Medication questions Dutasteride
Finasteride vs dutasteride: what are the differences?
Short answer
Both lower DHT by blocking 5-alpha-reductase, but they differ in fact. Finasteride blocks the type II enzyme and is licensed in the UK for male pattern hair loss. Dutasteride blocks types I and II and is licensed only for an enlarged prostate, so its use for hair loss is off-label. It also stays in the body for weeks. Which, if either, suits you is an individual clinical decision.
Key facts
- Enzymes: finasteride blocks type II; dutasteride blocks types I and II.
- Licence: finasteride 1 mg for male pattern hair loss; dutasteride for enlarged prostate only.
- Half-life: finasteride about 5 to 6 hours; dutasteride about 3 to 5 weeks.
- Blood donation deferral: 4 weeks for finasteride, 6 months for dutasteride.
- MHRA: finasteride warnings 2024 and 2026; precautionary dutasteride warning 2026.
How each one works
Both are 5-alpha-reductase inhibitors. They block 5-alpha-reductase, the enzyme that converts testosterone into DHT, the hormone involved in male pattern hair loss. The enzyme comes in two main forms:
Finasteride is "a competitive and specific inhibitor of type II 5α-reductase" (Propecia SmPC).
Dutasteride works by "inhibiting both type 1 and type 2, 5α-reductase isoenzymes" (Avodart SmPC).
That is a difference in mechanism. It does not tell you which, if either, will suit you.
Licensing
Finasteride 1 mg (Propecia and generics) is licensed in the UK to treat male pattern hair loss in men.
Dutasteride 0.5 mg (Avodart and generics) is licensed in the UK for the "treatment of moderate to severe symptoms of benign prostatic hyperplasia", an enlarged prostate. Its effect on hair was not formally studied during the trials for its licence. Prescribing it for hair loss is off-label, and the prescriber must explain this before you start. Our page on whether dutasteride is licensed for hair loss covers what that means.
Half-life, form and handling
Half-life (the time for the level in the blood to fall by half): finasteride about 5 to 6 hours in men aged 18 to 60; dutasteride about 3 to 5 weeks. So dutasteride takes months, not days, to leave the body, which affects how quickly any side effect may ease after stopping.
Form: finasteride is a film-coated tablet; dutasteride is a soft capsule that should be swallowed whole and not chewed or opened, because the contents can make the mouth or throat sore.
Handling in pregnancy: women who are or may be pregnant should not handle crushed or broken finasteride tablets, or leaking dutasteride capsules, which can be absorbed through the skin.
Semen: the Avodart leaflet says to use a condom because dutasteride is found in semen and must not reach a partner who is or may be pregnant. For finasteride, the NHS says manufacturers recommend a condom but the actual risk is unlikely to be significant.
MHRA warnings, PSA and blood donation
MHRA warnings. Finasteride is the subject of Drug Safety Updates on 29 April 2024 and 11 May 2026, covering depression, suicidal thoughts and sexual side effects that may persist after stopping, with a patient alert card in every pack. The 11 May 2026 update added a precautionary warning for dutasteride because mood changes have been reported with finasteride, noting that "the data for dutasteride was very limited". The Avodart SmPC says sexual side effects may persist after stopping, and that dutasteride's role in this is unknown. See MHRA safety updates.
PSA tests. Both lower PSA. For finasteride 1 mg, the SmPC says doubling the PSA result should be considered. For dutasteride, PSA falls by about 50% after 6 months.
Blood donation. UK donor guidelines say no donating within 4 weeks of finasteride or 6 months of dutasteride. See finasteride and blood donation.
Choosing between them
There is no general answer to "which is better", and we do not make that comparison. The right choice depends on your hair loss, your health, your plans and how you weigh licensing, half-life and side-effect warnings. At WMG Meds, a doctor may consider dutasteride where finasteride has not given an adequate response, after explaining the off-label use. Choosing neither is also valid.
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Is dutasteride stronger than finasteride?
We do not make comparisons of strength or effectiveness between prescription medicines. The factual differences are that dutasteride blocks both types of 5-alpha-reductase, stays in the body much longer, and is not licensed for hair loss in the UK. How either works for you can only be judged by a prescriber and over time.
Do finasteride and dutasteride have the same side effects?
They overlap. Both list reduced sex drive, erection problems and ejaculation problems, which may continue after stopping, plus breast tenderness or enlargement. The MHRA warns about depression and suicidal thoughts with finasteride, and added a precautionary mood warning for dutasteride in 2026.
Can I switch from finasteride to dutasteride?
It is a prescribing decision. A doctor may consider dutasteride, off-label, where finasteride has not given an adequate response. They should explain the off-label use, the long half-life and the side-effect warnings before you decide.
Which one leaves the body faster?
Finasteride. Its half-life is about 5 to 6 hours, against about 3 to 5 weeks for dutasteride. That is why the blood donation deferral is 4 weeks for finasteride and 6 months for dutasteride.
Can women take either?
No. Both are contraindicated in women under their UK product information, and pregnant women should not handle crushed finasteride tablets or leaking dutasteride capsules. See can women take finasteride.
Sources
- Propecia 1 mg: summary of product characteristics (eMC, revised 29 June 2026)
- Avodart 0.5 mg soft capsules: summary of product characteristics (eMC, revised 11 August 2026)
- Avodart 0.5 mg soft capsules: patient information leaflet (eMC, revised March 2026)
- MHRA Drug Safety Update, 11 May 2026: Finasteride and dutasteride, updated safety warnings
- JPAC, Guidelines for the UK Blood Transfusion Services: Anti-androgens (whole blood, September 2026)
Facts checked against these sources on 4 October 2026. This page is general information, not personal medical advice. Read our editorial policy.