5-alpha reductase inhibitor (Type I and II)

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.

Dosing — being independently re-sourced

ClinCalc Pro is rebuilding its dose data from primary open sources — the manufacturer SmPC (eMC), the WHO Model Formulary and other official references — under clinician review. This drug's structured dose is not yet published here. Confirm all doses 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.

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. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways