Tamoxifen is used to treat breast cancer. It is sometimes used to treat other cancers and conditions. It may also be used to prevent breast cancer.

What is tamoxifen?

Tamoxifen is a hormonal therapy drug used: 

  • to reduce the risk of breast cancer coming back and to prevent a new cancer developing in the other breast – you take it for a number of years 
  • to treat secondary breast cancer

Tamoxifen is also sometimes used to: 

  • reduce a woman’s risk of breast cancer developing if they have a higher risk because of family history  
  • treat other types of cancer
  • treat or prevent breast tenderness and swelling (gynaecomastia) – this can be a side effect of some hormonal therapies used for prostate cancer.

Tamoxifen can be given alone, with other hormonal therapies, 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.

Side effects for men and people assigned male at birth

Most of what we know about tamoxifen side effects comes from research about breast cancer in women. There is less research about side effects when tamoxifen is used to treat men or people assigned male at birth. 

The information on this page is written for anyone having tamoxifen as part of their cancer treatment. But for men and people assigned male at birth some side effects below: 

  • may be less common. This may depend on why you are having tamoxifen and how long you take it for. Ask your doctor or nurse for more information. 
  • will not be relevant. Information about vaginal or womb side effects are written for women and people assigned female at birth. 

How tamoxifen 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 the hormone oestrogen to grow. This type of breast cancer is called oestrogen receptor-positive (ER-positive) breast cancer. Tamoxifen blocks oestrogen from reaching the cancer cells.

Taking tamoxifen tablets or syrup

Tamoxifen comes as tablets or syrup you can take at home. You may have tamoxifen on its own, or with other drugs. Your nurse or doctor will talk to you about your treatment plan. 

Always take the tablets or syrup exactly as explained. This is important to make sure they work as well as possible for you. For the treatment or prevention of cancer, you usually take tamoxifen daily. Try to take it at the same time every day. 

If you forget to take your tamoxifen, 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 or syrup:

  • Keep them in the original package and at room temperature, away from heat and direct sunlight.
  • Keep them safe and out of sight and reach of children.
  • If you are sick just after taking the tablets or syrup, contact your healthcare team. Do not take another dose.
  • Get a new prescription before you run out of tablets or syrup, and make sure you have plenty for holidays.
  • If your treatment is stopped, return any unused tablets or syrup 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. You may have some rarer side effects that we have not listed here.

If you are having other cancer treatments, 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.

You can read more about coping with hot flushes.

Vaginal dryness

This treatment can cause vaginal dryness and itching. 

If you have this side effect, non-hormonal creams, gels or lubricants may help. You can buy these from a chemist, or your doctor can prescribe them. We have more information about cancer and sex

Vaginal bleeding and effects on periods

This treatment can cause vaginal bleeding or change the usual pattern of periods.

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. 

If you have periods, you may find they become irregular, lighter, or sometimes stop altogether during this treatment. This does not always mean you are unable to get pregnant. Even if your periods stop or are irregular when taking this treatment, you still need to use contraception to prevent a pregnancy. Your doctor or nurse can tell you more about this.

Feeling sick

This treatment can make you feel sick. Any sickness usually improves after a few weeks. Try taking tamoxifen with food or at night.

Let your doctor or nurse know if you continue to feel sick. They can give you advice or drugs to help.

Feeling tired (fatigue)

Feeling tired is a common side effect. Try to pace yourself and plan your day so you have time to rest between activities.

Being physically active can help to manage tiredness and give you more energy. It also:

  • helps you sleep better
  • reduces stress
  • improves your bone health.

If you feel sleepy, do not drive or operate machinery.

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.

Skin changes

This treatment may affect your skin. It 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.

Rarely, this treatment may cause a more serious skin condition. You may have a skin rash which then blisters and your skin can peel. You may also feel unwell with flu-like symptoms such as a high temperature and joint pain. If you have any of these symptoms, you should stop taking tamoxifen and contact the hospital straight away.

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.

Fluid build-up (oedema)

You may find your ankles or fingers become swollen when taking this drug. This is caused by a build-up of fluid, which is called oedema. It is usually mild. If you notice any swelling or puffiness, ask your nurse or doctor for advice.

Leg cramps and muscle pain

Walking may stretch the muscles and help with this. Let your doctor or nurse know if leg cramps or muscle pains are a problem.


This treatment may cause headaches. If you have headaches, tell your doctor. They may give you painkillers to help.

Diarrhoea and constipation

This treatment can cause constipation or diarrhoea. If this is a problem, tell your doctor or nurse.

Eye problems

This treatment may cause cataracts (clouding of the lens of the eye) or other eye problems. If you get blurry vision or notice any change in your vision, always tell your doctor or nurse. If your vision is affected, it is important not to drive or operate machinery.

Effects on the nervous system

This treatment can affect the nervous system. You may have pins and needles, or feel tingling in your arms and legs. You may also feel dizzy or unsteady, or have taste changes. Tell your doctor or nurse if you notice any of these symptoms.

It is important not to drive or operate machinery if you feel dizzy.

Blood clot or stroke

Tamoxifen increases the risk of a blood clot or stroke. Your doctor will give you advice about reducing this risk. They may give you drugs to reduce your risk while you are taking tamoxifen. 
Symptoms of a blood clot include:

  • throbbing pain, redness or swelling in a leg or arm
  • suddenly feeling breathless or coughing
  • sharp chest pain, which may be worse when you cough or take a deep breath. 

Symptoms of a stroke include:

  • the face, mouth or eye may have drooped on one side
  • weakness or numbness in one arm
  • problems with speech, talking or understanding.

If you have any of these symptoms, contact the hospital straight away on the 24-hour contact number you have been given. If you cannot get through to your doctor, call the NHS urgent advice number on 111.

Effects on the womb

This treatment can cause changes to the lining of the womb that may cause vaginal bleeding. Rarely, tamoxifen can cause womb cancer.

The benefits of taking tamoxifen usually outweigh the risk of womb cancer. Always tell your doctor if you have irregular or unexpected bleeding or discharge from the vagina. They will arrange tests if needed to check for changes to the lining of the womb.

You should also tell them if you have any pain or pressure in the lower tummy (pelvis). This can be an early sign of womb cancer, although it is usually caused by other conditions. If womb cancer is found early, treatment can be very successful.

Effects on the liver

This treatment may affect how your liver works. This is usually mild. You will have blood tests to check how well your liver is working.

Other information


Your doctor will advise you not to get pregnant or make someone pregnant while having this treatment. The drugs may harm a developing baby. It is important to use contraception during your treatment and for a while after treatment finishes. Your doctor, nurse or pharmacist can tell you more about this.


Some cancer drugs can affect whether you can get pregnant or make someone pregnant. If you are worried about this, it is important to talk with your doctor before you start treatment.


You are advised not to breastfeed while having this treatment, or for some time after treatment finishes. This is because the drugs could be passed to the baby through breast milk.

Your doctor or nurse can give you more information.

Other medicines

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


Tamoxifen syrup contains alcohol. Tell your doctor, nurse, or pharmacist if this is a problem for you. This may affect your ability to drive or operate machinery.

Glycerol and sorbitol

Tamoxifen syrup contains sugars called glycerol and sorbitol. If you have been told by a doctor that you cannot digest some sugars, talk to your doctor before taking this drug.


These tablets contain a type of sugar called lactose. If you have been told by a doctor that you cannot digest some sugars or are lactose intolerant, talk to your doctor before taking this drug.

Medical and dental treatment

If you need medical treatment for any reason other than cancer, always tell the doctors and nurses 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.

About our information

  • Reviewers

    This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert health professionals and people living with cancer.

    Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information.

Date reviewed

Reviewed: 01 March 2022
Next review: 01 September 2024
Trusted Information Creator - Patient Information Forum
Trusted Information Creator - Patient Information Forum

Our cancer information meets the PIF TICK quality mark.

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