Arimidex (Anastrazole)

How does it work?

Arimidex tablets contain the active ingredient anastrozole, which is a type of medicine known as a non-steroidal aromatase inhibitor. It works by preventing the action of an enzyme in the body called the aromatase enzyme.

The aromatase enzyme is involved in the production of the female sex hormone, oestrogen. In women who have passed the menopause, oestrogen is mainly produced by this enzyme. In postmenopausal women the aromatase enzyme converts the sex hormones androstenedione (produced by the ovary), and testosterone, into oestrogen. Anastrozole prevents this conversion by blocking the action of the aromatase enzyme. This causes oestrogen levels in the body to fall.

Many breast cancers are sensitive to oestrogen, and they need this hormone to grow. These types of breast cancer are termed 'hormone receptor positive'. Oestrogen binds to oestrogen receptors on the breast cancer cells and causes changes within the cells that result in faster growth of the cancer.

By lowering the levels of oestrogen in the body, anastrozole effectively starves the breast cancer cells, thus helping to stop them grow.

Anastrazole helps prevent breast cancer from spreading to other areas of the body and also reduces risk of developing cancer in the other breast.

Anastrazole is only effective in postmenopausal women, since before the menopause oestrogen is mainly produced by the ovaries and not by the aromatase enzyme.

What is it used for?

  • Advanced breast cancer in women who have passed the menopause
  • Treating postmenopausal women who have had surgery to remove early hormone receptor positive breast cancer. It can either be used for five years immediately following the surgery, or after two to three years of taking tamoxifen.


  • If there is any doubt as to whether or not your menopause has taken place, you should be given a test to measure your hormone levels before this medicine is started.
  • This medicine may make you feel weak or sleepy. If affected you should take care performing potentially hazardous tasks such as driving or operating machinery.
  • This medicine may cause vaginal bleeding in the first few weeks if you have changed from an existing hormonal treatment. If any bleeding persists, consult your doctor.
  • As anastrozole lowers oestrogen levels it may also cause a decrease in bone mineral density, which for some women could increase the risk of breaking a bone. If you have osteoporosis or are at risk of developing osteoporosis (for example if you had an early menopause, have a family history of osteoporosis, are a smoker, have a small thin frame, or have had prolonged treatment with corticosteroids such as prednisolone), you should have your bone mineral density monitored regularly with bone scans while taking this medicine.

Use with caution in

  • Osteoporosis
  • Women with risk factors for osteoporosis (eg early menopause, family history, smokers, small thin frame, long-term use of corticosteroids)

Not to be used in

  • Moderate to severe liver disease
  • Moderate to severely decreased kidney function
  • Pre-menopausal women
  • Pregnancy
  • Breastfeeding.
  • Rare hereditary problems of galactose intolerance, the Lapp lactase deficiency or glucose-galactose malabsorption (Arimidex tablets contain lactose).

This medicine should not be used if you are allergic to one or any of its ingredients. Please inform your doctor or pharmacist if you have previously experienced such an allergy.If you feel you have experienced an allergic reaction, stop using this medicine and inform your doctor or pharmacist immediately.

Pregnancy and Breastfeeding

Certain medicines should not be used during pregnancy or breastfeeding. However, other medicines may be safely used in pregnancy or breastfeeding providing the benefits to the mother outweigh the risks to the unborn baby. Always inform your doctor if you are pregnant or planning a pregnancy, before using any medicine.

  • This medicine should not be used during pregnancy or breastfeeding. Seek medical advice from your doctor.

Side effects

Medicines and their possible side effects can affect individual people in different ways. The following are some of the side effects that are known to be associated with this medicine. Because a side effect is stated here, it does not mean that all people using this medicine will experience that or any side effect.

  • Hot flushes
  • Weakness or loss of strength (asthenia)
  • Joint pain or stiffness
  • Mood disturbances
  • Vaginal dryness
  • Hair thinning
  • Rash
  • Headache
  • Diarrhoea
  • Nausea and vomiting
  • Loss of appetite
  • Vaginal bleeding
  • Sleepiness (somnolence)
  • Raised cholesterol levels
  • Decreased bone density
  • Very rare severe skin reactions (eg Stevens-Johnson Syndrome)

The side effects listed above may not include all of the side effects reported by the drug's manufacturer.For more information about any other possible risks associated with this medicine, please read the information provided with the medicine or consult your doctor or pharmacist.

How can this medicine affect other medicines?

It is important to tell your doctor or pharmacist what medicines you are already taking, including those bought without a prescription and herbal medicines, before you start treatment with this medicine. Similarly, check with your doctor or pharmacist before taking any new medicines (including herbals) while taking this one, to ensure that the combination is safe.

This medicine should not be taken in combination with tamoxifen, as tamoxifen may decrease the effect of this medicine if it is taken at the same time.

Oestrogen-containing treatments (eg hormone replacement therapy or HRT) should not be taken with anastrozole, as they would counteract its action.

Gonadorelin (LHRH) analogues such as buserelin, goserelin, leuprorelin and triptorelin should not be used in combination with this medicine, unless as part of a clinical trial. This is because there is no data on the effect of such combinations.

Other medicines containing the same active ingredient

There are currently no other medicines available in the UK that contain anastrozole as the active ingredient.