study and a network meta-analysis, but was measured only over 24 weeks. Use 8, because dutasteride has been used for prostate enlargement for more than two decades and is approved for hair loss in Japan and South Korea. Direction mixed: a proven effect on hair, but off-label in Germany, with a half-life of weeks, sexual side effects and more high-grade prostate tumors in REDUCE.

The score rates the state of knowledge, not the substance. “Safety data 9” means well studied – not harmless. “Track record of use 9” means used long and widely – that is not proof of efficacy.
Subjective assessment by Biohacking Kompakt based on published scoring rules – not a scientific rating and not a medical recommendation. Rules and all ratings (German)

Frequently asked questions about dutasteride

Does dutasteride work better than finasteride against hair loss?