Anastrozole

Anastrozole is a prescription tablet that lowers oestrogen levels by blocking the aromatase enzyme. It is approved to treat hormone receptor-positive breast cancer in women after the menopause.

What it is

Anastrozole is a tablet medicine from the group called aromatase inhibitors. It is sold under the brand name Arimidex and as generic versions ^[1]. It is used in the treatment of breast cancer in women who have been through the menopause ^[1]. It is a prescription-only medicine and is used under the care of a cancer specialist.

How it works

Aromatase is the enzyme that turns androgens (such as testosterone) into oestrogens. Anastrozole is a selective, non-steroidal aromatase inhibitor, so it lowers the amount of oestrogen in the body ^[1]. In postmenopausal women it reduced blood oestradiol by about 70% within 24 hours and by about 80% after two weeks of treatment ^[1]. Its average elimination half-life is about 50 hours ^[1].

Approved medical uses

• Adjuvant treatment of hormone receptor-positive early breast cancer in postmenopausal women ^[1].
• Advanced breast cancer in postmenopausal women, as a first-line or second-line treatment ^[1].
• It is not approved for men and must not be used by women who have not been through the menopause, in whom it offers no benefit ^[1].

What the research shows

• Breast cancer trials in women. In an early breast cancer trial summarised in the US label, anastrozole was compared with tamoxifen. Women with pre-existing ischaemic heart disease had more ischaemic cardiovascular events on anastrozole (17%) than on tamoxifen (10%) ^[1].
• Children. Anastrozole has been studied in pubertal boys with gynaecomastia (breast tissue growth) and in girls with McCune-Albright syndrome. The label states that effectiveness was not shown in either group ^[1].
• Men with low testosterone or infertility. Aromatase inhibitors block the conversion of testosterone to oestrogen, and may counteract the way oestrogen and testosterone suppress the hormones that drive the testes ^[2]. The American Urological Association (AUA) says clinicians may use aromatase inhibitors, selective oestrogen receptor modulators or hCG in men with testosterone deficiency who want to keep their fertility. This is a conditional recommendation based on lower-quality evidence, and it is an off-label use ^[3].
• Limits of the evidence in men. Reviewers describe these fertility approaches as not well established, limited in how widely they apply, and carrying side effects ^[2]. The bone and cholesterol effects described below come from studies in women with breast cancer ^[1].

Known risks and side effects

• Bone thinning: anastrozole can reduce bone mineral density, which may lead to osteoporosis and fractures ^[1].
• Cholesterol: total cholesterol may rise during treatment ^[1].
• Heart disease: in women with existing ischaemic heart disease, ischaemic cardiovascular events were more common than with tamoxifen ^[1].
• Common effects include hot flushes, weakness, joint pain, arthritis, back pain, high blood pressure, low mood, nausea and vomiting, rash, sleep problems and headache ^[1].
• Not for premenopausal women or for use in pregnancy ^[1].
• Sport: anastrozole is prohibited at all times under the World Anti-Doping Agency (WADA) Prohibited List ^[4].

Blood tests commonly monitored

• Cholesterol (lipid profile): the label advises monitoring during treatment because cholesterol may rise ^[1].
• Bone mineral density: not a blood test, but bone density scans are recommended during treatment because of the risk of bone loss ^[1].
• Oestradiol and testosterone: aromatase inhibitors act by changing the balance between these hormones, so they are the main measures discussed in reviews of their use in men ^[2]. There are no official monitoring guidelines for anastrozole in men because it is not approved for use in men ^[1].

Sources

1. US Food and Drug Administration. Arimidex (anastrozole) tablets label. FDA, 2014. accessdata.fda.gov
2. Herati AS, Kohn TP, Kassiri B. New frontiers in fertility preservation: a hypothesis on fertility optimization in men with hypergonadotrophic hypogonadism. Translational Andrology and Urology, 2020. PMC
3. American Urological Association (Mulhall, et al.). Evaluation and Management of Testosterone Deficiency: AUA Guideline. Journal of Urology and auanet.org, 2018 (validity confirmed 2024). auanet.org
4. World Anti-Doping Agency. World Anti-Doping Code International Standard: Prohibited List 2026. WADA, 2025. Prohibited List 2026 (PDF copy hosted by CONMEBOL)

Related

Last reviewed 7 October 2026. General information, not medical advice. Found a mistake? Email [email protected].