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Anastrozole - Brand name: Arimidex

On this page

  1. About anastrozole
  2. Key facts
  3. Who can and cannot take anastrozole
  4. How and when to take anastrozole
  5. Side effects
  6. How to cope with the side effects of anastrozole
  7. Pregnancy and breastfeeding
  8. Cautions with other medicines
  9. Common questions about anastrozole

1. About anastrozole

Anastrozole is a type of hormone treatment. It works by lowering the levels of oestrogen hormones in your body.

It is mainly prescribed for women who have been through the menopause and have a type of cancer called hormone-dependent breast cancer. It can sometimes also be used:

  • to prevent breast cancer if you are high risk and have been through the menopause
  • to treat breast cancer in men
  • to treat breast cancer in younger women before the menopause
  • as a fertility treatment if you have polycystic ovary syndrome

Most people who take anastrozole will have had surgery, radiotherapy or sometimes chemotherapy to treat their breast cancer first.

Anastrozole is available on prescription only. It comes as tablets.

2. Key facts

  • You usually take anastrozole once a day. Try to take it at the same time each day, as this makes it easier to remember.
  • Treatment with anastrozole usually lasts for up to 5 years. It is important to complete your course of treatment.
  • Common side effects can be like menopause symptoms and include hot flushes, difficulty sleeping, tiredness and low mood.
  • Side effects usually improve after a few months as your body gets used to the medicine.
  • Your doctor will monitor your blood pressure, cholesterol levels and bone density during your treatment.

3. Who can and cannot take anastrozole

Anastrozole is not suitable for some people. Tell your doctor before starting on this medicine if you:

  • have had an allergic reaction to anastrozole or any other medicines in the past
  • still have periods
  • are pregnant, trying to get pregnant or breastfeeding
  • have serious kidney or liver disease
  • have been told you have fragile or brittle bones (osteoporosis)

4. How and when to take anastrozole

Swallow the tablet whole with a drink of water. Do not crush or chew it.

You can take anastrozole with or without food.


Anastrozole comes as 1mg tablets. The usual dose is 1 tablet, taken once a day.

Try to take your anastrozole at the same time each day, this will make it easier to remember. You can choose a time that suits your everyday routine

What if I forget to take it?

If you forget to take your medicine, just skip the missed dose. Take your next dose at the normal time.

Do not take a double dose to make up for a forgotten one. If you forget doses often, it may help to set an alarm to remind you. You could also ask your pharmacist for advice on other ways to help you remember to take your medicine.

What if I take too much?

If you take too many anastrozole tablets, you may get symptoms like feeling sick, vomiting or diarrhoea.

Urgent advice: Contact 111 for advice now if:

  • you take too many tablets and feel unwell

Call 111 or go to

5. Side effects

Like all medicines, anastrozole can cause side effects, although not everyone gets them.

Anastrozole may affect your blood pressure, cholesterol and bone density. Your doctor will monitor this carefully and can recommend additional treatment if needed.

Common side effects

Menopause symptoms usually improve during the first few months of taking anastrozole.

These common side effects happen in more than 1 in 100 people.

  • hot flushes and sweating
  • dry or itchy vagina and genitals, bleeding from your vagina
  • difficulty sleeping
  • feeling very tired
  • feeling or being sick, loss of appetite
  • mild aches in your muscles and bones
  • numb or tingling hands
  • changes to your skin, including a mild rash
  • hair loss or thinning hair
  • low mood or depression

Talk to your doctor or a pharmacist if these side effects bother you or do not go away:

Serious side effects

Serious side effects are rare and happen in less than 1 in 100 people.

Tell a doctor if:

  • your muscles feel weak, or the joints or tendons in your ankles, legs, shoulders or arms feel weak, painful or swollen
  • your skin or the whites of your eyes turn yellow – this can be a sign of liver problems
  • your eyesight becomes blurry
  • you’re feeling thirsty and peeing a lot, feeling sick and have lost your appetite – you may need a blood test to check your calcium levels
  • you get red or purple spots (if you have light skin) or dark spots (if you have darker skin), painful joints, stomach ache, or pain in your side (below your ribs), lower back or around your genitals – these can be signs of Henoch-Schönlein purpura (HSP), a condition affecting your blood vessels

Immediate action required: Call 999 or go to A&E if:

  • you have sudden weakness or loss of feeling in any part of your body
  • your face drops on one side
  • you have difficulty speaking
  • you get a very sudden and severe chest pain

Face dropping and difficulty speaking can be signs of a stroke, and sudden severe chest pain can be a sign of a heart attack.

Serious allergic reaction

In rare cases, it's possible to have a serious allergic reaction (anaphylaxis) to anastrozole.

Immediate action required: Call 999 now if:
  • your lips, mouth, throat or tongue suddenly become swollen
  • you're breathing very fast or struggling to breathe (you may become very wheezy or feel like you're choking or gasping for air)
  • your throat feels tight or you're struggling to swallow
  • your skin, tongue or lips turn blue, grey or pale (if you have black or brown skin, this may be easier to see on the palms of your hands or soles of your feet)
  • you suddenly become very confused, drowsy or dizzy
  • someone faints and cannot be woken up
  • a child is limp, floppy or not responding like they normally do (their head may fall to the side, backwards or forwards, or they may find it difficult to lift their head or focus on your face)

You or the person who's unwell may also have a rash that's swollen, raised, itchy, blistered or peeling.

These can be signs of a serious allergic reaction and may need immediate treatment in hospital.

These are not all the side effects of anastrozole. For a full list, see the leaflet inside your medicines packet.


You can report any suspected side effect using the Yellow Card safety scheme.

Visit Yellow Card for further information.

6. How to cope with the side effects of anastrozole

Menopause symptoms such as hot flushes, difficulty sleeping, tiredness and low mood usually improve during the first months of taking anastrozole. However, if they are severe or last longer than a few months, talk to your doctor or breast cancer nurse.

What to do about:

  • hot flushes and sweating – try cutting down on spicy food, caffeine, smoking and alcohol. It may help to keep the room cool and use a fan. Try spraying your face with cool water, or sipping a cold drink.
  • dry or itchy vagina, bleeding from your vagina – ask your doctor or breast cancer nurse to recommend a vaginal moisturiser for treating irritation or dryness. Vaginal bleeding usually happens in the first few weeks after starting anastrozole. Talk to your doctor if it lasts longer than a few days. Also talk to your doctor if these symptoms first appear more than a few weeks after you start taking anastrozole.
  • difficulty sleeping – avoid caffeine (tea, coffee, cola and chocolate) in the afternoon and evening. Keep your bedroom dark and quiet, and try going to bed and getting up at a set time each day. It may also help to stop watching TV, looking at your mobile phone or using other electronic devices (like tablets), at least 1 hour before bedtime.
  • feeling very tired – gentle exercise and eating healthily can help make you feel less tired. Try going to bed and getting up at a set time each day. Do not drive, ride a bike or operate machinery if you feel very tired while taking anastrozole. This will usually start to improve as your body gets used to the medicine. Speak to your doctor if it does not get better.
  • feeling or being sick, loss of appetite – it might help to take anastrozole after you've eaten. Choose foods you normally enjoy but avoid rich or spicy food. Try eating smaller meals but more often. If you're being sick, have small, frequent sips of water to avoid dehydration. Talk to your doctor if your symptoms do not improve or get worse.
  • mild aches in your muscles or bones – ask a pharmacist to recommend a suitable painkiller. If the pain lasts more than a week, ask your doctor for advice. If you have a sudden attack of pain in a joint ask a doctor for advice urgently.
  • numb or tingling hands – stop taking the medicine and ask your doctor for advice
  • changes to your skin, including a mild rash – it may help to take an antihistamine. You can buy these at a pharmacy without a prescription. Check with a pharmacist to see what's suitable for you.
  • hair loss or thinning hair – some people find that their hair gets thinner when they start taking anastrozole. This is usually mild. Ask your breast cancer nurse for advice if this is bothering you.
  • low mood or depression – it is difficult to know whether this is due to the medicine or a response to menopausal symptoms or being diagnosed with cancer. Speak to your doctor or specialist nurse. They may recommend therapies, like cognitive therapy and mindfulness, or antidepressant medicines.

7. Pregnancy and breastfeeding

Anastrozole is not recommended when pregnant or breastfeeding, because it interferes with hormone levels in you and your baby. And there is not enough information available to say if it's safe.

Talk to your doctor straight away if there is any chance that you could be pregnant.

Non-urgent advice: Tell your doctor if you're:

  • trying to get pregnant
  • pregnant
  • breastfeeding

8. Cautions with other medicines

There are very few medicines that affect the way anastrozole works in the body.

However, do not take hormone replacement therapy (HRT) or any other medicines that relieve menopausal symptoms. These may contain ingredients similar to the hormone oestrogen and could stop anastrozole working as well as it should in treating your cancer.

Mixing anastrozole with herbal remedies and supplements

Do not take any herbal remedies or supplements for menopausal symptoms while taking anastrozole. These can stop anastrozole working as well as it should.

There is very little information about taking other herbal remedies and supplements together with anastrozole.

Important: Medicine safety

Tell your doctor or pharmacist if you're taking any other medicines, including herbal medicines, vitamins or supplements.

9. Common questions about anastrozole

How does anastrozole work?

Anastrozole belongs to a group of medicines called aromatase inhibitors.

Aromatase inhibitor medicines are used to treat certain types of breast cancer, where the cancer cells need oestrogen (a hormone) to grow.

After the menopause your ovaries stop producing oestrogen. Instead your body makes oestrogen from an enzyme called aromatase.

Aromatase inhibitors reduce the amount of aromatase in your body and this in turn stops your body producing oestrogen. This helps prevent cancer cells growing, as they no longer have anything to feed on.

What are the benefits of taking anastrozole?

Anastrozole helps stop your breast cancer coming back after having treatment for cancer.

By taking this medicine for 5 years, you have a better chance of being alive 15 years after your breast cancer was first diagnosed.

Your specialist will be able to explain the benefits and risks of taking anastrozole.

They can also calculate how well anastrozole is likely to work for you. This is done by comparing your details with those of more than 20,000 other people who have had treatment for breast cancer.

The exact benefits and how well it’s likely to work for you depend on a combination of different things.

This varies for each person and includes factors like your age when the breast cancer was found, how it was found and whether you’ve had chemotherapy or not.

How long does it take to work?

Anastrozole will immediately start to reduce the amount of oestrogen in your body. However, it takes several weeks or months for the medicine to work fully.

During this time you’re likely to have menopause symptoms as your body gets used to having less oestrogen. These symptoms will gradually improve as your body adjusts to the medicine.

How long will I take it for?

Most people who take anastrozole will have had surgery, radiotherapy or sometimes chemotherapy to treat their breast cancer first.

In this case, surgery, radiotherapy or chemotherapy is the first (primary) treatment and anastrozole is an additional (adjuvant) therapy. Adjuvant therapy helps stop the cancer coming back.

Most people will have adjuvant therapy for 5 years. However sometimes your doctor will advise continuing it for longer. During this time you may be given anastrozole only, or tamoxifen (a drug that can also be used to treat breast cancer) for a few years followed by anastrozole for the remaining time.

Anastrozole is sometimes used to treat cancer if you cannot have surgery, or to shrink the cancer before surgery if you cannot have chemotherapy. In this case your specialist will tell you how long to take the medicine for.

Is it safe to take for a long time?

Anastrozole is generally safe to take long term, however your specialist team will monitor your health carefully.

This is because anastrozole reduces levels of oestrogen that your body needs for strong and healthy bones. If you take anastrozole for a long time your bones can become weaker (osteoporosis) and more likely to break.

You will have bone density scans before you start taking anastrozole, 1 or 2 years into treatment and again after you finish your treatment.

Your doctor may recommend a type of medicine called a bisphosphonate to help reduce bone damage. They can also give you advice on exercise and diet to help keep your bones strong.

Anastrozole can also increase your blood pressure and cholesterol levels. Your doctor will monitor these during your regular check-ups and recommend treatment as needed.

Can I stop taking it?

If you want to stop taking it for any reason, your doctor will be able to discuss alternatives for treating your breast cancer or preventing it coming back.

Sometimes people may have a short break from anastrozole. This can help if you are getting side effects such as joint pain. However, only take a break from your medicine if you have discussed it with your doctor first and they agree to it.


Do not stop taking anastrozole without talking to your doctor first.

Are there other medicines like anastrozole?

Medicines such as tamoxifen, letrozole and exemestane work in a similar way to anastrozole. These medicines lower your oestrogen levels and can cause similar side effects.

However, medicines affect people in different ways. If you are bothered by side effects from taking anastrozole, talk to your doctor. They may recommend one of these other medicines instead.

Can I drink alcohol with it?

There is no evidence that drinking alcohol causes any problems when taking anastrozole.

Some people taking anastrozole may get hot flushes or redness when they drink alcohol. In this case, avoiding alcohol may help.

Is there any food or drink I need to avoid?

Most people can eat and drink normally when taking anastrozole. Although some people may get hot flushes or redness when they drink alcohol.

Some people find anastrozole affects their appetite.

If you lose your appetite, try to make sure you have a balanced diet by eating smaller meals and more often.

If it makes you feel hungrier and you’re putting on a lot of weight, ask your doctor or specialist nurse to refer you to a dietitian.

Will it affect my contraception or fertility?

Anastrozole is generally only given to you if you have gone through the menopause.

However, some people find that they start to having periods again after taking anastrozole. If this happens to you, it’s important to use reliable contraception. Talk to your doctor if your periods start again, or if there is any chance that you maybe are pregnant.

Anastrozole is not recommended during pregnancy .

Can I drive or ride a bike?

Some people feel extremely tired when taking anastrozole.

If you feel tired or dizzy, or if you get blurred vision, do not drive, cycle or use tools or machinery until you feel OK again.

Page last reviewed: 2 June 2021
Next review due: 2 June 2024