ER-positive breast cancer
First line
Third-generation non-steroidal aromatase inhibitor
ATC code: L02BG03 (Anastrozole)
Brand names
Arimidex, Anastrol, Atrozol
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.
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.
The drug is promoted for these uses outside international guidelines. Each entry below is analyzed against AEMPS, FDA, EMA, Cochrane and major RCTs.
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.
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Absolute contraindication. Teratogen. Immediate discontinuation if pregnancy occurs.
Contraindicated during lactation.
Reference information, not a clinical decision. Discuss feeding pauses or changes with your physician or an IBCLC.
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.
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.
FDA category X. Absolute contraindication. Teratogen. Immediate discontinuation if pregnancy occurs.
Contraindicated during lactation.
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.