This page tells you about the hormone therapy anastrozole and its possible side effects. There are sections about
Anastrozole is also called Arimidex. It is a type of hormone therapy called an aromatase inhibitor. Anastrozole treats advanced breast cancer in women who have had their menopause.
Anastrozole lowers the amount of oestrogen in the body. The female sex hormones oestrogen and progesterone stimulate many breast cancers to grow. Lowering the level of oestrogen can stop or slow the growth of breast cancer cells.
Anastrozole blocks a process called aromatisation which changes sex hormones called androgens into oestrogen. This happens mainly in the fatty tissues, muscle and the skin and needs a particular enzyme called aromatase.
You take anastrozole as a tablet, once a day. 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.
It is very important that you take tablets according to the instructions your doctor or pharmacist gives you. You should take the right dose, not more or less. It is a long term treatment and you usually need to take it for several years. Never stop taking a cancer drug without talking to your specialist first.
If you accidentally take more anastrozole than you should, let your doctor know straight away.
If you forget a dose, continue with the next dose as normal. Don't take an extra dose to make up for the missed one.
You have blood tests before starting treatment and regularly during your treatment. The tests check your levels of blood cells and other substances in the blood. They also check how well your liver and kidneys are working.
We've listed the side effects associated with anastrozole. You can use the links to find out more about each side effect. Where there is no link, please go to our information about cancer drug side effects or use the search box at the top of the page.
You might have a few side effects. They may be mild or more severe. A side effect may get better or worse through your course of treatment. Or more side effects may develop as the course goes on. This depends on
- How many times you've had the drug before
- Your general health
- The amount of the drug you have (the dose)
The side effects may be different if you are having anastrozole with other medicines.
Tell your doctor, nurse or pharmacist straight away if any of the side effects get severe.
More than 10 in every 100 people have one or more of these.
- Hot flushes and sweats
- Feeling sick is usually mild and can usually be controlled by anti sickness medicines
- Skin rashes – these are usually mild but let your doctor or nurse know if you have a rash
- Painful or stiff joints happen in more than 3 out of 10 women (30%)
- Swollen joints (arthritis)
- Feeling weak
- Loss of bone strength caused by a lack of oestrogen over a long period of time – the bones are more likely to break. You have a DEXA scan to check your bone density before you start treatment
- Mood changes happen in up to 2 in 10 women (20%)
- Tiredness or fatigue happens in up to 2 out of 10 women (20%)
- A lowered interest in sex (reduced libido) occurs in more than 1 out of 10 women (10%)
Between 1 and 10 in every 100 people have one or more of these.
- Bone pain – your nurse can give you painkillers
- Painful hands with a weakened grip and numbness and tingling – carpal tunnel syndrome
- Hair thinning may happen, but is usually mild
- Loss of appetite
- Raised cholesterol levels in the blood – this is usually only slightly raised and you will have regular blood tests to check it
- Feeling sleepy
- Being sick – you can have medicines to control this
- Liver changes that are very mild and unlikely to cause symptoms – they will usually go back to normal when treatment is finished, but you will have regular blood tests to check how well your liver is working
- Diarrhoea – drink plenty of fluids and tell your doctor or nurse if diarrhoea becomes severe or continues for more than 3 days
- Dryness of the vagina – you can get vaginal moisturisers (lubricants) from your nurse or from the pharmacist
- Vaginal bleeding – this mainly happens in the first few weeks of treatment. Tell your doctor or nurse if the bleeding continues
Fewer than 1 in 100 people have these effects.
- Inflammation of the liver (hepatitis)
- Trigger finger – the finger or thumb is fixed in a bent position. Tel your doctor or nurse if you notice this
Talk to your doctor, pharmacist or nurse about all your side effects so they can help you manage them. They can give you advice or reassure you. Your nurse will give you a contact number to ring if you have any questions or problems. If in doubt, call them.
Tell your doctor about any other medicines you are taking, including vitamins, herbal supplements and over the counter remedies. Some drugs can react together.
Pregnancy and contraception
This drug may harm a baby developing in the womb. It is important not to become pregnant or father a child while you are having treatment with this drug and for a few months afterwards. Talk to your doctor or nurse about effective contraception before starting treatment.
Don't breastfeed during this treatment because the drug might come through in the breast milk.
Anastrozole tablets contain lactose (milk sugar). If you have an intolerance to lactose, contact your doctor before taking this medicine.
This page doesn't list all the very rare side effects of this treatment that are very unlikely to affect you. For further information look at the Electronic Medicines Compendium website at www.medicines.org.uk.
If you have a side effect not mentioned here that you think may be due to this treatment you can report it to the Medicines Health and Regulatory Authority (MHRA) at yellowcard.mhra.gov.uk.
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.
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