Tamoxifen
Tamoxifen is a cancer drug. It is used to treat breast cancer.
What is tamoxifen?
Tamoxifen is a hormonal therapy drug. It is used to treat breast cancer. It can be used to reduce the risk of breast cancer developing if there is a higher risk because of family history.
Tamoxifen may sometimes be used to treat other conditions.
It is best to read this information with our general information about hormonal therapies and the type of cancer you have.
Your cancer team 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 other 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 other people assigned male at birth some of the side effects we describe:
- may be less common – this may depend on why you are having tamoxifen and how long you take it for. Ask your nurse or doctor for more information.
- will not be relevant – information about vaginal or womb side effects are written for women and other people assigned female at birth.
More information about this treatment
This information is correct at time of publishing. But sometimes the types of cancer this treatment is used for, or treatment side effects, may change between revision dates.
You can talk to your cancer team if you want more detailed information about this treatment. Or visit the electronic Medicines Compendium (eMC) website, which has patient information leaflets (PIL) for individual drugs.
How tamoxifen works
Hormones help control how cells grow and what they do in the body. The hormone oestrogen can encourage some breast cancer to develop and grow. Tamoxifen is an anti-oestrogen drug. It stops oestrogen attaching to breast cancer cells and making them grow. It only works for breast cancer that is oestrogen receptor positive (ER positive).
How tamoxifen is given
You have tamoxifen as tablets or syrup you can take at home. You may have tamoxifen with other cancer drugs.
During your treatment, you will meet someone from your cancer team, such as a:
- cancer doctor
- specialist nurse
- specialist pharmacist.
This is who we mean when we mention doctor, nurse or pharmacist in this information.
Taking tamoxifen tablets or syrup
Your cancer team will discuss your treatment plan with you.
Always take the tablets or syrup exactly as they tell you to. This is important to make sure they work as well as possible for you. Try to take tamoxifen tablets or syrup at the same time every day.
If you forget to take the tablets or syrup, take the missed dose as soon as possible within the same day. If a full day has passed, do not take a double dose.
Other things to remember about your tablets or syrup:
- Keep them in the original package and at room temperature, away from moisture, heat and direct sunlight.
- Keep them safe, where children cannot see or reach them.
- If you are sick (vomit) just after taking them, do not take an extra dose. Take your next dose at the usual time.
- Get a new prescription before you run out, and make sure you have plenty for holidays.
- Do not throw away unused tablets or syrup. Return them to a pharmacy.
Your cancer team may also give you other medicines to take home. Take all your medicines exactly as they tell you to. 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 that are less common.
You may get some of the side effects we mention, but you are unlikely to get all of them. And you may have some side effects, including rarer ones, that we have not listed here.
Other cancer treatments may cause different side effects. If you are also having other cancer treatment, you may have other side effects.
When you have this treatment, you will have regular appointments with a doctor, nurse or pharmacist. Always tell them about any side effects you have. They can give you:
- drugs to help control most side effects
- advice about managing side effects.
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 a different type of hormonal therapy.
Serious and life-threatening side effects
Some cancer treatments can cause serious side effects. Sometimes, these may be life-threatening. Your doctor, nurse or pharmacist can explain the risk of these side effects to you.
Contact the hospital
Your doctor, nurse or pharmacist will give you 24-hour contact numbers for the hospital. If you feel unwell or need advice, you can call at any time of the day or night. Save these numbers in your phone or keep them somewhere safe.
Very 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. If you have white skin, your skin may look red. If you have black or brown skin, your skin colour may deepen. Flushes can last up to 5 minutes. You might also have sweats or feel anxious or irritable during a flush.
Here are some things you can do to reduce the effects of hot flushes:
- Wear natural fabrics, such as cotton.
- Wear layers so you can remove clothes as needed.
- Use cotton sheets and layers of bedding you can remove.
- Try cooling pads or pillows to keep you cool.
- Keep rooms cool or use a fan.
- Have cold drinks and avoid caffeine and alcohol.
You might have fewer hot flushes as your body adjusts to this treatment. You could try therapies to help you cope with hot flushes, such as:
- talking therapies like cognitive behaviour therapy (CBT)
- controlled breathing exercises
- yoga
- acupuncture.
If they do not improve, talk to your doctor. Certain drugs can help to improve hot flushes.
Flushes usually stop a few months after treatment ends. But some people continue to have them.
Vaginal discharge or bleeding
This treatment can cause vaginal discharge or bleeding.
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. 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.
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.
Feeling sick
Your doctor, nurse or pharmacist will prescribe anti-sickness drugs to help prevent or control sickness. Take the drugs exactly as they tell you to, even if you do not feel sick. It is easier to prevent sickness than to treat it after it has started.
If you feel sick, take small sips of fluid often and eat small amounts regularly. It is important to drink enough fluids. If you continue to feel sick, or if you are sick (vomit) 1 to 2 times in 24 hours, contact the hospital on the 24-hour number as soon as possible. They will give you advice. They may change your anti-sickness treatment. Let them know if you still feel sick.
Skin changes
This treatment may affect your skin. It may cause a rash, which may be itchy. Your doctor or nurse can tell you what to expect. If your skin feels dry, try using soap-free cleansers and unperfumed moisturising cream every day.
Always tell your doctor or nurse about any skin changes. They can give you advice and may prescribe creams or medicines to help. Changes to your skin usually improve when treatment ends.
Rarely, this treatment can cause a serious skin reaction that needs to be treated immediately in hospital.
Do not take any more of this treatment and contact the hospital straight away on the 24-hour number if you have any of these symptoms:
- a skin rash that is spreading
- blistering or peeling skin
- flu-like symptoms, such as a high temperature and joint pain
- sores on your lips or in your mouth.
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 feel low or depressed, or have mood swings, during this treatment. Talking to family and friends about how you feel might help. If mood changes last for more than a few weeks, tell your doctor, nurse or pharmacist. They can talk to you about different ways to manage low mood or depression.
Other side effects
Allergic reaction
This treatment might cause an allergic reaction. But this is not common. Signs of a reaction can include:
- a skin rash or itching
- feeling breathless or wheezy
- swelling of your face, mouth or throat.
If you feel unwell or have any of these signs, contact the hospital straight away on the 24-hour number. Do not take any more of this treatment until you have checked with them.
Always call 999 if swelling happens suddenly or you are struggling to breathe.
Hair thinning
While you are having this treatment, your hair may become thinner, drier and more brittle. This is usually mild. If you are worried about this, ask your nurse for advice on hair care.
Headaches
This treatment may cause headaches. If you have headaches, tell your doctor, nurse or pharmacist. They can give you advice about painkillers that may help. Tell them if the headache does not get better, or gets worse.
Constipation
This treatment can cause constipation. Constipation means that you are not able to pass stools (poo) as often as you normally do. It can become difficult or painful. 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 on the 24-hour number for advice. They can give you drugs called laxatives to help.
If you have not been able to pass stools for over 2 days and are being sick, contact the 24-hour number straight away.
Diarrhoea
This treatment may cause diarrhoea. Diarrhoea means passing more stools (poo) than is normal for you, or having watery or loose stools. You may also have stomach cramps. If you have a stoma, it may be more active than usual.
If you are passing loose stools 3 or more times a day and this is not normal for you, contact the hospital as soon as possible on the 24-hour number. Follow the advice they give you about:
- taking anti-diarrhoea medicines
- drinking enough fluids to keep you hydrated and to replace lost salts and minerals
- any changes to your diet that might help.
They might also ask you for a specimen of your stool to check for infection.
Leg cramps, bone or muscle pain
You may get leg cramps, bone pain or muscle pain with this treatment. Walking may help with this because it stretches the muscles. Let your doctor or nurse know if leg cramps, bone pain or muscle pain are a problem.
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.
Eye problems
This treatment may cause cataracts (clouding of the lens of the eye) or other eye problems. Rarely you may get pain, swelling in and around your eyes or lose your vision. 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.
Anaemia (low number of red blood cells)
This treatment can reduce the number of red blood cells in your blood. Red blood cells carry oxygen around the body. If the number of red blood cells is low, this is called anaemia. You may feel:
- very low in energy
- breathless
- dizzy and light-headed.
If you have these symptoms, contact the hospital straight away on the 24-hour number. You may need treatment for anaemia. If you are very anaemic, you may need a drip to give you extra red blood cells. This is called a blood transfusion.
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.
Raised level of fats in the blood
Blood clot risk
Cancer and some cancer treatments can increase the risk of a blood clot. Contact the hospital straight away on the 24-hour number if you have any of these symptoms during or after treatment:
- throbbing pain or swelling in a leg or arm
- reddening of the skin in the area – if you have black or brown skin, this can be harder to notice, but the skin might become darker
- suddenly feeling breathless or coughing.
Always call 999 if you have:
- chest pain
- difficulty breathing.
A blood clot is serious, but it can be treated with drugs called anticoagulants. These thin the blood. Your doctor, nurse or pharmacist can give you more information about preventing and treating blood clots.
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.
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.
Other important 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:
- medicines you have been prescribed
- medicines you buy in a shop, pharmacy or online
- vitamins or supplements
- herbal drugs and complementary or homeopathic therapies
- recreational drugs – for example, cannabis.
Alcohol
Some preparations of this treatment contain alcohol. If having alcohol is a problem for you, tell your doctor, nurse or pharmacist. Your blood alcohol level may be above the legal limit after you have the treatment. Do not drive or operate machinery for a few hours after having this treatment, even if you feel okay.
Lactose
This treatment may contain lactose. If you have a lactose allergy or intolerance, ask your doctor, nurse or pharmacist for more information.
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.
Contraception
Your doctor, nurse or pharmacist will advise you not to get or make someone pregnant while having this treatment. The drug may harm a developing baby. It is important to use contraception to prevent pregnancy. Follow their advice about:
- what types of contraception to use – for example, using barrier contraception instead of hormonal contraception like the oral pill
- how long after treatment you should continue to use contraception.
Fertility
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.
Breastfeeding
You are advised not to breastfeed while having this treatment, or for some time after treatment ends. This is because the drugs could be passed to the baby through breast milk.
Your doctor, nurse or pharmacist can give you more information.
Medical and dental treatment
If you need medical treatment for any reason other than cancer, always tell the healthcare professional that you are having cancer treatment. Give them the contact details for your cancer doctor or cancer team so they can ask for advice.
If you have appointments with a dentist, always tell them you are having cancer treatment. Talk to your cancer team before you have any dental treatment.
About our information
This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer.
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References
Visit the electronic Medicines Compendium (eMC) to download a Patient Information Leaflet (PIL) for more detailed information. The leaflet lists all known side effects.
Date reviewed
Our cancer information meets the PIF TICK quality mark.
This means it is easy to use, up-to-date and based on the latest evidence. Learn more about how we produce our information.
The language we use
We want everyone affected by cancer to feel our information is written for them.
We want our information to be as clear as possible. To do this, we try to:
- use plain English
- explain medical words
- use short sentences
- use illustrations to explain text
- structure the information clearly
- make sure important points are clear.
We use gender-inclusive language and talk to our readers as ‘you’ so that everyone feels included. Where clinically necessary we use the terms ‘men’ and ‘women’ or ‘male’ and ‘female’. For example, we do so when talking about parts of the body or mentioning statistics or research about who is affected.
You can read more about how we produce our information here.