Side effects of exemestane (Aromasin)

Common side effects of exemestane include:

• Reduced number of white blood cells
• Aching or pain in the joints and muscles
• Menopausal symptoms
• Low mood and depression
• Extreme tiredness
• Difficulty sleeping
• Osteoporosis (thinning of the bone)
• Headaches
• Dizziness
• Nausea and vomiting
• High cholesterol
• Diarrhoea and constipation
• Loss of appetite, indigestion and heartburn
• Carpal tunnel syndrome
• Changes to hair or facial hair
• Skin changes
• Changes to the liver 
• Vaginal bleeding
• Swelling of hands and feet

Reduced number of white blood cells

Exemestane can reduce the number of white blood cells. This may increase the risk of getting an infection.

Symptoms of an infection include a change in temperature, aching muscles, headaches, feeling cold and shivery and generally unwell.

You should contact your GP or treatment team if you think you have an infection.

Aching or pain in the joints and muscles 

You may have aching or pain in your joints or muscles. This is often mild and temporary but for some people it can be more severe and longer lasting.

Find out more about joint and muscle pain including tips for managing pain.

Menopausal symptoms 

You may have menopausal symptoms such as:

• Hot flushes
• Night sweats

Find out more about menopausal symptoms. 

Low mood and depression 

You may notice you have a low mood or feel depressed. It can be difficult to know whether this is because of the medication or other reasons, such as menopausal symptoms or dealing with your breast cancer diagnosis.

Some people find mindfulness or exercise improves their mood.

You can talk to your GP or treatment team about how to manage a change in mood. They can refer you for counselling or may suggest you take an antidepressant drug. Your breast care nurse may also be able to help or tell you about support services in your area.

Read more about coping with breast cancer emotionally.

Extreme tiredness (cancer-related fatigue)

Fatigue is extreme tiredness that doesn’t go away with rest or sleep. It’s a very common side effect of exemestane and may continue for weeks or months after you stop taking it.

If you think you have fatigue, tell your GP or treatment team. They can assess you and offer advice on how to manage your energy levels.

Find out more about managing fatigue.

Difficulty sleeping 

If you have difficulty sleeping (insomnia), some simple changes to your routine may help, like:

• Limiting caffeine in the afternoon and evening
• Keeping your room dark and quiet
• Going to bed and getting up at a set time each day

Relaxation exercises can also be helpful. There are CDs, podcasts and phone apps that can guide you through these techniques. 

If you continue to have difficulty sleeping your GP may prescribe something to help you sleep.

Find out more about having trouble sleeping during breast cancer treatment.

Osteoporosis (thinning of the bone) 

Exemestane reduces the amount of oestrogen in the body. Over time, a lack of oestrogen can cause osteoporosis. This leads to bones becoming weaker and more likely to break (fracture).

Your treatment team may check the strength and thickness (density) of your bones with a DEXA (dual energy x-ray absorptiometry) scan before or shortly after you start taking exemestane. If you are taking bisphosphonates as part of your treatment, you will not need a scan.

Find out more about looking after your bones and osteoporosis and breast cancer treatment.

Headaches

Exemestane can sometimes cause headaches. Mild pain relief such as paracetamol may help with headaches.

Dizziness 

Exemestane may cause dizziness. If you feel dizzy, avoid driving. If dizziness continues, see your GP.

Nausea and vomiting 

Exemestane may also make you feel sick (nausea) or be sick (vomit).

These symptoms usually improve or become easier to manage over time. Taking exemestane after food can help reduce nausea.

High cholesterol 

Exemestane may cause the level of cholesterol in the blood to rise, although this doesn’t usually need treatment. If you have a history of high cholesterol you may want to discuss this with your treatment team or GP. 

Diarrhoea and constipation

If you have diarrhoea, it’s important to drink enough fluids. Your GP or treatment team can prescribe medication to help with diarrhoea.

It’s also important to keep active and eat a high-fibre diet to avoid constipation.

Loss of appetite, indigestion and heartburn

If you lose your appetite, you may find eating small frequent meals or snacks helps keep up your food intake.

You may also have indigestion or heartburn (a painful burning feeling in the chest after eating).

If you struggle to maintain a healthy weight, ask your GP or treatment team about being referred to a dietitian. 

Find out more about diet and breast cancer treatment.

Carpal tunnel syndrome 

Carpal tunnel syndrome (CTS) is pressure on a nerve in your wrist. This causes pain, tingling and numbness in your arm, hand or fingers.

Speak to your GP or treatment team if you have any of these symptoms.

Sometimes it can go away on its own, but it can take months to get better. Some people find using a wrist splint helpful.

Changes to hair or facial hair

You may have some hair loss or thinning while taking exemestane. A small number of women notice an increase in downy facial hair. 

Find out more about hair loss and thinning.

Skin changes

You may develop a skin rash or itching while taking exemestane. This usually goes away when your treatment finishes. Your pharmacist, GP or treatment team can tell you what products you can use on your skin to help.

Changes to the liver

Exemestane can occasionally cause changes to how the liver works. These changes are usually mild and unlikely to cause any symptoms. Once you finish your treatment your liver will usually go back to normal.

Vaginal bleeding

Vaginal bleeding can happen in the first few weeks after starting exemestane. It most commonly occurs when changing from one hormone therapy to another.

Vagina dryness may also cause vaginal bleeding.

If the vaginal bleeding continues for more than a few days, tell your treatment team. 

Swelling of hands and feet (oedema)

You can get swollen hands and feet. If you notice this, or any other swelling, let your GP know.

Blood clots

People with breast cancer have a higher risk of blood clots such as a DVT (deep vein thrombosis). If you have a DVT, there’s a risk part of the blood clot could break away and travel to the lung. This is known as a pulmonary embolism (PE).

Blood clots can be life-threatening and should be treated quickly.

Everyone reacts differently to drugs and some people have more side effects than others. These side effects can usually be managed and those described here will not affect everyone.

If you’re worried about side effects, regardless of whether they’re listed here, talk to your treatment team.

Do different brands of exemestane cause different side effects?

Exemestane is made by different manufacturers.

Some of the tablets may have different additional ingredients, such as preservatives. This means that the colour, shape, size and sometimes taste of the tablets can differ between brands. However, this does not change the effectiveness of the treatment.

Some people say they notice a change in the side effects they have if they take exemestane made by a different manufacturer. This suggests that some people find exemestane produced by one manufacturer seems to suit them better than another.

You can ask your GP if they can prescribe the brand you feel suits you best. However, you may also need to check if a pharmacy has the brand in stock or would be willing to try to get it for you.

Side effects caused by exemestane will be different for each person. You may find your side effects reduce after stopping exemestane. Or they may continue after treatment finishes.

You may also have side effects caused by other treatments or individual circumstance, such as the menopause.

If you're worried about any long-term side effects after stopping exemestane, speak to your treatment team or GP.