What is anastrozole (Arimidex®)?

Anastrozole (Arimidex®) is a hormonal therapy drug used to treat breast cancer in women who have been through the menopause. Sometimes it is used to treat breast cancer in men.

Anastrozole may be used:

  • after other treatments, to reduce the risk of breast cancer coming back 
  • to control breast cancer that has come back or spread to other parts of the body (secondary breast cancer).

It is best to read this information with our general information about hormonal therapies and the type of cancer you have. 

Your doctor will talk to you about this treatment and its possible side effects before you agree (consent) to have treatment. They will explain why you are having anastrozole and how long you will take it for.

How anastrozole works

Hormones are chemicals that our bodies make. They act as messengers and help control how cells and organs work. Hormonal therapies are drugs that change the way hormones are made or how they work in the body.

Many breast cancers rely on the hormone oestrogen to grow. This type of breast cancer is called oestrogen receptor-positive (ER-positive) breast cancer.

Anastrozole reduces the amount of oestrogen in the body. It blocks an enzyme (a type of protein) that helps produce oestrogen in the fatty tissues of the body.

Before a woman goes through the menopause, oestrogen is also made in the ovaries. You may have other types of hormone therapy if you have not been through the menopause.

Taking anastrozole tablets

Anastrozole comes as tablets you can take at home. You take it once a day, with or without food. Try to take it at the same time each day. Swallow the tablet whole with a glass of water.

If you forget to take your tablet, take your next dose as usual. Do not take a double dose.

Anastrozole is a long-term treatment. You may need to take it for several years. Your nurse, doctor or pharmacist will talk to you about your treatment plan. Always take the tablets exactly as explained. This is important to make sure they work as well as possible for you.

Other things to remember about your tablets:

  • Keep them in the original package and at room temperature, away from heat and direct sunlight.
  • Keep them safe and out of sight and reach of children.
  • Get a new prescription before you run out of tablets. Make sure you have enough for holidays.
  • If your treatment is stopped, return any unused tablets to the pharmacist.

About side effects

We explain the most common side effects of this treatment here. We also include some less common side effects.

You may get some of the side effects we mention, but you are unlikely to get all of them. If you are also having treatment with other cancer drugs, you may have some side effects that we have not listed here.

You will see a doctor, nurse or pharmacist regularly while you are having this treatment. Always tell them about any side effects you have. They can give you drugs to help control most side effects. They can also offer advice to help you cope.

Most side effects can be managed. But sometimes side effects are harder to control. It is important not to stop taking hormonal therapy without telling your doctor. If side effects cannot be managed, your doctor may suggest you take a different type of hormonal therapy.

Serious and life-threatening side effects

Some cancer treatments can cause severe side effects. Rarely, these may be life-threatening. Your cancer doctor or nurse can explain the risk of these side effects to you.

Contact the hospital

Your nurse will give you telephone numbers for the hospital. If you feel unwell or need advice, you can call them at any time of the day or night. Save these numbers in your phone or keep them somewhere safe.

More information

We cannot list every side effect for this treatment. There are some rare side effects that are not listed. You can visit the electronic Medicines Compendium (eMC) for more detailed information.

Common side effects

Hot flushes and sweats

Hot flushes are a common side effect of this treatment. During a flush, your neck and face may feel warm and look red. Flushes may last from a few seconds up to 10 minutes. You may have sweats and then feel cold and clammy. Some people feel anxious or irritable during a hot flush.

There are things you can do to try to reduce flushes:

  • Wear clothes made from natural fabrics, such as cotton.
  • Wear layers of clothes that you can remove if you feel hot.
  • Use cotton bed sheets and have layers of bedding that you can remove if you feel hot.
  • Keep room temperatures cool or use a fan.
  • Have cold drinks rather than hot ones. Try to avoid drinks with caffeine in them.

You may have fewer hot flushes and sweats as your body adjusts to hormonal treatment. Or your doctor can prescribe drugs to help. Flushes and sweats usually stop a few months after treatment finishes, but some people continue to have them.

We have more information about coping with hot flushes. Women can read more about coping with hot flushes in our information about managing menopausal symptoms.

Muscle or joint pain

You may get pain in your muscles or joints. If this happens, tell your doctor so they can give you painkillers. Being physically active may help with the pain and keep your joints flexible. Keeping to a healthy weight may help too. Tell your doctor or nurse if the pain does not get better.

Tiredness

Feeling tired is a common side effect. Try to pace yourself and plan your day so you have time to rest. Gentle exercise, like short walks, can give you more energy. If you feel sleepy, do not drive or operate machinery.

Feeling sick (nausea) or being sick (vomiting)

Any sickness is usually mild. Tell your doctor or nurse if you this happens. Try taking your anastrozole tablets with food or at night.

Loss of appetite

This treatment can affect your appetite. If you do not feel like eating three big meals a day, try to eat small, frequent meals or snacks instead.

Changes to your taste

You may get a bitter or metal taste in your mouth. Sucking sugar-free sweets may help with this. Some foods may taste different or have no taste. Try different foods to find out what tastes best to you. Taste changes usually get better after treatment finishes. Your nurse can give you more advice.

Diarrhoea

This is usually mild. If it does not get better, your doctor can prescribe drugs to control it. Make sure you drink at least 2 litres (31/2 pints) of fluids every day if you have diarrhoea.

Headaches

This treatment may cause headaches. If this happens, tell your doctor or nurse. They can give you painkillers.

Skin changes

This treatment may affect your skin. It may cause a rash, which might be itchy. Your doctor or nurse can tell you what to expect. If your skin feels dry, try using an unperfumed moisturising cream every day.

Always tell your doctor or nurse about any changes to your skin. They can give you advice and may prescribe creams or medicines to help. Skin changes usually improve when treatment finishes.

Hair thinning

Your hair may become thinner when you are taking this treatment. This is usually mild. Ask your nurse for advice if you are worried about this.

Vaginal bleeding or dryness

This treatment can cause vaginal changes. You may have bleeding when you start this treatment, or if you change to it from another treatment. If bleeding continues for more than a few days, tell your doctor or nurse.

You can use non-hormonal creams, gels or lubricants to help with vaginal dryness and any discomfort during sex. You can buy these from a chemist, or your doctor can prescribe them. We have more information about cancer and sex.

Pain, numbness and tingling in hand and fingers

You may get pain, numbness or tingling in the hand and fingers. These symptoms may be caused by carpal tunnel syndrome, which is caused by pressure on a nerve in the wrist. It is more common in people taking this drug. Tell your doctor if you have these symptoms.

Raised cholesterol level

This treatment can raise the level of cholesterol (a fatty substance) in the blood. You may have a blood test to check the level of cholesterol. Your doctor may give you medicines to control your cholesterol levels.

Effects on the liver

Anastrozole can sometimes cause changes in how the liver works. Your doctor will arrange for you to have regular blood tests to check your liver is working properly. You are very unlikely to notice any problems.

Allergic reaction

Some people have an allergic reaction while having this treatment. Signs of a reaction can include:

  • feeling hot or flushed
  • a skin rash
  • itching
  • shivering
  • feeling dizzy
  • a headache
  • feeling breathless.

If you feel unwell or have any of these signs, tell a doctor or nurse straight away. Do not take any more of this treatment until you have spoken to them.

Possible side effects of long-term anastrozole treatment

Bone thinning (osteoporosis)

If you take this treatment for several months or more, you may get bone thinning. This is called osteoporosis. This can increase your risk of a broken bone (fracture). You may have bone density scans to check your bone health before and during treatment.

Doing regular exercise, such as walking, can improve your bone health. Eating a healthy diet can help too. Your doctor may prescribe drugs called bisphosphonates to help protect your bones. They may also advise you to take calcium and vitamin D supplements.

Other information

Blood clot risk

Cancer and some cancer treatments can increase the risk of a blood clot. Symptoms of a blood clot include:

  • pain, redness or swelling in a leg or arm
  • breathlessness
  • chest pain.

If you have any of these symptoms, contact a doctor straight away.

A blood clot is serious, but can be treated with drugs that thin the blood. Your doctor or nurse can give you more information.

Other medicines

Some medicines can affect how this treatment works or be harmful when you are having it. Always tell your cancer doctor about any drugs you are taking or planning to take, such as:

  • medicines you have been prescribed
  • medicines you buy in a shop or chemist
  • vitamins, herbal drugs and complementary therapies.

Tell other doctors, pharmacists or dentists who prescribe or give you medicines that you are having this cancer treatment.

You can visit the electronic Medicines Compendium (eMC) for more detailed information about your treatment.

Problems with lactose

These tablets contain a type of sugar called lactose. If you have been told by a doctor that you cannot digest some sugars or are lactose intolerant, talk to your doctor before taking this drug.

Medical and dental treatment

If you need medical treatment for any reason other than cancer, always tell the doctors and nurses that you are having cancer treatment. Give them the contact details for your cancer doctor so they can ask for advice.

If you think you need dental treatment, talk to your cancer doctor or nurse. Always tell your dentist you are having cancer treatment.