Dutasteride
Dutasteride is a dual 5α-reductase inhibitor that blocks both type 1 and type 2 isoenzymes, reducing dihydrotestosterone (DHT) more completely than finasteride. It is used for benign prostatic hyperplasia and off-label for androgenetic alopecia.
- Chemical formula
- C27H30F6N2O2
- CAS number
- 164656-23-9
- ATC code
- G04CB02
- Molecular weight
- 528.53 g/mol
- Drug class
- Dual 5α-reductase inhibitor (type 1 and type 2)
- Also known as
- Avodart, GG745
What is it?
Dutasteride is a 5α-reductase inhibitor approved in 2001 for the treatment of symptomatic benign prostatic hyperplasia (BPH). Unlike finasteride, which selectively inhibits the type 2 isoenzyme, dutasteride inhibits both type 1 and type 2 isoenzymes, reducing serum DHT levels by approximately 90% (vs ~70% with finasteride). The originator brand is Avodart (GlaxoSmithKline) with authorised generic dutasteride widely available.
Mechanism of action
Dutasteride irreversibly inhibits both isoenzymes of 5α-reductase, the enzyme that converts testosterone to dihydrotestosterone (DHT). The dual blockade results in more complete suppression of circulating DHT than achievable with type-2-selective agents. In the prostate, reduced DHT shrinks gland volume over months and improves obstructive urinary symptoms. In the scalp, the same mechanism slows or reverses androgen-driven hair miniaturisation in androgenetic alopecia.
Pharmacokinetics
Dutasteride is highly lipophilic and accumulates extensively in tissue. After oral administration, it is well absorbed and undergoes CYP3A4 hepatic metabolism. The terminal half-life is exceptionally long — approximately 5 weeks — which means dutasteride persists in the body for months after the last dose. Steady state is reached over 6 months of daily dosing. Excretion is primarily faecal.
Indications
Dutasteride is approved for symptomatic benign prostatic hyperplasia, alone or in combination with tamsulosin (Combodart/Jalyn) for greater symptom relief. It is not formally approved in most regions for male pattern hair loss but is used off-label, sometimes in cases where finasteride has been ineffective. It is contraindicated in women, particularly those who could become pregnant, due to teratogenic risk to a male fetus.
Safety profile
Common adverse effects include sexual side effects (decreased libido, erectile dysfunction, ejaculatory disorders), gynaecomastia and breast tenderness. Some adverse effects can persist for months after stopping due to the long half-life. The PSA level is approximately halved during dutasteride therapy, which complicates prostate cancer screening — this is a recognised effect that the prescriber and laboratory account for. Pregnant women should not handle broken capsules due to teratogenicity.
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Frequently asked questions
How is dutasteride different from finasteride? ▾
Both are 5α-reductase inhibitors, but dutasteride blocks both type 1 and type 2 isoenzymes while finasteride only blocks type 2. Dutasteride reduces DHT more completely (~90% vs ~70%) and has a much longer half-life (~5 weeks vs ~6 hours). For BPH and likely for hair loss, dutasteride may be slightly more effective but with longer-persisting side effects.
Can women take dutasteride? ▾
Dutasteride is contraindicated in women, particularly women who could become pregnant, because it can cross the placenta and cause feminisation of a male fetus. Women should not handle broken or leaking dutasteride capsules. According to the prescribing information, dutasteride is exclusively for adult male use.
Why does dutasteride affect PSA? ▾
Dutasteride lowers serum PSA by approximately 50% over six months of treatment. This is a known pharmacological effect of 5α-reductase inhibition and not a sign of reduced prostate cancer risk. According to current urology guidelines, PSA values during dutasteride therapy should be doubled mentally to compare with off-treatment baselines for screening purposes.
The information on this website is provided for reference and educational purposes only. It does not replace consultation with a qualified healthcare professional.