5-alpha reductase inhibitor (Type I and II) Pregnancy: Contraindicated for use by women. Dutasteride may, if administered to a woman carrying a male foetus, inhibit development of the external genitalia; small amounts are recovered in semen, so when the patient's partner is or may potentially be pregnant he should avoid exposing her to semen by using a condom (risk greatest in the first 16 weeks of pregnancy).

Dutasteride

Brand names: Avodart, Combodart (with tamsulosin)

Dutasteride is a 5-alpha-reductase inhibitor used for benign prostatic hyperplasia (BPH) to relieve symptoms, reduce the risk of acute urinary retention and the need for surgery. It provides dual inhibition of both type 1 and type 2 5-alpha-reductase.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: 0.5 mg (one capsule) once a day

Route: Oral (soft capsule — swallow whole, do not chew or open; with or without food)

Frequency: Once daily

§4.2: adults including the elderly — one 0.5 mg capsule once a day; no dose adjustment in the elderly. May be administered alone or in combination with the alpha-blocker tamsulosin 0.4 mg (combination therapy should be prescribed after careful benefit–risk assessment because of the potential increased risk of adverse events including cardiac failure, §4.4). Although an improvement may be observed at an early stage, it can take up to 6 months before a response to treatment is achieved. Contact with capsule contents may irritate the oropharyngeal mucosa. Hepatic impairment: effect not studied — caution in mild to moderate impairment; contraindicated in severe hepatic impairment. Paediatric: contraindicated in children and adolescents (no per-kg regimen — paedDose null). §4.4: dutasteride reduces mean serum PSA by approximately 50% after 6 months; establish a new PSA baseline at 6 months and monitor thereafter.

Dose adjustments

Renal

The effect of renal impairment on dutasteride pharmacokinetics has not been studied; no adjustment in dosage is anticipated for patients with renal impairment.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

US labelling (FDA)

Reference — US labelling, may differ from UK

The recommended dosage of dutasteride and tamsulosin hydrochloride capsules is 1 capsule (0.5 mg dutasteride and 0.4 mg tamsulosin hydrochloride) taken once daily approximately 30 minutes after the same meal each day. The capsules should be swallowed whole and not chewed or opened. Contact with the contents of the dutasteride and tamsulosin hydrochloride capsule may result in irritation of the oropharyngeal mucosa. Take one capsule daily approximately 30 minutes after the same meal each day. ( 2 ) Swallow capsule whole. ( 2 )

Source: US FDA prescribing information (openFDA / DailyMed), label dated 2026-01-13. Accessed 2026-06-12. US dosing and indications can differ from UK practice — use UK sources for prescribing decisions.

Contraindications

Women, and children and adolescents
Hypersensitivity to dutasteride, other 5-alpha reductase inhibitors, soya, peanut or any of the other excipients
Severe hepatic impairment

Side effects

Impotence (6.0% in year 1)
Decreased libido (3.7% in year 1)
Ejaculation disorders, including decreased semen volume (1.8% in year 1)
Breast disorders — breast tenderness and enlargement (1.3%)
Allergic reactions including rash, pruritus, urticaria, localised oedema and angioedema
Alopecia (primarily body hair loss) and hypertrichosis (uncommon)

Interactions

US label §7 (no §4.5 content in the fetched UK SPC extract): potent chronic CYP3A4 inhibitors (e.g. ritonavir) — use with caution; dutasteride is extensively metabolised by CYP3A4/CYP3A5
US label §7: verapamil or diltiazem decrease dutasteride clearance and increase exposure — the change is not considered clinically significant and no dose adjustment is recommended
US label §7: alpha-adrenergic antagonists (tamsulosin, terazosin) — no effect on the steady-state pharmacokinetics of either alpha-blocker
US label §7: cholestyramine (12 g given 1 hour after a 5 mg dose) does not affect the relative bioavailability of dutasteride

Clinical monograph

How it works

It inhibits 5-alpha-reductase, reducing conversion of testosterone to dihydrotestosterone (DHT). Lower DHT leads to gradual shrinkage of the prostate over months.

Prescribing in practice

Pregnant women, or those who may become pregnant, must not handle leaking capsules because absorbed drug may harm a developing male fetus; the capsules should be swallowed whole and not opened.
It roughly halves serum PSA, so the PSA result must be interpreted accordingly (a doubling gives an approximate true value), and any confirmed rise in PSA during treatment should be evaluated.
Sexual dysfunction (reduced libido, erectile or ejaculatory problems), gynaecomastia and mood changes including depression can occur; men should not donate blood during treatment and for a period after stopping.

Monitoring

Establish a baseline PSA, re-establish a new baseline after treatment is established, and assess any subsequent rise; symptomatic response develops gradually over months. Review for sexual, breast and mood adverse effects, and reassess continued need over time.

Counselling the patient

Swallow the capsules whole; pregnant women or those who could become pregnant must not handle leaking capsules.
This medicine lowers the PSA blood test, which is taken into account when interpreting prostate results.
Do not donate blood during treatment and for the advised period afterwards, and tell us about any reduced sex drive, breast changes or low mood.

Evidence & guidelines

5-alpha-reductase inhibitors are guideline-recommended for BPH, particularly with larger prostates (NICE NG97).

Reference: NICE NG118; EAU BPH Guidelines; CombAT Trial; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways