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Letrozole - Brand name: Femara

On this page

  1. About letrozole
  2. Key facts
  3. Who can and cannot take letrozole
  4. How and when to take letrozole
  5. Side effects of letrozole
  6. How to cope with side effects of letrozole
  7. Pregnancy and breastfeeding
  8. Cautions with other medicines
  9. Common questions

1. About letrozole

Letrozole is a medicine used for treating breast cancer. It can also help prevent breast cancer coming back.

It is mainly prescribed for women who have been through the menopause and have a type of cancer called "hormone-dependent" breast cancer.

Most people who take letrozole will have had surgery, radiotherapy or sometimes chemotherapy to treat their breast cancer first.

Letrozole comes as tablets. It is available on prescription only.

Letrozole can sometimes also be used:

  • to prevent breast cancer if you are high risk and have been through the menopause
  • to treat breast cancer in men and younger women
  • as a fertility treatment if you have polycystic ovary syndrome

2. Key facts

  • You usually take letrozole once a day – try to take it at the same time each day.
  • Most people are given letrozole for 5 years, but some will take it for up to 10 years.
  • Common side effects can be like menopause symptoms and include hot flushes, difficulty sleeping, tiredness and low mood.
  • Side effects usually improve after a few months as your body gets used to the medicine.
  • Your doctor will monitor your blood pressure, cholesterol levels and bone density during your treatment.

3. Who can and cannot take letrozole

Letrozole can be taken by adults only (aged 18 years and over).

Letrozole is not suitable for some people. Tell your doctor before starting on this medicine if you:

  • have had an allergic reaction to letrozole or any other medicines in the past
  • still have periods
  • are pregnant, trying to get pregnant or breastfeeding
  • have serious kidney or liver disease
  • have been told you have fragile or brittle bones (osteoporosis)

4. How and when to take letrozole

Letrozole comes as 2.5mg tablets. The usual dose is 1 tablet, taken once a day.

Try to take your letrozole at the same time each day. You can choose a time that suits your everyday routine. This will make it easier to remember to take your medicine.

Swallow the tablet whole with a drink of water. Do not crush or chew it. You can take letrozole with or without food.

What if I forget to take it?

If you forget a dose take it as soon as you remember, unless your next dose is due in 2 or 3 hours. In this case skip the missed dose and take your next one at the usual time.

Do not take a double dose to make up for a forgotten dose.

If you forget doses often, it may help to set an alarm to remind you. You could also ask your pharmacist for advice about other ways to help you remember to take your medicine.

What if I take too much?

If you take too many letrozole tablets by accident, you may get symptoms like feeling sick, blurred vision or a fast heartbeat.

Urgent advice: Contact 111 for advice now if:

  • you take too many tablets and feel unwell

5. Side effects of letrozole

Like all medicines, letrozole can cause side effects, although not everyone gets them.

Common side effects

These common side effects happen in more than 1 in 100 people.

Menopause symptoms usually improve during the first few months of taking letrozole.

Talk to your doctor or a pharmacist if these side effects bother you or do not go away:

  • hot flushes and sweating
  • dry or itchy vagina, bleeding from your vagina
  • difficulty sleeping
  • feeling very tired
  • feeling or being sick, loss of appetite
  • mild aches in your muscles and bones
  • numb or tingling hands
  • changes to your skin, including a mild rash
  • hair loss
  • low mood or depression

Letrozole may also affect your blood pressure, cholesterol and bone density. Your doctor will monitor this carefully and can recommend additional treatment if needed.

Serious side effects

Serious side effects are rare and happen in less than 1 in 100 people.

Immediate action required: Call 999 or go to A&E if you have:

  • sudden weakness or lose feeling in any part of your body, if your face drops on 1 side or you have difficulty speaking – these can be signs of a stroke
  • very sudden and severe chest pain – this can be a sign of a heart attack

Urgent advice: Contact 111 now for advice if you have:

  • swelling and tenderness or pain along a vein – these can be signs of a blood clot
  • muscle weakness, pain or swelling in the joints or tendons in your ankle, calf or legs, shoulder or arms
  • a high temperature or chills – these can be signs of an infection
  • frequent mouth ulcers or frequent sore throat – these can be signs of problems with your white blood cells
  • yellow skin or the whites of your eyes turn yellow –
    this can be a sign of liver problems
  • problems when you pee, including peeing more often or urgent need to pee – these can be signs of a urinary tract infection (UTI)
  • blurred vision

Serious allergic reaction

In rare cases, it's possible to have a serious allergic reaction (anaphylaxis) to letrozole.

Immediate action required: Call 999 or go to A&E if:

  • you get a skin rash that may include itchy, red, swollen, blistered or peeling skin
  • you're wheezing
  • you get tightness in the chest or throat
  • you have trouble breathing or talking
  • your mouth, face, lips, tongue or throat start swelling

You could be having a serious allergic reaction and may need immediate treatment in hospital.

These are not all the side effects of letrozole. For a full list, see the leaflet inside your medicines packet.


You can report any suspected side effect to the UK safety scheme.

6. How to cope with side effects of letrozole

Menopause symptoms such as hot flushes, difficulty sleeping, tiredness and low mood usually improve during the first months of taking letrozole. However, if they're severe or last longer than a few months, talk to your doctor or breast cancer nurse.


Find out more about treating symptoms of the menopause.

What to do about:

  • hot flushes and sweating – try cutting down on spicy food, caffeine, smoking and alcohol. It may help to keep the room cool and use a fan. Try spraying your face with cool water, or sipping a cold drink.
  • dry or itchy vagina, bleeding from your vagina – ask your doctor or breast cancer nurse to recommend a vaginal moisturiser for treating irritation or dryness. Vaginal bleeding usually happens in the first few weeks after starting letrozole. Talk to your doctor if it lasts longer than a few days. Also talk to your doctor if these symptoms first appear more than a few weeks after you start taking letrozole.
  • difficulty sleeping – avoid caffeine (tea, coffee, cola and chocolate) in the afternoon and evening. Keep your bedroom dark and quiet, and try going to bed and getting up at a set time each day. Stop watching TV and using electronic devices like mobiles or tablets at least 1 hour before bedtime.
  • feeling very tired – gentle exercise and eating healthily can help make you feel less tired. Try going to bed and getting up at a set time each day. Do not drive, ride a bike or operate machinery if you feel very tired while taking letrozole. Speak to your doctor if this problem does not gradually improve as your body gets used to the medicine.
  • feeling or being sick, loss of appetite – it might help to take letrozole after you've eaten. Choose foods you normally enjoy but avoid rich or spicy food. Try eating smaller meals but more often. If you're being sick, have small frequent sips of water to avoid dehydration. Talk to your doctor if your symptoms do not improve or get worse.
  • mild aches in your muscles or bones – ask a pharmacist to recommend a suitable painkiller. If the pain lasts more than a week ask your doctor for advice. If you have a sudden attack of pain in a joint ask a doctor for advice urgently.
  • numb or tingling hands – stop taking the medicine and ask your doctor for advice
  • changes to your skin, including a rash – it may help to take an antihistamine. You can buy these at a pharmacy without a prescription. Check with a pharmacist to see what is suitable for you.
  • hair loss – some people find their hair gets thinner when they start taking letrozole. This is usually mild. Ask your breast cancer nurse for advice if this is bothering you.
  • low mood or depression – it is difficult to know whether this is due to the medicine, dealing with menopausal symptoms or dealing with a diagnosis of cancer. Speak to your doctor or specialist nurse. They may recommend therapies, like cognitive therapy or mindfulness, or antidepressant medicines.

7. Pregnancy and breastfeeding

Letrozole is not recommended when pregnant or breastfeeding. This is because it can harm your baby.

Talk to your doctor urgently if there is any chance that you could be pregnant.

Non-urgent advice: Tell your doctor if you're:

  • pregnant
  • trying to get pregnant
  • breastfeeding

8. Cautions with other medicines

There are very few medicines that interfere with the way letrozole works in the body.

However, do not take any medicines like hormone replacement therapy that relieve menopausal symptoms. These may contain ingredients similar to the hormone oestrogen and could stop letrozole working as well as it should in treating your cancer.

Mixing letrozole with herbal remedies and supplements

Do not take any herbal remedies or supplements for menopausal symptoms while taking letrozole. These can stop letrozole working as well as it should.

There's very little information about taking other herbal remedies and supplements together with letrozole.


Tell your doctor and pharmacist if you're taking any other medicines, including herbal remedies, vitamins or supplements.

9. Common questions

How does letrozole work?

Letrozole belongs to a group of medicines called aromatase inhibitors.

Aromatase inhibitor medicines are used to treat certain types of breast cancer, where the cancer cells need oestrogen (a hormone) in order to grow.

After the menopause your ovaries stop producing oestrogen. Instead your body makes oestrogen from an enzyme called aromatase.

Aromatase inhibitors reduce the amount of aromatase in your body and this in turn stops your body producing oestrogen. This helps prevent cancer cells growing, as they no longer have anything to feed on.

What are the benefits of taking letrozole?

Letrozole helps stop your breast cancer coming back. By taking this medicine for 5 years (or sometimes up to 10 years), you have a better chance of being alive 15 years after your breast cancer was first diagnosed.

Your specialist will be able to explain the benefits and risks of taking letrozole.

They can also calculate how well letrozole is likely to work for you. This is done by comparing your details with those of more than 20,000 other people who have had treatment for breast cancer.

The exact benefits and how well it's likely to work for you depend on a combination of different things.

This varies for each person and includes factors like your age when the breast cancer was found, how it was found and whether you've had chemotherapy or not.

How long does it take to work?

Letrozole will immediately start to reduce the amount of oestrogen in your body.

However, it takes several weeks or months for the medicine to work fully.

During this time you're likely to have menopause symptoms as your body gets used to having less oestrogen. These symptoms will gradually improve as your body adjusts to the medicine.

How long will I take it for

Most people who take letrozole will have had surgery, radiotherapy or sometimes chemotherapy to treat their breast cancer first.

In this case, surgery, radiotherapy or chemotherapy is the first ("primary") treatment and letrozole is an additional ("adjuvant") therapy. Adjuvant therapy helps stop the cancer coming back.

Most people will have adjuvant therapy for 5 years. However, sometimes your doctor will advise continuing it for longer. During this time you may be given letrozole only, or tamoxifen (a drug that can also be used to treat breast cancer) for a few years followed by letrozole for the remaining time.

Letrozole is sometimes used to treat cancer if you cannot have surgery, or to shrink the cancer before surgery if you cannot have chemotherapy. In this case your specialist will tell you how long to take the medicine for.

Is it safe to take for a long time?

Letrozole is generally safe to take long term, however, your specialist team will monitor your health carefully.

This is because letrozole reduces levels of oestrogen that your body needs for strong and healthy bones. If you take letrozole for a long time your bones can become weaker (osteoporosis) and more likely to break.

You will have bone density scans before you start taking letrozole, 1 or 2 years into treatment and again after you finish your treatment.

Your doctor may recommend a type of medicine called a bisphosphonate to help reduce bone damage. They can also give you advice on exercise and diet to help keep your bones strong.

Letrozole can also increase your blood pressure and cholesterol levels. Your doctor will monitor these during your regular check-ups and recommend treatment as needed.

Can I stop taking it?


Do not stop taking letrozole without talking to your doctor first.

If you want to stop taking it for any reason, your doctor will be able to discuss alternatives for treating your breast cancer or preventing it coming back.

Sometimes people are given a short break from letrozole. This can help if you are getting side effects such as joint pain. However, only take a break from your medicine if you have discussed it with your specialist first and they agree to it.

Are there other medicines like letrozole?

Medicines such as tamoxifen, anastrazole and exemestane work in a similar way to letrozole. These medicines lower your oestrogen levels and can cause similar side effects.

However, medicines affect people in different ways. If you are bothered by side effects from taking letrozole, talk to your doctor. They may want to try you on one of these other medicines instead.

Can I drink alcohol with it?

There is no evidence that drinking alcohol causes any problems when taking letrozole.

Some people taking letrozole may get hot flushes or redness when they drink alcohol. In this case, avoiding alcohol may help.

Is there any food or drink I need to avoid?

Most people can eat and drink normally when taking letrozole. Although some people may get hot flushes or redness when they drink alcohol.

Some people find letrozole affects their appetite.

If you lose your appetite, try to make sure you have a balanced diet by eating smaller meals and more often.

If it makes you feel hungrier and you're putting on too much weight, ask your doctor or specialist nurse to refer you to a dietitian.

Will it affect my contraception or fertility?

Letrozole is generally only given to you if you have gone through the menopause.

However, some people find they start having periods again after taking letrozole. If this happens to you, it's important to use reliable contraception. Talk to your doctor if your periods start again, or if there is any chance that you are pregnant.

Letrozole is not recommended during pregnancy.

Can I drive or ride a bike?

Some people feel extremely tired when taking letrozole.

If you feel tired or dizzy, or if you get blurred vision, do not drive, cycle or operate machinery until you feel OK again.

Page last reviewed: 21 July 2020
Next review due: 21 July 2023