What is anastrozole?

Anastrozole is a man-made drug which is used in the treatment of breast cancer in women who have had their menopause (change of life). It is mainly used to treat women who have advanced breast cancers or breast cancer that has come back after initial treatment (breast cancer that has spread). Sometimes it is used in early breast cancer.

Anastrazole is a type of hormonal therapy. Hormonal therapies work by interfering with the production or action of particular hormones. Hormones are substances produced naturally by the body. They act as chemical messengers and help to control the activity of cells and organs.

How does anastrozole work?

Many breast cancers need supplies of the hormone oestrogen to grow. In women who have passed the menopause the main source of oestrogen is through the conversion of androgens (sex hormones produced by the adrenal glands) into oestrogens. This is carried out by an enzyme called aromatase. This conversion process is known as aromatisation, and happens mainly in the fatty tissues of the body.

Anastrozole blocks the process of aromatisation and preventing this chemical change. This results in a reduction in the amount of oestrogen in the body. For this reason anastrozole is known as an aromatase inhibitor.

How it is taken

Anastrozole is a tablet which is taken once a day. It should be taken at approximately the same time each day.

Possible side effects

Each person’s reaction to any medication is unique. Most people have very few side effects with anastrozole, while others may experience more. The side effects described in here will not affect everyone and may be different if you are having more than one drug.

We have outlined the most common side effects. However, we have not included those that are very rare and therefore extremely unlikely to affect you. If you notice any effects that are not listed in the section, please discuss them with your doctor or nurse.

You will see your doctor regularly while you have this treatment so that he or she can monitor the effects. This section should help you to discuss any queries about your treatment and its side effects with your doctor or nurse, as they are in the best position to help and advise you.

Some people may have the following side effects to varying degrees.

Hot flushes and sweats  These are usually mild and may wear off after a period of time. Sometimes women find that avoiding or cutting down on tea, coffee, nicotine and alcohol can reduce sweats. Recent research suggests that progesterone or some anti-depressants may be helpful in controlling this side effect. Some women find that complementary therapies help, and your GP may be able to give you details about obtaining these on the NHS.

If you are having troublesome hot flushes, discuss these with your doctor.

Vaginal dryness  This may occur while using anastrozole. Gels are available which can help to overcome the dryness. The gels are available from any chemist or can be prescribed by your doctor. CancerBACUP’s section on sexuality and cancer contains more information about how to cope with this effect.

Nausea (feeling sick), vomiting and diarrhoea  These side effects are uncommon. If they do occur they can usually be effectively treated, so let your doctor know. Feelings of sickness can often be relieved by taking your tablet with food or at night. If you have diarrhoea it is important to drink plenty of fluids.

Hair thinning  Some women notice that their hair becomes thinner while taking anastrozole. This is usually mild and the hair goes back to normal at the end of treatment.

Headaches  Some people have headaches whilst taking anastrozole but this is not common. It is important to drink plenty of fluids. Let your doctor know if you are getting headaches as medication can be prescribed.

Skin rashes  Rarely, anastrozole can cause skin rashes.

Vaginal bleeding  Vaginal bleeding (usually in the first few weeks of treatment) has been reported. This is rare and has usually occurred after changing from other hormonal therapies to treatment with anastrozole. If the bleeding continues, tell your doctor or breast care nurse.

Joint pains/stiffness  This side effect is uncommon but some women have pain and stiffness in their joints while taking anastrozole. Let your doctor know if these effects are troublesome. It may be helpful to take mild painkillers.

Tiredness and lethargy  Some people can experience increased tiredness, especially at the start of treatment. It is important to get plenty of rest. If you are very sleepy you should take extra care when driving or operating hazardous machinery.

Length of treatment

Anastrazole may be given over a period of months or a number of years depending on your individual situation. Your doctors will discuss the length of treatment that they feel is appropriate for you.

Things to remember about anastrozole tablets

  • Keep the tablets in a safe place where children cannot reach them, as anastrozole could harm them.
  • If your doctor decides to stop the treatment, return any remaining tablets to the pharmacist. Do not flush them down the toilet or throw them away.
  • If you are sick just after taking the tablet tell your doctor or nurse as you may need to take another one.
  • If you forget to take your tablet, don’t worry. The levels of the drug in your blood will not change very much but try not to miss more than one or two tablets in a row. Let your doctor or nurse know.
  • Remember to get a new prescription a few weeks before you run out of tablets and make sure you have plenty for holidays etc.


This section has been compiled using information from a number of reliable sources including;

  • Martindale: The Complete Drug Reference (33rd edition). Sweetman et al. Pharmaceutical Press, 2002.
  • British National Formulary (46th edition). British Medical Association and Royal Pharmaceutical Society of Great Britain, September 2003.

For further references, please see the general bibliography.

Anastrozole (Arimidex®)

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