Dutasteride

5-α-reductase inhibitors
5-α-reductase inhibitors
Pregnancy: contraindicated
Contraindicated: it can disturb male fetal genital development, and because it lingers in the body men wait before donating blood.

An oral inhibitor of both 5-α-reductase types, used in benign prostatic hyperplasia. It stays in the body for months after the last capsule.

Updated Nov 1, 2026

Quick facts

Group: 5-α-reductase inhibitors
Target: Steroid 5-α-reductase types 1 and 2 (SRD5A1 and SRD5A2)
Used for: Reduction of the risk
Key effects: Erectile dysfunction · Decreased libido
Monitor: PSA · Urinary symptoms · Breast changes
ATC: G04CB02

No doses: the clinician sets them by the current guideline.

Mechanism of action

Steroid 5-α-reductase types 1 and 2 (SRD5A1 and SRD5A2)Dutasteride

No dutasteride-bound structure is available; the figure shows human 5-α-reductase type 2 with finasteride, a related azasteroid that occupies the same active site, joined to NADPH.

Target in 3D: Steroid 5-α-reductase types 1 and 2 (SRD5A1 and SRD5A2). PDB structure 7BW1 (RCSB PDB, public domain). View the structure at RCSB PDB

Dutasteride inhibits both 5-α-reductase type 1 and type 2, so it lowers dihydrotestosterone (DHT) more completely than finasteride. With less DHT the prostate shrinks over months, urinary symptoms improve and the risk of acute retention and surgery falls.

Dutasteride blocks 5-α-reductase types 1 and 2
Conversion of testosterone to DHT almost stops
Androgen-driven prostate growth reverses over months
Symptoms improve and the risk of retention falls

Indications

Symptomatic benign prostatic hyperplasia with an enlarged prostate, alone or with tamsulosin Benign prostatic hyperplasia →
Reduction of the risk of acute urinary retention and BPH surgery Benign prostatic hyperplasia →

Adverse effects

Common

Erectile dysfunction
Decreased libido
Ejaculation disorders
Breast enlargement or tenderness

Contraindications

Pregnancy (and women who may become pregnant)
Previous significant reaction to dutasteride or another 5-α-reductase inhibitor
Not indicated in women or children

Key interactions

Potent, long-term CYP3A4 inhibitors (ritonavir): Higher dutasteride levels; used with caution
Tamsulosin: Intended combination for faster relief and less progression

What is monitored

PSA: a new baseline about three months after starting; confirmed rises are investigated
Urinary symptoms
Breast changes
Signs of allergy

Administration and safety

Capsules are swallowed whole, not chewed or opened; the contents irritate the mouth and throat
With or without food
Women who are or may be pregnant do not handle the capsules, especially leaking ones; contact is washed off with soap and water
Men do not donate blood until six months after the last dose

Pregnancy and breastfeeding

Contraindicated: it can disturb male fetal genital development, and because it lingers in the body men wait before donating blood.

Nursing care

Teach to swallow the capsule whole
Teach household precautions for pregnant women
Explain the blood-donation deferral after stopping
Tell lab staff about the drug when PSA is measured
Ask about sexual side effects and report breast changes

Pharmacokinetics

Absorption: Oral, with or without food
Metabolism: In the liver by CYP3A4 and CYP3A5
Half-life: About five weeks at steady state; still detectable four to six months after stopping
Onset and duration: Symptoms may start to improve after about three months

Test yourself

Think of the answer, then tap the question to see it.

How does dutasteride differ from finasteride at the enzyme level?

Dutasteride inhibits both 5-α-reductase type 1 and type 2; finasteride inhibits mainly type 2.

Why may a man on dutasteride not donate blood for six months after the last dose?

It has a very long half-life and could reach a pregnant woman through transfused blood, with risk to a male fetus.

Why must dutasteride capsules not be opened?

The contents irritate the mouth and throat, and leaking capsules expose others (especially pregnant women) to the drug.

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Connections

← Back to the class: 5-α-reductase inhibitors

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: DailyMed - DUTASTERIDE capsule (DailyMed (U.S. National Library of Medicine), 2026); Dutasteride: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

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Representative model, for educational purposes only.