Tamoxifen | Cancer Research UK
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This page tells you about the hormone therapy tamoxifen and its possible side effects. There are sections about


What tamoxifen is

Tamoxifen is a hormone therapy for breast cancer. It is occasionally used to treat other types of cancer, but the information here refers to its use for breast cancer.

There is general information about hormone therapies in the cancer treatment section.


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 women who are ER positive. That means that their breast cancer cells have oestrogen receptors (ER). The oestrogen receptor is the part of the breast cancer cell that oestrogen locks on to, stimulating the cell to divide and grow. Tamoxifen blocks the oestrogen receptor. It lowers the risk of breast cancer coming back (recurring) after surgery or developing in the other breast. 

Breast cancer is rare in men but tamoxifen can be a helpful treatment if the cancer is ER positive. We have information about breast cancer in men, which includes information about the possible side effects of tamoxifen treatment.

To find out if your cancer has hormone receptors, your specialist will arrange tests on your breast cancer cells. Your specialist may also prescribe tamoxifen if your cancer cells are ER negative, but have progesterone receptors (are PR positive).


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.

It is very important that you take tablets 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. Most women take tamoxifen for 5 years. 

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

We've listed the side effects associated with tamoxifen below. You can use the links to find out more about each side effect. Or you can go to the cancer drug side effects section for general information.


Common side effects

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

  • Hot flushes and sweats – around 45% of women have moderate to severe hot flushes and sweats while taking tamoxifen
  • 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
  • Fatigue (tiredness) affects about 1 out of 4 women (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 – do not drive or operate machinery if you have this
  • Eye problems can very occasionally occur, such as eyesight changes, cataracts or changes in the back of the eye (retina) – it is important to have regular eye check ups while having tamoxifen. If you notice any changes in your eyesight tell your doctor

Occasional side effects

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

  • Fluid build up may cause ankle and or finger swelling (or weight gain) in about 1 in 10 people (10%)
  • Weight gain – some people put on weight while they are taking tamoxifen
  • Headaches
  • 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
  • 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
  • Hair thinning is usually only slight and not noticeable
  • Bone pain and pain in the area of the tumour – tell your doctor or nurse as painkillers can help
  • Leg cramps – walking may help to stretch the muscle and ease this

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 is finished, but you will have regular blood tests to check how well your liver is working
  • A skin rash
  • Womb cancer – there is a very slight increase risk of developing a cancer of the womb. If you have any abnormal bleeding, or other symptoms that concern you, tell your doctor or nurse so that you can have a check up

Important things to remember

The side effects above 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)
  • Other drugs you are having

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. Tamoxifen may react with 

  • Anastrozole (another type of breast cancer treatment)
  • The contraceptive pill – talk to your nurse about other forms of contraception you can use
  • Some anti depressant medicines
  • Some drugs to treat heart conditions
  • Some anti acid medicines for indigestion
  • Some other anti cancer drugs – your doctor and pharmacist will check this
  • Medicines used to treat disorders of the parathyroid glands
  • The anti clotting drug warfarin – if you are taking warfarin you will have regular blood tests, and your doctor may need to adjust your dose of warfarin


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.


Tamoxifen may have a harmful effect on a developing baby. Before you start treatment let your doctor or nurse know if there is any possibility that you may be pregnant.

It is important not to become pregnant while taking this treatment and for at least 2 months afterwards. Even if your periods have stopped while taking the treatment, you could become pregnant. Discuss contraception with your doctor or nurse before the treatment starts. 


Breastfeeding is not advisable during this treatment because the drug may come through in the breast milk.


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 www.mhra.gov.uk.

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Updated: 4 September 2013