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.

Hormone therapy

Hormones can stimulate some breast cancer cells to grow. Hormone therapy works by either lowering the amount of hormones in the body or by blocking them getting to breast cancer cells.

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.

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.

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. For example, your side effects could be worse if you're also having other drugs or radiotherapy.

Common side effects

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.

Feeling or being sick

Feeling or being sick is usually well controlled with anti sickness medicines.

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.

Vaginal changes

This might include bleeding or discharge from the vagina.

Hot flushes

Skin rash

Skin problems include a skin rash, dry skin and itching.

Occasional side effects

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
changes to the lining of the womb and non cancerous growths
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

Rare side effects

cancer of the womb
liver problems such as liver failure
inflammation of the lungs causing breathlessness and a dry cough