[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [5-α-reductase inhibitors](https://durgical.com/en/pharmacology/classes/5-reductase-inhibitors/) › Dutasteride

# 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](https://durgical.com/en/pharmacology/classes/5-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.

On this page

- The basics Mechanism of action
- Indications
- Adverse effects
- Pharmacokinetics
- Memory aid

- Clinical What the labels mean

- Safety Contraindications
- Key interactions
- What is monitored
- Administration and safety
- Pregnancy and breastfeeding
- Nursing care

- Study Test yourself

- Connections Connections

## 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](https://www.rcsb.org/structure/7BW1) · Drag to rotate · pinch to zoom

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 →](https://durgical.com/en/conditions/benign-prostatic-hyperplasia/)
- Reduction of the risk of acute urinary retention and BPH surgery [Benign prostatic hyperplasia →](https://durgical.com/en/conditions/benign-prostatic-hyperplasia/)

## Adverse effects

### Common

- Erectile dysfunction
- Decreased libido
- Ejaculation disorders
- Breast enlargement or tenderness

### Serious (rare, important)

- High-grade prostate cancer (increase with long use)
- Breast lumps or nipple discharge
- Severe allergic reactions, including angioedema and skin peeling
- Lower sperm count, semen volume and motility

## 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

## Memory aid

DUtasteride = «DUal and DUrable»: both enzymes, five-week half-life, six months before giving blood.

## 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.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/dutasteride/)

[More Pharmacology questions →](https://durgical.com/en/practice/?f=pharmacology)

## What the labels mean

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

## Connections

## Related drugs 2

- [Finasteride](https://durgical.com/en/pharmacology/finasteride/)
- [Tamsulosin](https://durgical.com/en/pharmacology/tamsulosin/)

## Related conditions 1

- [Benign prostatic hyperplasia](https://durgical.com/en/conditions/benign-prostatic-hyperplasia/)

[← Back to the class: 5-α-reductase inhibitors](https://durgical.com/en/pharmacology/classes/5-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](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=e537c60d-9ba2-4e7f-a405-2b915dcd7ead) (DailyMed (U.S. National Library of Medicine), 2026); [Dutasteride: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a603001.html) (MedlinePlus (U.S. National Library of Medicine), 2026); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=G04CB02) (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/dutasteride/