Tamoxifen

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 must take tablets according to the instructions your doctor or pharmacist gives you.

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.

Tests

You might have some blood tests during treatment to check your hormone levels.

Side effects

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.

Contact your advice line immediately if you have signs of infection, including a temperature above 37.5C or below 36C.

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.

Vaginal changes

This might include bleeding or discharge from the vagina. Talk to your doctor about this.

Hot flushes

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 rash

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)
headaches
depression
pain
diarrhoea
constipation
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
breathlessness
pain in your chest or upper back – dial 999 if you have chest pain
coughing up blood

Tell your doctor immediately or go to A&E if you have any symptoms of a blood clot.

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.

Breastfeeding

It is not known whether this drug comes through into the breast milk. Doctors usually advise that you don’t breastfeed during this treatment.

Alcohol

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.