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Anastrozole

AEMPS

Third-generation non-steroidal aromatase inhibitor

ATC code: L02BG03

Brand names: Arimidex, Anastrol, Atrozol

Updated · Methodology

Indications

A

ER-positive breast cancer

First line

First-line adjuvant endocrine therapy for hormone-receptor positive breast cancer in postmenopausal women per ESMO 2024 and NCCN 2024. Dose 1 mg once daily for 5–10 years. The ATAC trial showed superiority over tamoxifen in disease-free survival. Also used as first-line for metastatic disease in postmenopausal women combined with a CDK4/6 inhibitor.

Postmenopausal women only.

Sources

  1. AEMPS: Ficha técnica de Anastrozol (2024)
  2. Lancet: Aromatase inhibitors versus tamoxifen in early breast cancer: patient-level meta-analysis of the randomised trials. (2015)
  3. Lancet Oncol: Effect of anastrozole and tamoxifen as adjuvant treatment for early-stage breast cancer: 10-year analysis of the ATAC trial. (2010)

ICD-10: C50 · ICD-11: 2C6Z

Marketing claims without evidence base

The drug is promoted for these uses outside international guidelines. Each entry below is analyzed against AEMPS, FDA, EMA, Cochrane and major RCTs.

F

Athletic endurance

Not recommended

Anastrozole is used by amateur bodybuilders and self-administered AAS users for suppressing testosterone-to-estrogen aromatization. ASCO 2022 and the AEMPS Ficha Técnica confine anastrozole to hormone-receptor-positive breast cancer in postmenopausal women. Approved indications in men or athletes do not exist. Use causes marked bone mineral density loss ( Drug Safety Communication 2010), arthralgia, dyslipidemia and cardiovascular risk.

Sources

  1. AEMPS: Ficha técnica de Anastrozol (2024)
  2. ISSN: International Society of Sports Nutrition position stand: creatine supplementation (2017)
How to read tiers A–F
  • AStrong evidence – first or second line in international guidelines
  • BRecommended in selected cases
  • CStudy data contradict each other
  • DBenefit not proven, no documented harm
  • FDocumented harm, or risk without benefit

Mechanism of action

A selective reversible aromatase inhibitor – the cytochrome P450 enzyme converting androgens to estrogens in peripheral tissues. In postmenopausal women, lowers estradiol by 80–90%. Efficacy comparable to letrozole and exemestane – all three third-generation aromatase inhibitors are roughly equivalent. Does not affect cortisol or aldosterone synthesis. Half-life 50 hours; once-daily dosing.

Safety

Contraindications

  • Anastrozole hypersensitivity
  • Premenopausal status without ovarian suppression
  • Pregnancy and lactation
  • Severe renal or hepatic impairment

Serious adverse effects

  • Osteoporosis and fractures
  • Hyperlipidemia
  • Cardiovascular events (higher risk than with tamoxifen)
  • Hepatotoxicity
  • Severe cutaneous reactions

Common adverse effects

  • Hot flashes and night sweats
  • Joint and muscle pain
  • Fatigue
  • Nausea
  • Reduced libido and vaginal dryness
  • Dry skin

Pregnancy: can you take Anastrozole?

Absolute contraindication. Teratogen. Immediate discontinuation if pregnancy occurs.

Breastfeeding: can you take Anastrozole?

Contraindicated during lactation.

Calculate RIDFull profile on NIH LactMed ↗

Reference information, not a clinical decision. Discuss feeding pauses or changes with your physician or an IBCLC.

Practical notes

Timing and administration

Take once daily, with or without food. Standard adjuvant duration is 5 years; up to 10 years at high recurrence risk. Pre-treatment and 12-month DXA. All patients receive calcium 1000–1200 mg and vitamin D 800–1000 IU/day; in osteoporosis or high risk, bisphosphonates or denosumab. Regular lipid profile monitoring.
Label mentions6 mentions

Verbatim lines from the interaction sections, in the language of the label

From this drug’s label

  • CriticalTamoxifen
    «DRUG INTERACTIONS: Tamoxifen: Do not use in combination with anastrozole tablets. No additional benefit seen over tamoxifen monotherapy ( 7.1 , 14.1 )»

    FDA, section 7 · Open on DailyMed

  • MajorTamoxifen
    «Debe evitarse la co-administración de tamoxifeno o terapias que incluyan estrógeno con anastrozol, ya que esto puede disminuir su acción farmacológica (ver sección 4.4 y 5.1).»

    AEMPS, section 4.5 · Open on CIMA

  • anticoagulantsclass named in the label
    «Warfarin: In a study conducted in 16 male volunteers, anastrozole did not alter the exposure (as measured by C max and AUC) and anticoagulant activity (as measured by prothrombin time, activated…»

    FDA, section 7 · Open on DailyMed

  • Warfarin
    «El anastrozol inhibe los CYPs 1A2, 2C8/9 y 3A4 in vitro . Estudios clínicos con antipirina y warfarina mostraron que el anastrozol a una dosis de 1 mg no inhibió significativamente el metabolismo de…»

    AEMPS, section 4.5 · Open on CIMA

  • Warfarin
    «Warfarin: In a study conducted in 16 male volunteers, anastrozole did not alter the exposure (as measured by C max and AUC) and anticoagulant activity (as measured by prothrombin time, activated…»

    FDA, section 7 · Open on DailyMed

From other drugs’ labels

  • Tamoxifen
    «Drug Interactions:: Based on clinical and pharmacokinetic results from the anastrozole adjuvant trial, tamoxifen citrate should not be administered with anastrozole (see CLINICAL PHARMACOLOGY – Drug-…»

    FDA, section 7 · Open on DailyMed

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Frequently asked

What is Anastrozole used for?

Anastrozole is evaluated for the following indications with varying evidence strength: ER-positive breast cancer (evidence tier A), Athletic endurance (evidence tier F). See the full indication matrix with dosing and citations above on this page.

What are the side effects of Anastrozole?

Common side effects of Anastrozole (≥ 1 in 100): Hot flashes and night sweats, Joint and muscle pain, Fatigue, Nausea, Reduced libido and vaginal dryness, Dry skin. See the Safety section for uncommon and serious reactions.

Is Anastrozole safe during pregnancy?

Absolute contraindication. Teratogen. Immediate discontinuation if pregnancy occurs.

Is Anastrozole compatible with breastfeeding?

Contraindicated during lactation.

Who should not take Anastrozole?

Anastrozole is contraindicated in: Anastrozole hypersensitivity; Premenopausal status without ovarian suppression; Pregnancy and lactation; Severe renal or hepatic impairment. Full list in the Safety section.

Official sources

Direct links to regulator labels. Open in a new tab.

Other drugs in this group

Abiraterone, Bicalutamide, Exemestane, Letrozole, Tamoxifen