Anastrozole (Arimidex ®)
This information is about a hormonal therapy drug called anastrozole. It's used to treat breast cancer in women who have been through the menopause.
It’s best to read this information with our general information about breast cancer or secondary breast cancer in women. We also have information about breast cancer in men, which explains the hormonal therapies used in men.
Hormones are substances produced naturally in the body. They act as chemical messengers and help control the activity of cells and organs. Hormonal therapies interfere with the way hormones are made or how they work in the body.
Many breast cancers rely on the hormone oestrogen to grow. This type of breast cancer is called oestrogen receptor-positive (ER positive) breast cancer.
After the menopause, oestrogen is no longer made in the ovaries. Instead, it’s made in the fatty tissues of the body. This happens when an enzyme called aromatase changes other hormones into oestrogen. Anastrozole is a drug called an aromatase inhibitor. It blocks this process and reduces the amount of oestrogen in the body.
When anastrozole is given
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Anastrozole is used after surgery and other treatments to reduce the risk of early breast cancer coming back. You will usually take it for a few years. Doctors sometimes prescribe it before or after you have another type of hormonal therapy.
Anastrozole is also used to control breast cancer that has spread to other parts of the body (secondary breast cancer).
Your doctor or nurse will explain how long you should take anastrozole for.
Taking your anastrozole tablets
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You take anastrozole as a tablet once a day. You take it at the same time each day, morning or evening. Always take your tablets exactly as your nurse or pharmacist explained. This is important to make sure they work as well as possible for you.
There are some important things to remember when taking your tablets:
If you forget to take your tablet, take one as soon as you remember. This is unless it’s nearly time for your next one - don’t take a double dose.
Keep tablets in the original package and at room temperature, away from heat and direct sunlight.
Keep them safe and out of the reach of children.
Get a new prescription before you run out of tablets and make sure you have plenty for holidays.
Return any unused tablets to the pharmacist if your treatment is stopped.
Possible side effects of anastrozole
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We explain the most common side effects of anastrozole here. But we don’t include all the rare ones that are unlikely to affect you. You may get some of the side effects we mention, but you are very unlikely to get all of them. If you are taking other drugs as well, you may have some side effects that we don’t list here.
Always tell your doctor or nurse about the side effects you have. They can prescribe drugs to help control them and give you advice about managing them. Don’t stop taking anastrozole without talking to your doctor first.
Hot flushes and sweats
These are common and are often mild, but this can vary. Hot flushes and sweats may lessen after the first few months. Cutting down on nicotine, alcohol and hot drinks containing caffeine, such as tea and coffee, can help. Dress in layers, so you can remove clothes as needed. Natural fabrics, such as cotton, may feel more comfortable.
If hot flushes are troublesome, tell your doctor. Low doses of certain antidepressant drugs can help to reduce flushes.
You can read more about treatments for menopausal symptoms, such as hot flushes, in our section on breast cancer and menopausal symptoms.
Taking anastrozole for a few years increases your risk of bone thinning, which is called osteoporosis. This can increase your risk of a broken bone (fracture). You will usually have bone density scans to check your bone health before and during treatment. If you are at risk of osteoporosis, your doctor may prescribe drugs called bisphosphonates to protect your bones. They will also usually advise you to take calcium and vitamin D supplements. Regular walking, eating a healthy diet, not smoking and sticking to sensible drinking guidelines will also help strengthen your bones.
Joint and muscle pain
You may have pain and stiffness in your joints, and sometimes in your muscles, while taking anastrozole. Tell your doctor or nurse if this happens. They can prescribe painkillers and give you advice. Being physically active and keeping to a healthy weight can help reduce joint pain and keep them flexible. Let your doctor know if it doesn’t get better.
Non-hormonal creams, gels or lubricants can help to reduce vaginal dryness and discomfort during sex. You can buy these at a chemist or your doctor can prescribe them.
Tiredness and lack of energy
You may feel tired, sleepy or like you have no energy when you start taking anastrozole. Try to pace yourself until this improves. It’s important to get the right balance of having enough rest and being physically active. Going for regular short walks will help you to feel less tired. If you feel sleepy, don’t drive or use machinery.
This is usually mild. If it doesn’t get better, your doctor can prescribe drugs to control it. Make sure you drink at least two litres (three and a half pints) of fluid every day if you have diarrhoea.
Feeling or being sick, and having no appetite
Any sickness is usually mild, but let your doctor or nurse know if this happens. Try taking your anastrozole tablets with food or at night. If you don’t have an appetite, try to eat lots of small meals or snacks regularly.
If you have headaches, let your doctor or nurse know. They can usually be controlled with painkillers you can buy yourself.
You may get a mild skin rash. Tell your doctor or nurse if this happens. It’s very important to contact your doctor straight away if you get a severe rash.
Some women notice that their hair becomes thinner while taking anastrozole. Your hair will get thicker after treatment finishes.
Rarely, anastrozole can cause vaginal bleeding. If this happens, it’s usually in the first few weeks of treatment or when you change from another hormonal therapy to anastrozole. If bleeding continues for more than a few days, tell your doctor or nurse.
Changes in mood and concentration
Some women have mood changes or problems with concentration, similar to those you get with the menopause. Talk to your nurse or doctor if this is a problem for you.
You may put on weight when you’re taking hormonal therapy. Eating healthily and being more physically active can help you keep to a healthy weight. Your nurse can give you more advice.
Less common side effects of anastrozole
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Pain, numbness and tingling in hand and fingers
These symptoms may be due to carpal tunnel syndrome, which is caused by pressure on a nerve in the wrist. It’s more common in women taking anastrozole. Tell your doctor if you have these symptoms.
Raised blood pressure
Tell your doctor or nurse if you have ever had any problems with your blood pressure. Your nurse will check it regularly during your treatment.
Raised cholesterol level
Your doctor may check your cholesterol levels with a blood test.
Side effects can usually be controlled or improved. Always let your doctor or nurse know about any side effects you have so they can help you feel better.
Other information about anastrozole
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If you have ongoing problems
Most of the time side effects settle within a few months of starting anastrozole, or they can be controlled or managed. But for a few women, they can be more troublesome. If this happens, make sure you talk to your cancer doctor or nurse. They can usually suggest ways to improve your side effects. If things don’t improve, go back to your doctor or nurse. They may suggest you try something else.
It’s really important not to stop taking anastrozole without telling your doctor, as this may affect the success of your treatment. If side effects are very troublesome and can’t be managed, your cancer doctor may suggest you take a different type of hormonal therapy.
Anastrozole can interact with other drugs. This includes medicines you can buy in a shop or chemist. Tell your doctor about any medicines you are taking. These include ones you can buy yourself, complementary therapies, vitamins and herbal drugs.
Medical or dental treatment
If you need to go into hospital for any reason other than cancer, always tell the doctors and nurses that you are taking anastrozole. Explain you are taking hormonal therapy and that no one should stop or restart without checking with your cancer doctor first. Tell them the name of your cancer doctor so they can ask for advice.
Always tell your dentist you are taking anastrozole.
This information has been produced in accordance with the following source and guidelines:
electronic Medicines Compendium (eMC). www.medicines.org.uk (accessed May 2014).
Sweetman, et al. Martindale: The Complete Drug Reference. 37th edition. 2011. Pharmaceutical Press.
If you’d like further information on the sources we use, please feel free to contact us.
With thanks to Kavita Kantilal, E-Prescribing Pharmacist who reviewed this information.
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