Aromatase inhibitor (non-steroidal) Pregnancy: Contraindicated during pregnancy and breastfeeding. No human data; animal studies have shown reproductive toxicity.

Anastrozole

Brand names: Arimidex

Anastrozole is a non-steroidal aromatase inhibitor used in postmenopausal women for hormone-receptor-positive early and advanced breast cancer, and for adjuvant treatment and risk reduction. It is ineffective in premenopausal women unless ovarian function is suppressed.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: 1 mg (one tablet)

Route: Oral

Frequency: Once a day

Recommended dose for adults including the elderly is one 1 mg tablet once a day. For postmenopausal women with hormone receptor-positive early invasive breast cancer, the recommended duration of adjuvant endocrine treatment is 5 years. For primary prevention of breast cancer in postmenopausal women at moderate or high risk, treatment duration is 5 years (initiated only by a practitioner experienced in this indication, within a shared care pathway; benefit-risk and breast cancer risk assessment essential first). No dose change with mild/moderate renal impairment or mild hepatic disease; caution in severe renal impairment and in moderate-to-severe hepatic impairment.

Dose adjustments

Renal

No dose change in mild or moderate renal impairment; in severe renal impairment administer with caution (exposure not increased).

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

US labelling (FDA)

Reference — US labelling, may differ from UK

One 1 mg tablet taken once daily ( 2.1 ) 2.1 Recommended Dose The dose of anastrozole tablet is one 1 mg tablet taken once a day. For patients with advanced breast cancer, anastrozole tablets should be continued until tumor progression. Anastrozole tablets can be taken with or without food. For adjuvant treatment of early breast cancer in postmenopausal women, the optimal duration of therapy is unknown. In the ATAC trial, anastrozole was administered for five years [see Clinical Studies ( 14.1 )]. No dosage adjustment is necessary for patients with renal impairment or for elderly patients [see Use in Specific Populations ( 8.6 )]. 2.2 Patients with Hepatic Impairment No changes in dose are …

Source: US FDA prescribing information (openFDA / DailyMed), label dated 2026-02-11. Accessed 2026-06-12. US dosing and indications can differ from UK practice — use UK sources for prescribing decisions.

Contraindications

Pregnant or breastfeeding women
Known hypersensitivity to anastrozole or to any of the excipients

Side effects

Headache (very common)
Hot flushes (very common)
Nausea (very common)
Rash (very common)
Arthralgia/joint stiffness, arthritis, osteoporosis, asthenia (very common)

Interactions

Tamoxifen — co-administration should be avoided; may diminish anastrozole's pharmacological action (and reduced anastrozole plasma concentration by 27%)
Estrogen-containing therapies — should be avoided; may diminish anastrozole's pharmacological action
LHRH analogues — no data to support use of anastrozole with LHRH analogues

Clinical monograph

How it works

It reversibly inhibits the aromatase enzyme, blocking the peripheral conversion of androgens to oestrogen; in postmenopausal women, where the ovaries no longer produce oestrogen, this markedly lowers circulating oestrogen and deprives hormone-sensitive tumours of stimulation.

Prescribing in practice

It accelerates bone loss and the risk of osteoporosis and fractures, so assess bone mineral density before and during treatment and ensure adequate calcium and vitamin D, with bone-protective therapy where indicated.
It commonly causes arthralgia and other musculoskeletal symptoms and hot flushes, and can raise cholesterol — review lipids and manage symptoms to support adherence.
It is ineffective in premenopausal women and contraindicated in pregnancy and breastfeeding; confirm postmenopausal status (or effective ovarian suppression) before use.

Monitoring

Assess bone mineral density at baseline and periodically, and monitor lipids; review tolerability of joint and vasomotor symptoms at follow-up.

Counselling the patient

Joint aches and stiffness and hot flushes are common; report them, as support and adjustments can help you continue treatment.
Looking after your bones matters — take calcium and vitamin D as advised and keep weight-bearing activity up.
Report unusual bone pain, or any new lump or symptom, to your team.

Evidence & guidelines

Aromatase inhibitors are a standard endocrine therapy for hormone-receptor-positive breast cancer in postmenopausal women (e.g. the ATAC trial), recommended within NICE breast-cancer guidance.

Reference: SmPC Arimidex; ATAC trial Lancet 2002; 359:2131-39; MA.17R NEJM 2016; IBIS-II Lancet 2014; 383:1041-48; NICE NG101 (Early breast cancer); ESMO Breast Cancer Guidelines 2024; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways