Exemestane (Aromasin)

Exemestane is a type of hormone therapy drug. It is also known as Aromasin.

It is a treatment for breast cancer after you have had the menopause (post menopausal).

You pronounce exemestane as ex-e-mes-tane. 

How does exemestane work?

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. Blocking the effects of these hormones can treat breast cancer.

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 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 do you have exemestane?

You have exemestane as tablets. Try to take them at the same time each day, preferably after a meal. Swallow the tablet whole with a drink of water.

You must take tablets according to the instructions your doctor or pharmacist gives you.

Speak to your pharmacist if you have problems swallowing the tablets.

Whether you have a full or an empty stomach can affect how much of a drug gets into your bloodstream.

You should take the right dose, no more or less.

Talk to your healthcare team before you stop taking a cancer drug or if you miss a dose.

How often do you take exemestane?

You take exemestane once a day, usually for a few years. 


You have blood tests before and during your treatment. They check your levels of blood cells and other substances in the blood. They also check how well your liver and kidneys are working.

You might have blood tests to check your hormone levels, vitamin D and calcium levels. 

What are the side effects of exemestane?

Side effects can vary from person to person. They also depend on what other treatments you're having. 

When to contact your team

Your doctor, nurse or pharmacist will go through the possible side effects. They will monitor you during treatment and check how you are at your appointments. Contact your advice line as soon as possible if:

  • you have severe side effects 

  • your side effects aren’t getting any better

  • your side effects are getting worse

Early treatment can help manage side effects better. 

Contact your advice line immediately if you have signs of infection, including a temperature above 37.5C or below 36C.

We haven't listed all the side effects here. Remember it is very unlikely that you will have all of these side effects. But you might have some of them at the same time.

Common side effects

These side effects happen in more than 10 in 100 people (more than 10%). You might have one or more of them. They include:

Increased risk of infection

Increased risk of getting an infection is due to a drop in white blood cells. Symptoms include a change in temperature, aching muscles, headaches, feeling cold and shivery and generally unwell. You might have other symptoms depending on where the infection is.

Infections can sometimes be life threatening. You should contact your advice line urgently if you think you have an infection. 

Difficulty sleeping (insomnia)

If you have difficulty sleeping, it can help to change a few things about how you try to sleep. Try to go to bed and get up at the same time each day and spend some time relaxing before you go to bed. Some light exercise each day may also help. 


Tell your doctor or nurse if you’re feeling depressed. They can arrange for you to talk to someone and give treatment if necessary.

Headaches and dizziness

Let your doctor or nurse know if you have headaches. They can give you painkillers. Don’t drive or operate machinery if you feel dizzy.

Hot flushes and sweats

We have some tips for coping with hot flushes in women. We also explain some of the possible treatments. Talk to your doctor if your hot flushes are hard to cope with. They might be able to prescribe you some medicines.

Tummy (abdominal) pain

Tell your treatment team if you have this. They can check the cause and give you medicine to help. 

Feeling sick

This is usually mild. Let your doctor or nurse know if you have it.

Liver changes

You might have liver changes that are usually mild and unlikely to cause symptoms. They usually go back to normal when treatment finishes. You have regular blood tests to check for any changes in the way your liver is working.

Blood tests can also check any changes to the liver enzymes in your body. 


Let your doctor or nurse know if you are sweating much more than normal. There are treatments and things you can do to help control it.


You may feel pain in different parts of your body such as your muscles and joints. Speak to your doctor or nurse about what painkillers you can take to help with this.

Tiredness and weakness

You might feel very tired and as though you lack energy.

Various things can help you to reduce tiredness and cope with it, for example exercise. Some research has shown that taking gentle exercise can give you more energy. It is important to balance exercise with resting.

Occasional side effects

These side effects happen in between 1 and 10 out of every 100 people (between 1 and 10%). You might have one or more of them. They include:

  • bruising, bleeding gums or nose bleeds due to a drop in the number of platelets in your blood
  • loss of appetite
  • pain in your hands and a weak grip - including numbness and tingling in your hands
  • being sick
  • diarrhoea or constipation
  • indigestion
  • hair loss
  • skin problems including hives and itchy skin
  • pain and swelling of hands and feet
  • thinning of the bones (osteoporosis) which can lead to small cracks in the bones (fractures)

Hormone therapy such as exemestane can increase the risk of osteoporosis. There are things you can do to try to help strengthen your bones. We have more information about the possible ways to help yourself. Speak to your healthcare team if you are worried. 

Rare side effects

This side effects happens in fewer than 1 in 100 people (fewer than 1%). You might have one or more of them. They include:

  • an allergic reaction which can cause a skin rash, feeling hot and shivering, shortness of breath and dizziness – let your doctor or nurse know if this happens
  • feeling very sleepy or drowsy
  • inflammation of the liver, including hepatitis

Coping with side effects

We have more information about side effects and tips on how to cope with them.

What else do you need to know?

Other medicines, foods and drinks

Cancer drugs can interact with medicines, herbal products, and some food and drinks. We are unable to list all the possible interactions that may happen. An example is grapefruit or grapefruit juice which can increase the side effects of certain drugs.

Tell your healthcare team about any medicines you are taking. This includes vitamins, herbal supplements and over the counter remedies. Also let them know about any other medical conditions or allergies you may have.

Pregnancy and contraception

Exemestane might harm a developing baby in the womb. It’s important to use contraception while taking this drug if you have the potential to become pregnant. If it is unclear if you have been through the menopause you will also need to use contraception whilst taking exemestane. 

Talk to your doctor or nurse about effective contraception. They can tell you how long to carry on using contraception after you stop taking exemestane.


It is not known whether this drug comes through into the breast milk. Doctors usually advise that you don’t breastfeed during this treatment.

Treatment for other conditions

If you are having tests or treatment for anything else, always mention your cancer treatment. For example, if you are visiting your dentist.

More information about this treatment

For further information about this treatment and possible side effects go to the electronic Medicines Compendium (eMC) website. You can find the patient information leaflet on this website.

You can report any side effect you have to the Medicines Health and Regulatory Authority (MHRA) as part of their Yellow Card Scheme.

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