[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Aromatase inhibitors](https://durgical.com/en/pharmacology/classes/aromatase-inhibitors/) › Letrozole

[Pharmacology](https://durgical.com/en/pharmacology/) · [Aromatase inhibitors](https://durgical.com/en/pharmacology/classes/aromatase-inhibitors/)

# Letrozole

A tablet that blocks oestrogen production, used for breast cancer after menopause. Like the other aromatase inhibitors, it can weaken the bones.

Updated 2026-11-01

- Class: [Aromatase inhibitors](https://durgical.com/en/pharmacology/classes/aromatase-inhibitors/)
- Enzyme: Aromatase (CYP19A1)
- ATC code: L02BG04
- WHO Model List of Essential Medicines

✂**Aromatase (CYP19A1)**Letrozole

ⓘ No structure with letrozole is available. The figure shows exemestane, another aromatase inhibitor, in the same active site of human aromatase.

**Target in 3D:** Aromatase (CYP19A1). PDB structure 3S7S (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/3S7S) · Drag to rotate · pinch to zoom

## Mechanism of action

Letrozole is a non-steroidal triazole whose nitrogen binds the heme iron of aromatase, reversibly blocking the conversion of androgens into oestrogens. In postmenopausal women this lowers oestrogen in blood and in breast tissue and removes the growth signal of hormone receptor-positive tumours.

- Its triazole ring binds the heme iron of aromatase
- Androgens are no longer converted into oestrogens
- Oestrogen falls in blood and in the tumour
- Hormone receptor-positive cancer cells stop growing

## Pharmacokinetics

**Absorption**
Well absorbed by mouth

**Metabolism**
In the liver, to an inactive metabolite

**Elimination**
Mainly in the urine, as metabolites

**Half-life**
About 2 days; steady state takes weeks

## Indications

- Adjuvant treatment of hormone receptor-positive early breast cancer in postmenopausal women [Breast cancer →](https://durgical.com/en/conditions/breast-cancer/)
- Extended adjuvant treatment after several years of tamoxifen [Breast cancer →](https://durgical.com/en/conditions/breast-cancer/)
- First- and second-line treatment of advanced breast cancer in postmenopausal women [Breast cancer →](https://durgical.com/en/conditions/breast-cancer/)

## Adverse effects

### Common

- Hot flashes
- Joint and muscle pain
- Fatigue, dizziness and somnolence
- Rise in cholesterol
- Sweating

### Serious (rare, important)

- Loss of bone mineral density and fractures
- Fetal harm

## Contraindications

- Pregnancy
- Hypersensitivity to letrozole or any excipient

## Key interactions

**Tamoxifen**
Lowers letrozole blood levels.

**Oestrogen-containing products**
Work against the purpose of treatment.

## What is monitored

- Bone mineral density
- Cholesterol
- Pregnancy status in women who could become pregnant

## Administration and safety

- Oral tablet once a day, with or without food.
- Hazardous drug: avoid handling broken tablets during pregnancy.
- Do not confuse letrozole with anastrozole; they are different products.

## Nursing care

- Confirm that the patient is not pregnant before starting when pregnancy is possible.
- Warn about fatigue, dizziness and sleepiness before driving or using machines.
- Teach about joint pain and hot flashes, and report severe bone pain.
- Support bone health: calcium, vitamin D, exercise and bone density checks.

## Pregnancy and breastfeeding

Contraindicated in pregnancy because it can cause fetal harm; effective contraception is used when pregnancy is possible.

## Memory aid

LETrozole does not LET androgens become oestrogen: the triazole grips the heme iron and holds it.

## Test yourself

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

## Which part of the letrozole molecule binds aromatase?

The nitrogen of its triazole ring, which coordinates the heme iron in the enzyme's active site and blocks it reversibly.

## A patient on letrozole feels drowsy and dizzy. What should she be told?

Fatigue, dizziness and somnolence are known effects; she should be careful when driving or using machines and report them.

## What does extended adjuvant letrozole mean in breast cancer?

Letrozole given to postmenopausal women after they have completed several years of adjuvant tamoxifen, to lower the risk of recurrence further.

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

## Related drugs

- [Anastrozole](https://durgical.com/en/pharmacology/anastrozole/)
- [Exemestane](https://durgical.com/en/pharmacology/exemestane/)
- [Tamoxifen](https://durgical.com/en/pharmacology/tamoxifen/)

## Related conditions

- [Breast cancer](https://durgical.com/en/conditions/breast-cancer/)

[← Back to the class: Aromatase inhibitors](https://durgical.com/en/pharmacology/classes/aromatase-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: [Letrozole: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a698004.html) (MedlinePlus (U.S. National Library of Medicine), 2018); [DailyMed - LETROZOLE tablet, film coated](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=8ebda73d-82a3-4b17-8a81-a1f258003d32) (DailyMed (U.S. National Library of Medicine), 2025); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=L02BG04) (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

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Source: https://durgical.com/en/pharmacology/letrozole/
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