Anastrozole (Arimidex)

Anastrozole is a type of hormone therapy. You pronounce it as an-ass-tro-zol. It is also known as Arimidex.

It is a treatment for 

  • early breast cancer to reduce the risk of it coming back (recurring)
  • secondary breast cancer Open a glossary item to control the growth of the cancer

Women who have a medium or high risk of developing breast cancer because of a family history might have anastrozole. This is to reduce the risk of breast cancer from developing. This is for women who are post menopausal. Open a glossary item

Anastrozole for women with breast cancer

Women with breast cancer usually only have anastrozole when they are post menopausal.

Less often, some women who have not been through the menopause may also have anastrozole. In this instance, they have it in combination with other treatments that stop the ovaries working.

Anastrozole for men with breast cancer

Anastrozole might sometimes be used to treat breast cancer in men. Breast cancer is very rare in men. So very little is known about the side effects of this drug in men. Doctors expect the effects to be similar to those listed on this page. But do talk to your cancer specialist who may have experience in treating other men with hormone therapy.

How does anastrozole work?

Oestrogen is known more as a female hormone, but men also have a small amount of oestrogen. Oestrogen stimulates some breast cancers to grow. These are called hormone sensitive or hormone receptor positive breast cancers. 

Anastrozole lowers the level of oestrogen. It does this by blocking a substance in the body called aromatase. Anastrazole belongs to a type of hormone therapy called aromatase inhibitors. Lowering the level of oestrogen aims to prevent, stop or slow the growth of these cancers.

How do you have anastrozole?

You have anastrozole as tablets.

You should swallow your tablets whole with a drink of water. Try to take them at the same time each day. You can take them before, with, or after food.

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

You should take the right dose, not 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 have anastrozole?

You usually take anastrozole once a day. You usually take it for up to 5 years.


You might have blood tests before starting treatment and during your treatment. They check your general health and might check your levels of blood cells and other substances in the blood.

Side effects

Side effects can vary from person to person. They also depend on what other treatment you are having. 

When to contact your team

Your doctor, nurse, or pharmacist will go through the possible side effects. They will monitor you closely 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.

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 happens in more than 10 out of 100 people (more than 10%). You might have one or more of them. They include:


Tell your healthcare team if you keep getting headaches. They can give you painkillers to help.

Hot flushes and sweats

We have some tips for coping with hot flushes in women and hot flushes in men. This information also includes 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.

Feeling sick 

You might feel sick (nauseous). You may also be sick, but this is less common. Your healthcare team can prescribe anti sickness medicines if it continues or is severe.

Skin rash

Skin problems include a skin rash, dry skin and itching. This usually goes back to normal when your treatment finishes. Your healthcare team can tell you what products you can use on your skin to help.

Painful, stiff or inflamed joints

You might have pain or stiffness in your joints. Speak to your healthcare team about painkillers to help with this.

Some people may develop bone conditions such arthritis. Talk to your team about your risk and what you can do to prevent or manage these conditions.

Tiredness and weakness (fatigue) 

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.

Bone loss (osteoporosis)

The bones can become more brittle and thinner. Having thinner bones makes them more at risk of breaking (fracture). After the menopause Open a glossary item the levels of the sex hormone oestrogen decrease. This increases bone loss. 

Talk to your team about your risk and what you can do to prevent or manage this condition.


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

Occasional side effects

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

  • allergic reaction that can cause a rash, shortness of breath, redness or swelling of the face and dizziness - some allergic reactions can be life threatening, so alert your nurse or doctor if you notice any of these symptoms
  • diarrhoea
  • vaginal dryness or bleeding – bleeding might in the first few weeks of treatment. Let your team know if this continues for longer
  • hair thinning
  • liver changes – you have regular blood tests to check this and they usually don’t cause any symptoms
  • carpal tunnel syndrome- this can cause tingling, numbness, pain, feeling cold and weakness in part of the hands and fingers
  • loss of appetite
  • raised cholesterol in the blood
  • feeling sleepy
  • bone and muscle pain
  • sensation changes - your skin might feel tingly or numb
  • changes in taste or loss of taste

Rare side effects

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

  • liver inflammation (hepatitis)
  • trigger finger (finger or thumb fixed in a bent position)
  • high levels of calcium in the blood
  • inflammation of blood vessels in the skin which can cause a purple or reddish rash and sometimes blisters
  • a severe skin reaction that may start as tender red patches which leads to peeling or blistering of the skin. You might also feel feverish and your eyes may be more sensitive to light. This is serious and could be life threatening.
  • swelling of the different parts of the body – this is due to swelling of the deeper layers of the skin caused by a build up of fluid (angioedema)

Coping with side effects

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

What else do I need to know?

Other medicines, foods and drink

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.


It is not known whether this treatment affects fertility Open a glossary item in people. Talk to your doctor before starting treatment if you think you may want to have a baby in the future.

Pregnancy and contraception

It is unknown whether treatment may or may not harm a baby developing in the womb. It is important not to become pregnant or get someone pregnant while you are having treatment. Let your team know straight away if you or your partner become pregnant while having treatment.

Talk to your doctor or nurse about effective contraception you can use during treatment. Ask how long you should use it before starting treatment and after treatment has finished.


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.

Related links