What is dutasteride and how does it work?
- What dutasteride is and what it is licensed for in the UK
- How it works and how it differs from finasteride
- What the evidence shows for off-label hair loss use
- How long it takes to produce results
- How to access dutasteride in the UK
What is dutasteride?
Dutasteride is a prescription-only medicine sold under the brand name Avodart, manufactured by GSK, and also available as generic dutasteride. It belongs to the same class of medicines as finasteride: 5-alpha reductase inhibitors.
In the UK, dutasteride is licensed by the MHRA for BPH in adult men only. Its use for male pattern hair loss is off-label and requires a prescriber to assess individual suitability before prescribing.
Good to know
Off-label prescribing is legal in the UK when a registered prescriber determines it is clinically appropriate. Patients should be clearly informed of the off-label status before starting treatment.
How does dutasteride work?
Dutasteride works by inhibiting 5-alpha reductase, the enzyme that converts testosterone into dihydrotestosterone (DHT). DHT causes hair follicles in genetically susceptible men to gradually miniaturise, producing progressively thinner hairs until the follicle becomes dormant.
The key distinction between dutasteride and finasteride is that dutasteride inhibits both type I and type II 5-alpha reductase, whereas finasteride inhibits only type II. This dual inhibition reduces serum DHT by approximately 90-95%, compared to approximately 60-70% with finasteride 1 mg.
| Finasteride 1 mg | Dutasteride 0.5 mg | |
|---|---|---|
| Mechanism | Type II inhibitor only | Dual type I and II inhibitor |
| DHT reduction | Approx. 60–70% | Approx. 90–95% |
| Licensed for hair loss in UK | Yes | No (off-label) |
| Half-life | Approx. 5–6 hours | Approx. 5 weeks |
Dutasteride's significantly longer half-life means it takes longer to clear the body after stopping, which has implications for how long side effects may persist if treatment is discontinued. For a full comparison between the two, see our guide on dutasteride vs. finasteride.
What does the evidence show for dutasteride and hair loss?
While not licensed for hair loss in the UK, dutasteride has a meaningful clinical evidence base for androgenetic alopecia.
A randomised controlled trial found dutasteride 0.5 mg produced significantly greater hair count improvements than finasteride 5 mg at 24 weeks.
Another placebo-controlled trial compared dutasteride 0.5 mg against finasteride 1 mg in 917 men over 24 weeks. Dutasteride produced statistically significantly greater improvements in hair count and patient-assessed hair growth.
The evidence suggests dutasteride produces greater hair retention and regrowth than finasteride. Long-term comparative data and UK regulatory approval for this indication remain limited.
Does topical dutasteride work?
A phase II randomised controlled trial found that topical dutasteride produced significantly greater improvements in hair count than oral finasteride 1 mg over 24 weeks, with modest changes in systemic DHT levels and no adverse events. The low systemic absorption observed in this study supports the rationale that topical dutasteride may offer comparable efficacy to oral treatment with a potentially more favourable side effect profile.
However, topical dutasteride is not MHRA-licensed in any form in the UK, long-term controlled trial data is limited, and it is available only as a specially prepared formulation from some regulated private prescribers. It is a clinically interesting option to discuss with a prescriber rather than an established treatment pathway.
How long does dutasteride take to work for hair loss?
| Timepoint | What typically happens |
|---|---|
| 0–3 months | Possible increased shedding; no visible improvement |
| 3–6 months | Shedding stabilises; early density improvements in some men |
| 6–12 months | Meaningful changes visible; regrowth apparent in responsive patients |
| 12–24 months | Continued improvement; plateau around 24 months |
Good to know
Because of dutasteride's long half-life, it takes longer to fully clear the body after stopping than finasteride. This is an important consideration to discuss with your prescriber before starting.
Who is dutasteride suitable for?
Dutasteride for hair loss may be considered for adult men with androgenetic alopecia where finasteride has not produced sufficient benefit, or where a prescriber determines it appropriate as a first-line off-label option.
Dutasteride is not suitable for women and must not be handled by pregnant women, as it may affect the development of male genitalia in an unborn baby. It is also not suitable for men with severe liver impairment.
How do you access dutasteride in the UK?
Dutasteride is prescription-only and requires a clinical assessment by a UK-registered prescriber. Because its use for hair loss is off-label, the prescriber must assess individual suitability and discuss the off-label status clearly before prescribing.
DoktorABC connects UK patients with licensed prescribers who can assess suitability for dutasteride and issue private prescriptions where clinically appropriate. Always verify that any online service is CQC-registered and uses a GPhC-registered pharmacy at pharmacyregulation.org.
Warning !
Do not purchase dutasteride from unregulated online sources. Report suspected counterfeit products via the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk.
Final thoughts
Dutasteride is a clinically credible option for male pattern hair loss, with evidence suggesting greater efficacy than finasteride due to its dual inhibition mechanism. Its off-label status requires a more considered prescribing conversation than licensed alternatives, but it is a legitimate option for men who have not achieved sufficient results with finasteride or who are exploring treatment with a knowledgeable prescriber.
FAQ
What is dutasteride?
A prescription 5-alpha reductase inhibitor sold as Avodart and in generic form. It is licensed for BPH in the UK; its use for hair loss is off-label.
How does dutasteride work for hair loss?
By inhibiting both type I and type II 5-alpha reductase, reducing DHT by approximately 90-95%, which slows follicle miniaturisation and supports hair retention.
How does dutasteride differ from finasteride?
Dutasteride inhibits both types of 5-alpha reductase; finasteride inhibits only type II. This produces greater DHT reduction and, in clinical trials, greater hair retention and regrowth.
How long does dutasteride take to work?
Visible results are typically apparent at 6-12 months. Some evidence suggests earlier onset than finasteride.
Does topical dutasteride work?
Early evidence is promising but limited. It is not MHRA-licensed and is available only as a specially prepared formulation from some regulated UK private prescribers.
Is dutasteride licensed for hair loss in the UK?
No. It is used off-label. This must be clearly explained by your prescriber before starting treatment.
Where can I report a side effect from dutasteride?
Via the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk, through the Yellow Card app, or by asking your prescriber or pharmacist to report on your behalf.
The DoktorABC medical advisory board
Dr. Roland Ruiken
Medical advisor, Norway
Dr. Viktor Simunovic
Medical advisor, Croatia