Letrozole (Femara ®)
Letrozole is a hormonal therapy drug. It is 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.
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. Letrozole is a drug called an aromatase inhibitor. It blocks this process and reduces the amount of oestrogen in the body.
When letrozole is given
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Letrozole is used after surgery and other treatments to reduce the risk of 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 drug.
Sometimes doctors give letrozole before surgery to try to reduce the size of the cancer and avoid having a mastectomy (removal of the breast). Letrozole is also used to control breast cancer that has spread to other parts of the body (secondary breast cancer).
Taking your letrozole tablets
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You take letrozole 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 remaining tablets to the pharmacist if your treatment is stopped.
Possible side effects of letrozole
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We explain the most common side effects of letrozole 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 having 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 some of them and give you advice about managing them. Don’t stop taking letrozole unless your doctor advises you to.
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, like hot flushes, in our section on breast cancer and menopausal symptoms.
Taking letrozole for a few years increases your risk of bone thinning, called osteoporosis. This can increase your risk of a broken bone (fracture). You will usually have a bone density scan 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 to strengthen your bones.
Tiredness and lack of energy
You may feel tired, sleepy or feel like you have no energy when you start taking letrozole. Try to pace yourself until this improves. It’s important to get the right balance of having enough rest and being physically active. Regular short walks will help you to feel less tired. If you feel sleepy, don’t drive or operate machinery.
Joint and muscle pain
You may have pain and stiffness in your joints, and sometimes in your muscles, while taking letrozole. Let your doctor or nurse know if this happens. They can prescribe painkillers and give you advice. Being physically active and maintaining a healthy weight can help reduce joint pain and keep them flexible. Let your doctor know if it doesn’t get better.
Feeling sick and indigestion or tummy pain
Any sickness is usually mild, but let your doctor or nurse know if this happens. Letrozole may also cause indigestion or tummy pain. Let them know if you have any of these symptoms. They can prescribe drugs to help.
Change in appetite
If you don’t have much appetite, try eating small meals often and regularly. If problems with eating don’t get better talk to your doctor or nurse.
Some women find their appetite increases. Eating healthily and being physically active will help if you have concerns about your weight.
Some women notice that their hair becomes thinner while taking letrozole. This is usually mild. Your hair will get thicker after treatment finishes.
You may get a mild skin rash. Tell your doctor or nurse if this happens. It’s very important to contact your doctor straightaway if you get a severe skin rash.
Mood and behaviour changes
Some women may find they have a low mood while taking letrozole. Or you may have problems concentrating, feel anxious or have difficulty sleeping. Talk to your nurse or doctor if you have these changes so they can give you support and advice.
If you have headaches let your doctor or nurse know. They can usually be controlled with painkillers you can buy yourself.
Letrozole may cause dizziness. Let your doctor or nurse know if this is a problem.
You may put on weight when you’re taking hormonal therapy. Eating healthily and being more physically active can help to keep you to a healthy weight. Your nurse can give you more advice.
Rarely women can cause vaginal bleeding. If this happens it is most likely in the first few weeks of treatment, or when you change from another hormonal therapy to letrozole. If bleeding continues for more than a few days, tell your doctor or nurse.
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.
Build-up of fluid
You may get swollen feet and ankles because of fluid building up. If you notice this or any other swelling let your doctor know.
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.
Less common side effects
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Non-hormonal creams and gels or lubricants can help reduce dryness and discomfort during sex. You can buy these at a chemist or your doctor can prescribe them.
Let your doctor know if you have pain or discomfort when you pass urine, or if you need to go more often, or your urine is cloudy or smelly. Drink lots of fluids if you think you may have an infection.
Occasionally women get sore eyes or blurry vision with letrozole. Always tell your doctor or nurse if you notice any change in your vision.
Changes to your heartbeat
If you notice changes to your heartbeat, such as it speeding up, let your doctor know. If you have pain or tightness in your chest, or feel breathless at any time during or after treatment, see a doctor straightaway.
Other information about letrozole
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If you have ongoing problems
Most of the time side effects settle within a few months of starting letrozole, 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, get back to your doctor or nurse. They may suggest you try something else.
It’s really important not to stop taking letrozole 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.
Letrozole 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 and herbal drugs.
Medical and 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 letrozole. Explain you are taking hormonal therapy that no one should stop or restart without checking with your cancer doctor first. Give them contact details for your cancer doctor so they can ask for advice.
Always tell your dentist you are taking letrozole.
The information in this section has been produced in accordance with the following sources 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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