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Exemestane (Aromasin)

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This page tells you about the hormone therapy exemestane and its possible side effects. There are sections about


What exemestane is

Exemestane is also called Aromasin. It is a type of hormone therapy drug called an aromatase inhibitor and is used to treat breast cancer. It is only suitable for women who have had their menopause.

There is general information about hormone therapies in the cancer treatment section.


How exemestane works

Many breast cancers are stimulated to grow by the female sex hormones oestrogen and progesterone. These breast cancers are called hormone sensitive or hormone receptor positive and can be treated with drugs that block the effects of these hormones.

In women who have had their menopause, oestrogen is mainly produced by changing androgens (sex hormones produced by the adrenal glands) into oestrogens. This process is called aromatisation and happens mainly in the fatty tissues, muscle and the skin. It needs a particular enzyme called aromatase.

Exemestane blocks the process of aromatisation. So it lowers the amount of oestrogen in the body. In early breast cancer, taking exemestane can help to stop breast cancer coming back. In advanced breast cancer the cancer cells may grow more slowly or stop growing completely.


How you have exemestane

You take exemestane as a tablet, once a day after a meal. You need to take them at approximately the same time each day. You usually take them for a few years.

It is very important that you take tablets according to the instructions your doctor or pharmacist gives you. For example, whether you have a full or empty stomach can affect how much of a drug gets into your bloodstream. You should take the right dose, not more or less. And never stop taking a cancer drug without talking to your specialist first.

If you accidentally take more exemestane than you should, let your doctor know straight away.

If you forget to take a tablet, take it as soon as you remember. If it is nearly time for the next dose, take that tablet at the usual time. Don't take a double dose to make up for the missed one.


Tests during treatment

You have blood tests before starting treatment and regularly during your treatment. The tests check your levels of blood cells. They may also check how well your liver and kidneys are working.


About side effects

We've listed the side effects associated with exemestane below. You can use the links to find out more about each side effect. Where there is no link, please go to our cancer drug side effects section or click on search at the top of the page.

You may have 1 or 2 or a few side effects. They may be mild or more severe. A side effect may get better or worse through your course of treatment, or more side effects may develop as the course goes on. This depends on

  • How many times you've had the drug before
  • Your general health
  • The amount of the drug you have (the dose)
  • Other drugs you are having

Tell your doctor or nurse straight away if any of the side effects get severe.


Common side effects

More than 10 in every 100 people have one or more of these effects.


Occasional side effects

Between 1 and 10 in every 100 people have one or more of these.

  • Loss of appetite
  • Lowered interest in sex
  • Stomach ache
  • Indigestion
  • Skin rashes – these are usually mild. Let your doctor or nurse know if you have a rash. This happens in about 1 in 10 women taking exemestane (10%)
  • Feeling dizzy – about 1 in 10 women (10%) have some dizziness. Don't drive or operate machinery if you have this
  • Feeling very sad, including depression
  • Loss of bone strength – this is caused by a lack of oestrogen over a long period of time and bones may break more easily. You should have a DEXA scan to check your bone density before you start treatment
  • Diarrhoea or constipation – if this happens it is usually mild. You should drink plenty of fluids.
  • Vaginal bleeding occurs in less than 1 in 20 women (5%) – this mainly happens during the first few weeks of treatment when women have changed from one type of hormone therapy to another. Tell your doctor or nurse if the bleeding continues
  • Swelling in the hands and feet caused by a build up of fluid
  • Carpal tunnel syndrome – let your doctor or nurse know if you have any pain, tingling or weakness in your hands

Rare side effects

Fewer than 1 in 100 people have these effects.

  • Drowsiness
  • Muscle weakness
  • Inflammation of the liver – let your doctor know straight away if you feel generally unwell, or have yellowing of the skin and eyes, itching, abdominal pain on the right hand side, and loss of appetite

Important points to remember

Talk to your doctor, pharmacist or nurse about all your side effects so that they can help you manage them. You should have a contact number for your chemotherapy nurse, clinic or ward nurse. You can ring if you have any questions or problems. They can give you advice or reassure you. If in doubt, call them.

Other medicines

Tell your doctor about any other medicines you are taking, including vitamins, herbal supplements and over the counter remedies. Some drugs can react together.

Do not take hormone replacement therapy while you are having exemestane treatment.

Pregnancy and contraception

This drug may harm a baby developing in the womb. It is important not to become pregnant while you are having treatment with this drug and for a few months afterwards. Talk to your doctor or nurse about effective contraception before starting treatment.


Do not breastfeed during this treatment because the drug may come through in the breast milk.

Sugar intolerance

Exemestane contains a small amount of sucrose (a type of sugar). Tell your doctor if you have an intolerance to any type of sugar.


More information about exemestane

This page does not list all the very rare side effects of this treatment that are very unlikely to affect you. For further information look at the Electronic Medicines Compendium website at www.medicines.org.uk.

If you have a side effect not mentioned here that you think may be due to this treatment you can report it to the Medicines Health and Regulatory Authority (MHRA) at www.mhra.gov.uk.

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Updated: 24 January 2014