Anastrozole
2 medicines
Anastrozole is an aromatase inhibitor used to treat hormone-receptor-positive breast cancer in postmenopausal women; it lowers estrogen enough to thin bone, so bone density is checked before and during treatment.
Key facts
- Anastrozole (sold as Arimidex) is an aromatase inhibitor: it blocks the enzyme that makes estrogen in fat and other tissues after menopause, sharply lowering circulating estrogen.
- It's taken as one tablet a day, usually for up to 5 years, as treatment for hormone-receptor-positive breast cancer.
- Anastrozole speeds up bone loss and raises fracture risk; bone density (DEXA) scans are part of routine monitoring before and during treatment.
- Seek urgent care for chest pain, sudden shortness of breath, or sudden weakness, numbness, or slurred speech.
What anastrozole treats
Anastrozole treats hormone-receptor-positive breast cancer in postmenopausal women: as initial treatment for early-stage disease, to reduce the chance that early breast cancer returns after surgery, and for cancer that has spread. It is not used before menopause, when the ovaries still make estrogen that the drug cannot block.
How anastrozole works
After menopause the ovaries stop producing estrogen, but an enzyme called aromatase still converts other hormones into small amounts of estrogen in fat and other tissues. Hormone-receptor-positive breast cancers depend on this estrogen to grow. Anastrozole blocks aromatase, cutting estrogen to very low levels and depriving these cancer cells of the signal they need to divide.
Before you take it
- Anastrozole is for postmenopausal women only; it does not work reliably before menopause and must not be used in pregnancy, which it can harm.
- Tell your doctor about osteoporosis, previous fractures, or high cholesterol; low estrogen thins bone and can raise cholesterol.
- Expect a bone density scan before starting and periodically during treatment; your doctor may recommend calcium, vitamin D, or a bone-protecting medicine.
- Mention other hormone treatments, including tamoxifen, since combining them is not usually appropriate.
Side effects
Common effects include hot flushes, joint and muscle stiffness or aches, fatigue, and mild nausea.
Stop and seek urgent medical care for any of these:
- New bone pain or a fall that could signal a fracture.
- Chest pain, sudden shortness of breath, or a fast or irregular heartbeat.
- Sudden weakness, numbness, or difficulty speaking.
- Severe swelling of the legs.
Safety essentials
- Anastrozole's defining risk is accelerated bone loss: fracture risk rises during treatment, so bone density scans before and during treatment are a required part of care, not optional.
- Take calcium and vitamin D if advised, and stay active with weight-bearing exercise to help protect bone.
- Have cholesterol and cardiovascular risk checked periodically, since long-term low estrogen affects both.
This page is educational and does not replace advice from a doctor or pharmacist who knows your health history.