What is letrozole?

Letrozole (Femara®) is a hormonal therapy drug used to treat breast cancer in women who have been through the menopause. Sometimes it is used to treat breast cancer in men.

Letrozole may be used:

  • before surgery, to try to reduce the size of the cancer and avoid a mastectomy (removal of the breast)
  • after other treatments, to reduce the risk of breast cancer coming back
  • to control breast cancer that has come back or spread to other parts of the body (secondary breast cancer).

It is best to read this information with our general information about hormonal therapies and the type of cancer you have. 

Your doctor will talk to you about this treatment and its possible side effects before you agree (consent) to have treatment. They will explain why you are having letrozole and how long you will take it for.

How letrozole works

Hormones are chemicals that our bodies make. They act as messengers and help control how cells and organs work. Hormonal therapies are drugs that change 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.

Letrozole reduces the amount of oestrogen in the body. It blocks an enzyme (a type of protein) that helps produce oestrogen in the fatty tissues of the body.

Before a woman goes through the menopause, oestrogen is also made in the ovaries. You may have other types of hormone therapy if you have not been through the menopause.

Taking letrozole tablets

Letrozole comes as tablets you can take at home. You take letrozole once a day, with or without food. Try to take it at the same time each day.

If you forget to take your tablet, take it as soon as you remember. If it is nearly time for the next dose, just take your usual dose the next day. Do not take a double dose.

Letrozole is a long-term treatment. You may need to take it for several years. Your nurse or doctor will talk to you about your treatment plan. Always take the tablets exactly as explained. This is important to make sure they work as well as possible for you.

Other things to remember about your tablets:

  • Keep them in the original package and at room temperature, away from heat and direct sunlight.
  • Keep them safe and out of the sight and reach of children.
  • Get a new prescription before you run out of tablets, and make sure you have enough for holidays.
  • If your treatment is stopped, return any unused tablets to the pharmacist.

About side effects

We explain the most common side effects of this treatment here. We also include some less common side effects.

You may get some of the side effects we mention, but you are unlikely to get all of them. If you are also having treatment with other cancer drugs, you may have some side effects that we have not listed here.

You will see a doctor, nurse or pharmacist regularly while you are having this treatment. Always tell them about any side effects you have. They can give you drugs to help control most side effects. They can also offer advice to help you cope.

Most side effects can be managed. But sometimes side effects are harder to control. It is important not to stop taking hormonal therapy without telling your doctor. If side effects cannot be managed, your doctor may suggest you take a different type of hormonal therapy.

Serious and life-threatening side effects

Some cancer treatments can cause severe side effects. Rarely, these may be life-threatening. Your cancer doctor or nurse can explain the risk of these side effects to you.

Contact the hospital

Your nurse will give you telephone numbers for the hospital. If you feel unwell or need advice, you can call them at any time of the day or night. Save these numbers in your phone or keep them somewhere safe.

More information

We cannot list every side effect for this treatment. There are some rare side effects that are not listed. You can visit the electronic Medicines Compendium (eMC) for more detailed information.

Common side effects

Hot flushes and sweats

Hot flushes are a common side effect of this treatment. During a flush, your neck and face may feel warm and look red. Flushes may last from a few seconds up to 10 minutes. You may have sweats and then feel cold and clammy. Some people feel anxious or irritable during a hot flush.

There are things you can do to try to reduce flushes:

  • Wear clothes made from natural fabrics, such as cotton.
  • Wear layers of clothes that you can remove if you feel hot.
  • Use cotton bed sheets and have layers of bedding that you can remove if you feel hot.
  • Keep room temperatures cool or use a fan.
  • Have cold drinks rather than hot ones. Try to avoid drinks with caffeine in them.

You may have fewer hot flushes and sweats as your body adjusts to hormonal treatment. Or your doctor can prescribe drugs to help. Flushes and sweats usually stop a few months after treatment finishes, but some people continue to have them.

We have more information about coping with hot flushes. Women can read more about coping with hot flushes in our information about managing menopausal symptoms.

Muscle or joint pain

You may get pain in your muscles or joints. If this happens, tell your doctor so they can give you painkillers. Being physically active may help with the pain and keep your joints flexible. Keeping to a healthy weight may help too. Tell your doctor or nurse if the pain does not get better.

Tiredness

Feeling tired is a common side effect. Try to pace yourself and plan your day so you have time to rest. Gentle exercise, like short walks, can give you more energy. If you feel sleepy, do not drive or operate machinery.

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. Tell your doctor or nurse if you have these symptoms. They can prescribe drugs to help.

Raised cholesterol level

This treatment can raise the level of cholesterol (a fatty substance) in the blood. You may have a blood test to check the level of cholesterol. Your doctor may give you medicines to control your cholesterol levels.

Change in appetite

If you do not have much appetite, try eating small meals often. If problems with eating do not get better, talk to your doctor or nurse.

You may find your appetite increases when you are taking letrozole. Eating well and keeping active will help if you have concerns about your weight.

Hair thinning

Your hair may become thinner when you are taking this treatment. This is usually mild. Ask your nurse for advice if you are worried about this.

Skin changes

This treatment may affect your skinIt may cause a rash, which might be itchy. Your doctor or nurse can tell you what to expect. If your skin feels dry, try using an unperfumed moisturising cream every day.

Always tell your doctor or nurse about any changes to your skin. They can give you advice and may prescribe creams or medicines to help. Skin changes usually improve when treatment finishes.

It is very important to contact your doctor straight away if you get a severe skin rash.

Mood changes

You may have some mood changes during this treatment. You may feel low or depressed. Let your doctor or nurse know if you notice any changes.

Headaches

This treatment may cause headaches. If this happens, tell your doctor or nurse. They can give you painkillers.

Feeling dizzy

This treatment may cause dizziness. Tell your doctor or nurse if this is a problem.

Weight gain

You may gain weight when you are having this treatment. Eating healthily and being active can help you keep to a healthy weight. Your doctor, nurse or a dietitian can give you more advice.

Vaginal bleeding or dryness

This treatment can cause vaginal changes. You may have bleeding when you start this treatment, or if you change to it from another treatment. If bleeding continues for more than a few days, tell your doctor or nurse.

You can use non-hormonal creams, gels or lubricants to help with vaginal dryness and any discomfort during sex. You can buy these from a chemist, or your doctor can prescribe them. We have more information about cancer and sex.

Diarrhoea

This is usually mild. If it does not get better, your doctor can prescribe drugs to control it. Make sure you drink at least 2 litres (31/2 pints) of fluids every day if you have diarrhoea.

Constipation

This treatment can cause constipation. Here are some tips that may help:

  • Drink at least 2 litres (3½ pints) of fluids each day.
  • Eat high-fibre foods, such as fruit, vegetables and wholemeal bread.
  • Do regular gentle exercise, like going for short walks.

If you have constipation, contact the hospital for advice. Your doctor can give you drugs called laxatives to help.

Bone thinning (osteoporosis)

If you take this treatment for several months or more, you may get bone thinning. This is called osteoporosis. This can increase your risk of a broken bone (fracture). You may have bone density scans to check your bone health before and during treatment.

Doing regular exercise, such as walking, can improve your bone health. Eating a healthy diet can help too. Your doctor may prescribe drugs called bisphosphonates to help protect your bones. They may also advise you to take calcium and vitamin D supplements.

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.

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.

Less common side effects of letrozole

Effects on the heart

This treatment can affect the way your heart works. Your doctor may do tests to see how well your heart is working. You may have these tests before, during, and sometimes after treatment.

Contact a doctor straight away if you:

  • have pain or tightness in your chest
  • feel breathless or dizzy
  • feel your heart is beating too fast or too slowly.

Other conditions can cause these symptoms. But it is important to get them checked by a doctor.

Other information

Blood clot risk

Cancer and some cancer treatments can increase the risk of a blood clot. Symptoms of a blood clot include:

  • pain, redness or swelling in a leg or arm
  • breathlessness
  • chest pain.

If you have any of these symptoms, contact a doctor straight away.

A blood clot is serious, but can be treated with drugs that thin the blood. Your doctor or nurse can give you more information.

Other medicines

Some medicines can affect how this treatment works or be harmful when you are having it. Always tell your cancer doctor about any drugs you are taking or planning to take, such as:

  • medicines you have been prescribed
  • medicines you buy in a shop or chemist
  • vitamins, herbal drugs and complementary therapies.

Tell other doctors, pharmacists or dentists who prescribe or give you medicines that you are having this cancer treatment.

You can visit the electronic Medicines Compendium (eMC) for more detailed information about your treatment.

Medical and dental treatment

If you need medical treatment for any reason other than cancer, always tell the doctors and nurses that you are having cancer treatment. Give them the contact details for your cancer doctor so they can ask for advice.

If you think you need dental treatment, talk to your cancer doctor or nurse. Always tell your dentist you are having cancer treatment.

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