Anastrozole (Arimidex) for breast cancer: the complete patient guide

Anastrozole, sold under the brand name Arimidex and as many generics, is a hormone therapy tablet for hormone-receptor-positive breast cancer. It belongs to a group of medicines called aromatase inhibitors. After menopause, the ovaries no longer make much oestrogen, but the body still produces some in fat, muscle and other tissues using an enzyme called aromatase. Anastrozole blocks this enzyme, lowering oestrogen levels so that cancer cells that depend on oestrogen are starved of a growth signal. It is used after surgery for early breast cancer to lower the chance of the cancer coming back, usually for about five years, and sometimes after a few years of tamoxifen. It is also used to control breast cancer that has spread, and in some countries it is offered to postmenopausal women at high risk to lower their chance of developing breast cancer. Younger women can take it only if their ovaries are switched off with injections or surgery. It is a small tablet taken once a day, with or without food, and most people take it at home while carrying on with normal life. The commonest side effects are hot flushes, joint pain and stiffness, tiredness, vaginal dryness and gradual thinning of the bones, so your team will usually check your bone health and vitamin D. Anastrozole is not chemotherapy, it does not usually cause hair loss or lower blood counts, and it must not be taken with tamoxifen or oestrogen-containing products.

Who it is for

Women after menopause, or younger women with ovarian suppression, who have hormone-receptor-positive breast cancer.

How it is taken

One tablet a day, at a time that suits you, usually for several years.

What to watch for

Joint pain, hot flushes and bone thinning are the effects most women notice or need checking.

Anastrozole is a well-studied and effective medicine, but it is a long commitment with real side effects for many women.

It lowers risk rather than removing it

Anastrozole reduces the chance of cancer returning. Some women still have a recurrence despite taking every tablet, and many would not have had one anyway.

Side effects are common

Joint pain and stiffness affect a large share of women, and some find it hard to continue. Help is available, including switching to another tablet.

There is no test to show it is working

Its value comes from taking it steadily over years, which can be hard when you feel well.

What this page cannot tell you

It cannot tell you whether anastrozole is right for you. Your oncologist can.

Most side effects can wait for a routine visit, but some need prompt attention.

Seek urgent help

For swelling of the face, lips or throat, a severe rash with blisters or peeling skin, or yellowing of the skin or eyes.

Contact your team soon

For new bone pain, a fracture after a minor fall, vaginal bleeding, or joint pain that stops you doing everyday tasks.

Raise at your next visit

Hot flushes, mild stiffness, low mood, poor sleep or vaginal dryness that are affecting your quality of life.