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Anastrozole (Arimidex) is a prescription aromatase inhibitor used to treat hormone receptor-positive breast cancer in postmenopausal women, taken as one 1 mg tablet daily.
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Dr. Steve Malen, PharmD
Dr. Steven Blikstein, PharmD
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Anastrozole (Arimidex) is a nonsteroidal aromatase inhibitor used in postmenopausal women to treat hormone receptor-positive early and advanced breast cancer, either as first-line therapy for advanced disease or as extended adjuvant therapy after tamoxifen. It works by blocking the aromatase enzyme, which reduces the peripheral conversion of androgens to estrogen and lowers circulating estrogen levels, depriving hormone-sensitive tumor cells of the estrogen they need to grow. The typical dose is 1 mg taken orally once daily, with or without food, and treatment for early breast cancer is generally continued for 5 years. Anastrozole is not for use in premenopausal women or during pregnancy, as it can cause fetal harm. Common side effects include hot flashes, joint pain and stiffness, weakness, mood changes, and thinning hair. Because anastrozole lowers estrogen, it can also decrease bone mineral density over time, increasing the risk of osteoporosis and fractures; bone density is typically monitored during treatment, and calcium/vitamin D supplementation or bone-protective therapy may be recommended. It can also raise cholesterol levels, so lipid monitoring may be appropriate.
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Anastrozole works by lowering estrogen levels throughout the body, so most of its side effects relate to estrogen deprivation. Common side effects include hot flashes, joint and muscle pain or stiffness (arthralgia), weakness, headache, mood changes, nausea, and thinning hair.
Bone health: Because estrogen helps protect bone density, long-term anastrozole use can accelerate bone loss and increase the risk of osteoporosis and fractures. Bone mineral density (DEXA scan) is typically assessed before starting treatment and monitored periodically; calcium and vitamin D supplementation, weight-bearing exercise, or bone-protective medications may be recommended.
Cardiovascular and lipid effects: Anastrozole can raise cholesterol levels, so periodic lipid panels may be recommended, particularly in patients with existing cardiovascular risk factors.
Pregnancy: Anastrozole is intended for postmenopausal women only and can cause fetal harm; it should not be used by women who are or may become pregnant.
Patients should notify their physician about new or worsening bone pain, chest pain, sudden vision changes, or signs of an allergic reaction (rash, swelling, difficulty breathing).