Anastrozole (Arimidex)

Anastrozole is a type of hormone therapy and is also known by its brand name Arimidex.

It is a treatment for breast cancer that is hormone sensitive. And in women that no longer have their periods (post menopausal).

Anastrozole for men

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.

How anastrozole works

Oestrogen is a female sex hormone that is mainly made in the body’s fatty tissues after the menopause. Oestrogen encourages some breast cancers to grow.

Anastrozole works by lowering the level of oestrogen in the body. This can stop or slow the growth of breast cancer cells.

How you have it

You have anastrozole as tablets.

Try to take it at the same time each day. Swallow the tablet whole with a drink of water. You can take it before, with, or after food.

Taking tablets

You must take tablets and capsules 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 have missed a dose.

When you have anastrozole

The usual amount is one tablet a day. Anastrozole is a long term treatment and you usually take it for up to 5 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.

Side effects

How often and how severe the side effects are 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

Each of these 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

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

Feeling sick 

Talk to the team looking after you about this. 

Skin rash

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

Painful or stiff joints

You might feel some pain from your muscles and joints. Speak to your doctor or nurse about what painkillers you can take to help with this.

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.

Loss of bone strength

Talk to the team looking after you about this. 

Occasional side effects

Each of these 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
  • being sick
  • carpal tunnel syndrome- this can cause tingling, pain, feeling cold and weakness in part of the hand
  • loss of appetite
  • raised cholesterol in the blood
  • feeling sleepy
  • bone and muscle pain
  • sensation changes - your skin might feel tingly or numb
  • you might have little or no taste while on this drug

Rare side effects

Each of these 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
  • 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

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 some other medicines and herbal products. Tell your doctor or pharmacist about any medicines you are taking. This includes vitamins, herbal supplements and over the counter remedies.

Pregnancy and contraception

This treatment might harm a baby developing in the womb. It is important not to become pregnant or father a child while you're having treatment and for a few months afterwards.

Talk to your doctor or nurse about effective contraception before starting treatment. Let them know straight away if you or your partner falls pregnant while having treatment.


Don’t breastfeed during this treatment because the drug may come through into your breast milk.

Treatment for other conditions

Always tell other doctors, nurses, pharmacists or dentists that you’re having this treatment. For example, if you need treatment for anything else, including teeth problems.


This drug contains lactose (milk sugar). If you have an intolerance to lactose, contact your doctor before taking this medicine.

More information about this treatment

For further information about this treatment go to the electronic Medicines Compendium (eMC) 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