Aromasin (Exemestane)

How does it work?

Aromasin tablets contain the active ingredient exemestane, which is a type of medicine called an aromatase inhibitor. It works by preventing the action of an enzyme in the body called the aromatase enzyme.

The aromatase enzyme is involved in producing the female sex hormone, oestrogen, in women who have gone through the menopause. The enzyme converts the sex hormones androstenedione (produced by the ovaries), and testosterone, into oestrogen. Exemestane prevents this conversion by blocking the action of the aromatase enzyme. This causes a reduction in oestrogen levels.

Most breast cancers are sensitive to oestrogen, and their growth is stimulated by this hormone. By lowering the levels of oestrogen in the body, exemestane starves the breast cancer cells and stops them from growing. Exemestane is only effective in treating breast cancers that are sensitive to oestrogen (these are sometimes called oestrogen receptor positive cancers).

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

Exemestane is used to treat breast cancer in women who are postmenopausal, either naturally, or as a result of medical treatment. It is used for treating women with early invasive cancers, after they have completed two to three years of treatment with tamoxifen. It is also used to treat advanced cancers, where the cancer has continued to grow despite using other anti-oestrogen medicines.

What is it used for?

  • Early invasive breast cancer in postmenopausal women who have had two to three years of treatment with tamoxifen
  • Advanced breast cancer in postmenopausal women where other anti-oestrogen medicines have not been effective


  • This medicine might make you feel sleepy, dizzy or weak and could therefore affect your mental or physical ability to safely drive or operate machinary. You should be aware of how you react to this medicine before driving or operating machinary.
  • Oestrogen helps protect bone strength. After the menopause, oestrogen levels fall naturally and this can cause your bones to become weaker. As this medicine further reduces oestrogen levels, it may cause a further loss of bone strength. For this reason, women who have osteoporosis, or risk factors for developing osteoporosis, should have their bone mineral density assessed before this medicine is started. If bone loss increases during treatment this may increase the risk of breaking a bone and your doctor may therefore want you to take additional medicine to help protect your bones.

Use with caution in

  • Decreased kidney function
  • Decreased liver function
  • Osteoporosis and women at risk of osteoporosis

Not to be used in

  • Pre-menopausal women
  • Pregnancy
  • Breastfeeding
  • Rare hereditary problems of fructose intolerance, glucose-galactose malabsorption or sucrase-isomaltase insufficiency (Aromasin tablets contain sucrose)

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 is only for women who have passed the menopause and should not be used during pregnancy or breastfeeding. Seek medical advice from your doctor.

Label warnings

  • Take this medication with or after food.

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
  • Fatigue
  • Joint pain
  • Difficulty in sleeping (insomnia)
  • Headache
  • Increased sweating
  • Disturbances of the gut such as nausea, vomiting, constipation, diarrhoea, indigestion or abdominal pain
  • Loss of appetite
  • Dizziness
  • Depression
  • Carpal tunnel syndrome
  • Skin rashes
  • Hair loss (alopecia)
  • Swelling of the legs and ankles due to excess fluid retention (peripheral oedema)
  • Pain
  • Weakness
  • Sleepiness
  • Disturbances in the normal levels of blood cells in the blood

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?

You should tell your doctor or pharmacist what medicines you are taking, including those bought without a prescription and herbal medicines, before you start treatment with this medicine. Likewise, you should always check with your doctor or pharmacist before taking any new medicines during treatment with this one, so they can check that the combination is safe.

Medicines that contain oestrogens, for example hormone replacement therapy (HRT), should not be taken in combination with this medicine, as they will oppose its action and make it less effective at treating the cancer.

The following medicines may potentially reduce the blood level of this medicine and could make it less effective:

  • rifampicin
  • phenytoin
  • carbamazepine
  • the herbal remedy St John's wort (Hypericum perforatum).

Other medicines containing the same active ingredient

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