Pharmacology · 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
No structure with letrozole is available. The figure shows exemestane, another aromatase inhibitor, in the same active site of human aromatase.
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 →
- Extended adjuvant treatment after several years of tamoxifen Breast cancer →
- First- and second-line treatment of advanced breast cancer in postmenopausal women Breast cancer →
Adverse effects
Common
- Hot flashes
- Joint and muscle pain
- Fatigue, dizziness and somnolence
- Rise in cholesterol
- Sweating
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.
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.
Related drugs
Related conditions
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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 (MedlinePlus (U.S. National Library of Medicine), 2018); DailyMed - LETROZOLE tablet, film coated (DailyMed (U.S. National Library of Medicine), 2025); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).
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Representative model, for educational purposes only.