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.
Tamoxifen is sometimes used in women who have a high risk of breast cancer, to prevent breast cancer from developing.
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 liquid.
You should take the right dose, not more or less.
Talk to your healthcare team before you stop taking a cancer drug, or if you miss a dose.
When you have tamoxifen
You take it daily at the same time every day.
To treat breast cancer, most people take tamoxifen for 5 years. In some situations you might take tamoxifen for 10 years.
To prevent breast cancer, you take tamoxifen for 5 years.
You might have some blood tests during treatment to check your hormone levels.
How often and how severe the side effects are can vary from person to person. They also depend on what other treatments you're having.
When to contact your team
Your doctor, nurse or pharmacist will go through the possible side effects. They will monitor you during treatment and check how you are at your appointments. Contact your advice line as soon as possible if:
- you have severe side effects
- your side effects aren’t getting any better
- your side effects are getting worse
Early treatment can help manage side effects better.
We haven't listed all the side effects here. Remember it is very unlikely that you will have all of these side effects, but you might have some of them at the same time.
Common side effects
These side effects happen in more than 10 in 100 people (10%). You might have one or more of them. They include:
Fluid build up
You may have swelling of your hands and legs due to a build up of fluid (oedema).
Changes to periods
Your periods may become irregular or stop while taking tamoxifen. It might still be possible for you to become pregnant. So you should still take contraception to prevent pregnancy. Talk to your doctor about any changes.
Feeling or being sick
Feeling or being sick is usually well controlled with anti sickness medicines. Avoiding fatty or fried foods, eating small meals and snacks, drinking plenty of water, and relaxation techniques can all help.
It is important to take anti sickness medicines as prescribed even if you don’t feel sick. It is easier to prevent sickness rather than treating it once it has started.
Tiredness and weakness (fatigue)
Tiredness and weakness (fatigue) can happen during and after treatment. Doing gentle exercises each day can keep your energy up. Don't push yourself, rest when you start to feel tired and ask others for help.
This might include bleeding or discharge from the vagina. Talk to your doctor about this.
We have some tips for coping with hot flushes and the possible treatments for men and women. Talk to your doctor if your hot flushes are hard to cope with. They might be able to prescribe you some medicines.
If you're finding it difficult to manage your hot flushes, try taking half your dose in the morning and half in the evening. Always talk to your doctor before changing the dose of any prescription medicine.
Skin problems include a skin rash, dry skin and itching. This usually goes back to normal when your treatment finishes. Your nurse will tell you what products you can use on your skin to help.
Occasional side effects
These side effects happen in between 1 and 10 out of every 100 people (1 to 10%). You might have one or more of them. They include:
- leg cramps
- hair thinning or hair loss
- feeling light headed
- eye problems, such as blurred vision, due to damage of the retina
- an allergic reaction
- breathlessness and looking pale (anaemia)
- itchiness in the vulval area – talk to your doctor as this could be an infection and might need treatment
- changes to the lining of the womb and non cancerous growths – tell your doctor if you have unexpected or irregular vaginal bleeding
- a blood clot in the deep veins of your body (deep vein thrombosis, DVT) that could possibly travel to your lungs (pulmonary embolism). This could be life threatening if not treated quickly
Symptoms of a blood clot includes:
- pain, redness and swelling around the area where the clot is and may feel warm to touch
- pain in your chest or upper back – dial 999 if you have chest pain
- coughing up blood
Rare side effects
These side effects happen in fewer than 1 in 100 people (1%). You might have one or more of them. They include:
- cancer of the womb – tell your doctor if you have regular or unexpected vaginal bleeding
- liver problems such as liver failure
- inflammation of the lungs causing breathlessness and a dry cough
Coping with side effects
We have more information about side effects and tips on how to cope with them.
What else do I need to know?
Other medicines, foods and drink
Cancer drugs can interact with some other medicines and herbal products. Tell your doctor or pharmacist about any medicines you are taking. This includes vitamins, herbal supplements and over the counter remedies.
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 with this drug and for at least 2 months afterwards.
Talk to your doctor or nurse about effective contraception before starting treatment. Let them know straight away if you or your partner falls pregnant while having treatment.
It is not known whether this drug comes through into the breast milk. Doctors usually advise that you don’t breastfeed during this treatment.
The liquid form of tamoxifen contains a very small amount of alcohol. This is not harmful to most people but may be a problem if you have alcoholism.
Treatment for other conditions
Always tell other doctors, nurses, pharmacists or dentists that you’re having this treatment if you need treatment for anything else, including teeth problems.
More information about this treatment
For further information about this treatment go to the electronic Medicines Compendium (eMC) website.
You can report any side effect you have to the Medicines Health and Regulatory Authority (MHRA) as part of their Yellow Card Scheme.
This page is due for review. We will update this as soon as possible.