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What tamoxifen is

Tamoxifen is a hormone therapy for breast cancer in both women and men. It lowers the risk of early breast cancer coming back (recurring) after surgery or developing in the other breast. It can also control advanced breast cancer for some time.

The liquid version of tamoxifen is called Saltamox.

Tamoxifen is sometimes used to treat other types of cancer in clinical trials.


How tamoxifen works

Many breast cancers are stimulated to grow by the female sex hormones oestrogen and progesterone. These breast cancers are called hormone sensitive or hormone receptor positive. Tamoxifen is usually prescribed for people who have oestrogen receptors in the breast cancer cells. These cells are called oestrogen receptor positive or ER positive. 

Tamoxifen works by locking on to the oestrogen receptors to block oestrogen from attaching to them. The oestrogen cannot then stimulate the cells to divide and grow. 


How you have tamoxifen

Tamoxifen comes as a tablet that you swallow. It is also available as a sugar free liquid called Saltamox. You take it daily at the same time every day. It is important to keep the tablets or liquid out of the reach of children. Most people take tamoxifen for 5 years. 

It is very important that you take medicines according to the instructions your doctor or pharmacist gave you. Whether you have a full or empty stomach, for example, can affect how much of a drug gets into your bloodstream. You should take the right dose, not more or less. And never stop taking a cancer drug without talking to your specialist first. 

If you accidentally take more tamoxifen than you should, let your doctor or nurse know straight away. If you forget to take a dose, take the dose as soon as you remember, unless it is nearly time for your next dose. Don't take a double dose to make up for a forgotten dose.


Tests during treatment

You have blood tests before starting treatment and regularly during your treatment. The tests check your levels of blood cells and other substances in the blood. They also check how well your liver and kidneys are working.

You may also have eye tests and tests to check your womb lining. 


About side effects

We've listed the side effects associated with tamoxifen. You can use the links to find out more about each side effect. Where there is no link, please go to our information about cancer drug side effects or use the search box at the top of the page.

You may have a few side effects. They may be mild or more severe. A side effect may get better or worse through your course of treatment. Or more side effects may develop as the course goes on. This depends on

  • How many times you've had the drug before
  • Your general health
  • The amount of the drug you have (the dose)

The side effects may be different if you are having tamoxifen with other medicines.

Tell your doctor or nurse straight away if any of the side effects get severe.


Common side effects

More than 10 in every 100 people have one or more of these.

  • Hot flushes and sweats – around 40 out of 100 people (40%) have moderate to severe hot flushes and sweats while taking tamoxifen and for some time afterwards
  • Tiredness and weakness (fatigue) affects about 1 out of 4 people (25%)
  • Discharge from the vagina, dryness and itching affect about 1 in 10 women. Tell your doctor or nurse if you have any of these side effects
  • Feeling light headed – don't drive or operate machinery if you have this
  • Eye problems can occur, such as eyesight changes, cataracts or changes in the back of the eye (retina). If you notice any changes in your eyesight tell your doctor
  • Feeling or being sick usually happens at the start of treatment and goes after a few days or weeks – it tends to be mild and easily controlled by anti sickness tablets
  • Hair thinning is usually slight and not noticeable
  • Fluid build up may cause ankle and or finger swelling (or weight gain) in about 1 in 10 people (10%)
  • Leg cramps – walking may help to stretch the muscle and ease this
  • Changes to your periods – if you haven’t had your menopause your periods may become irregular. Some women find that their periods stop. They usually start again within 6 to12 months of treatment finishing. However, for some women who are close to the time of their natural menopause they don’t start again

Occasional side effects

Between 1 and 10 in every 100 people have one or more of these.

  • Weight gain – some people put on weight while they are taking tamoxifen
  • Headaches
  • Being sick – let your doctor or nurse know if you have this
  • Sadness or depression – about 1 in 10 people (10%) have some change in their mood. Let your doctor or nurse know if you feel sad or depressed
  • Bone pain and pain in the area of the tumour if you have advanced cancer – tell your doctor or nurse as painkillers can help

Rare side effects

Fewer than 1 in 100 people have these.

  • Tumour flare – if you have cancer that has spread to your bones, you may have some increased pain when you first start taking tamoxifen. This is called tumour flare. Very rarely it makes you feel sick, thirsty or constipated. These symptoms can be signs that the level of calcium in your blood has gone up. If you have any of these symptoms, tell your doctor or nurse
  • Your risk of blood clots (thrombosis) can slightly increase when you take tamoxifen. If you or a close relative have had a blood clot in the past tell your doctor. Let them know if you have pain, redness or swelling in your legs or if you have sudden breathlessness, chest pain or cough up blood
  • Liver changes that are very mild and unlikely to cause symptoms – the liver will almost certainly go back to normal when treatment ends
  • A skin rash
  • Womb cancer – there is a very slight increased risk of developing a cancer of the womb. If you have any abnormal bleeding, or other symptoms that worry you, tell your doctor or nurse so that you can have a check up

Important things to remember

Coping with side effects

Talk to your doctor, pharmacist or nurse about all your side effects so they can help you manage them. They can give you advice or reassure you. Your nurse will give you a contact number to ring if you have any questions or problems. If in doubt, call them.

Other medicines

Tell your doctor about any other medicines you are taking, including vitamins, herbal supplements and over the counter remedies. Some drugs can react together.

Pregnancy and contraception

This drug may harm a baby developing in the womb. It is important not to become pregnant or father a child while you are having treatment and for at least 2 months afterwards. Even if your periods have stopped while taking the treatment, you could become pregnant. Talk to your doctor or nurse about effective contraception before starting treatment.


Don't breastfeed during this treatment because the drug may come through in the breast milk.


The liquid form of tamoxifen (Saltamox) contains a very small amount of alcohol. This is not harmful to most people but may be a problem if you have alcoholism.


More information about tamoxifen

This page does not list all the very rare side effects of this treatment that are very unlikely to affect you. For further information look at the Electronic Medicines Compendium website at www.medicines.org.uk.

If you have a side effect not mentioned here that you think may be due to this treatment you can report it to the Medicines Health and Regulatory Authority (MHRA) at yellowcard.mhra.gov.uk.

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Updated: 28 September 2015