Letrozole (Femara®)

Letrozole is a hormonal therapy drug used to treat breast cancer. It is best to read this information with our general information about hormonal therapies and the type of cancer you have.

Letrozole is usually given as tablets. You usually have it as an outpatient. Your cancer doctor, nurse or pharmacist will tell you how often you will have it.

Like all cancer drugs, letrozole can cause side effects. Some of the side effects can be serious, so it is important to read the detailed information below.

Your healthcare team can give you advice on how to manage any side effects. Tell your doctor or nurse straight away if you feel unwell or have severe side effects, including any we do not mention here.

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

If you need medical attention for any reason other than cancer, always tell the healthcare staff that you are having this treatment.

What is letrozole?

Letrozole is a hormonal therapy drug used to treat breast cancer. It can be given alone or with other types of treatment. 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.


How letrozole works

Hormones are chemicals that our bodies make. Hormones 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 a hormone called 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 is made in the fatty tissues of the body. This happens when an enzyme (a type of protein) called aromatase changes other hormones into oestrogen.

Letrozole is a type of drug called an aromatase inhibitor. It blocks (inhibits) the activity of aromatase. It also reduces the amount of oestrogen in the body.


When letrozole is given

Letrozole is used to treat breast cancer in women. You may have it after other treatments, to reduce the risk of breast cancer coming back. Sometimes doctors give letrozole before surgery. This is to try and reduce the size of the cancer and avoid having to remove the breast (mastectomy).

Letrozole is often used in women who have been through the menopause. But it may also be given to women who have not had the menopause. In this situation, you usually have letrozole with a drug that stops the ovaries making oestrogen, or with surgery to remove the ovaries.

Letrozole may also be given along with the targeted therapy drugs ribociclib and palbociclib when breast cancer has spread to other parts of the body (secondary breast cancer).

Letrozole is also sometimes used to treat breast cancer in men.

Your doctor or nurse will explain why you are having letrozole and how long you will take it for.


Taking your letrozole tablets

Letrozole comes as tablets you can take at home. You may have letrozole on its own, or with other drugs. 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. Make sure you:

  • swallow them whole with a glass of water
  • do not chew or crush the tablets
  • take them at the same time every day.

If you forget to take the tablets, you should take the missed dose as soon as possible within the same day. If a full day has passed, let your doctor or nurse know. Do not take a double dose unless your doctor tells you to.

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 reach of children.
  • If you are sick just after taking the tablets, contact your healthcare team. Do not take another dose.
  • Get a new prescription before you run out of tablets, and make sure you have plenty for holidays.
  • If your treatment is stopped, return any unused tablets to the pharmacist.

Your nurse or pharmacist may also give you other medicines to take home. Take all your medicines exactly as they have been explained to you. Do not stop taking any of your medicines unless your doctor tells you to.


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 haven’t listed here. Always tell your doctor, nurse or pharmacist about any side effects you have.

Your doctor can give you drugs to help control some side effects. It is important to take them exactly as your nurse or pharmacist explains. This means they will be more likely to work for you. Your nurse will give you advice about managing your side effects. After your treatment is over, most side effects start to improve.

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

These are common. During a flush, your neck and face may feel warm and look red. Flushes can last for a few seconds or for up to 10 minutes. You may have sweats 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.
  • Dress in layers of clothes that you can remove as needed.
  • Use cotton sheets and have layers of bedding.
  • Keep the room temperature 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. Some people continue to have flushes and sweats, but they usually stop a few months after treatment finishes.

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

Bone thinning (osteoporosis)

Taking this treatment for several months or more can cause 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.

Keeping physically active and eating a healthy diet helps look after your bones. Your doctor may prescribe drugs called bisphosphonates to help protect your bones. They may also advise you to take calcium and vitamin D supplements.

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.

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 and keeping to a healthy weight may help with the pain. It will also keep your joints flexible. Let your doctor or nurse know if it does not get better.

Feeling sick

Any sickness is usually mild. But let your doctor or nurse know if this happens. Try taking your letrozole tablets with food or at night.

Indigestion or tummy pain

Letrozole may also cause indigestion or tummy pain. Let your doctor or nurse know if you have any of these symptoms. They can prescribe drugs to help.

Loss of appetite

Try to eat small, frequent meals or snacks instead of 3 meals a day. This may be helpful if you have lost your appetite or find it difficult to eat big meals.

Hair thinning

Your hair may become thinner while taking this treatment. This is usually mild. Ask your nurse for advice if this is a problem for you.

Skin changes

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

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

Mood and behaviour changes

Some people 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.

Headaches

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

Feeling dizzy

Letrozole may cause dizziness. Let your doctor or nurse know if this is a problem.

Weight gain

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

Vaginal bleeding or dryness

This treatment can cause vaginal bleeding or dryness. Bleeding may happen when you start taking anastrozole or 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.

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

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

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.

Breast cancer and the menopause

Diane describes living with breast cancer and the menopausal symptoms that were caused by her chemotherapy.

About our cancer information videos

Breast cancer and the menopause

Diane describes living with breast cancer and the menopausal symptoms that were caused by her chemotherapy.

About our cancer information videos


Less common side effects of letrozole

Urine infection

Let your doctor know if you have any symptoms of a urine infection. This may include:

  • pain or discomfort when you pee
  • needing to pee more often
  • cloudy or smelly pee.

If you think you may have a urine infection, drink lots of fluids.

Eye problems

Some people get sore eyes or blurry vision when taking letrozole. Always tell your doctor or nurse if you notice any change in your vision.

Effects on the heart

This treatment can affect the way the heart works. You may have tests to see how well your heart is working. These may be done before, during, and sometimes after treatment. If the treatment is causing heart problems, your doctor can change the type of treatment you are having.

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.

Fertility

Some cancer drugs can affect whether you can get pregnant or father a child. If you are a woman, your periods may become irregular or stop. This may be temporary, but for some women it is permanent. Your [menopause] may start sooner than it would have done

There may be ways to preserve fertility for men and women. If you are worried about fertility, it is important to talk with your doctor before you start chemotherapy treatment.

Contraception

Your doctor will advise you not to get pregnant or father a child while having this treatment. The drugs may harm the developing baby. It is important to use effective contraception during your treatment.

Breastfeeding

Women are advised not to breastfeed while having this treatment. This is because the drugs could be passed to the baby through breast milk.

Other medicines

Some medicines can affect the hormonal treatment or be harmful when you are having it. This includes medicines you can buy in a shop or chemist. Tell your cancer doctor about any drugs you are taking, including vitamins, herbal drugs and complementary therapies.

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.