Tamoxifen

This section explains briefly what Tamoxifen is, how it works, when it may be
prescribed, what the benefits are and what side effects may occur.

Page Contents

What is Tamoxifen?
How does it work?
How do I know if Tamoxifen will work for me?
How much Tamoxifen do I take and when do I take it?
Does it matter if I miss a dose?
How long will I have to take Tamoxifen?
What are the benefits of Tamoxifen?
What are the side effects of Tamoxifen?
Can I take other drugs while I am taking Tamoxifen?
I am still having regular periods (pre-menopausal). Will Tamoxifen work for me?
Fertility and pregnancy
Can Tamoxifen stop breast cancer?
What happens after I stop taking Tamoxifen?
Further support
Help from Action Breast Cancer

What is Tamoxifen?

Tamoxifen is a drug commonly used as part of the treatment for some breast cancers. It belongs to a group of drugs known as hormone therapies and is also described as an anti-oestrogen drug.
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How does it work?

Hormones are substances that occur naturally in the body and control the growth and activity of normal cells. The female hormones oestrogen and progesterone can affect the growth of breast cancer cells. Some breast cancers are stimulated by the hormone oestrogen, which encourages cells to grow. These cancers are known as oestrogen receptor positive tumours. Tamoxifen works by blocking the effects of oestrogen on cancer cells, so stopping them from growing. This is why it is called an anti-oestrogen.
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How do I know if Tamoxifen will work for me?

Your cancer specialist doctor will order a test on your tumour, either after a biopsy or after surgery, to find out if Tamoxifen will be of benefit to
you. This test is called an oestrogen receptor test. If you are oestrogen receptor positive, this means your tumour has oestrogen receptors and you could benefit from Tamoxifen.
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How much Tamoxifen do I take and when do I take it?

Tamoxifen is available as a tablet and a liquid. The recommended dose is 20mg once a day. It doesn’t matter what time of the day it is taken and it can be taken with or without food.
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Does it matter if I miss a dose?

As Tamoxifen can take several weeks to reach a steady level in the blood, this level does not dramatically change over a short period. Missing a single dose will not do any harm, but in the long term, it is better to take it regularly.
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How long will I have to take Tamoxifen?

You will usually take Tamoxifen for five years although some people may be on it for longer. Trials are still in progress looking at what is the most beneficial length of time to take Tamoxifen.
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What are the benefits of taking Tamoxifen?

Taking Tamoxifen significantly reduces the risk of the cancer coming back and improves overall survival in all age groups. The benefits are greater where the tumour is oestrogen receptor positive. In women who have been through the menopause, Tamoxifen treatment slightly reduces bone loss. However, in younger women, Tamoxifen may not have this benefit. Therefore, younger women will need to discuss risks of osteoporosis (bone thinning) and possible scanning for this with their doctor. Eating a calcium-rich diet and getting some weightbearing exercise such as walking may also be important. There is also some evidence that Tamoxifen reduces cholesterol and may therefore reduce the risk of heart disease.
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What are the side effects of Tamoxifen?

Like any drug, Tamoxifen can have side effects. However, everyone reacts differently to drugs. Some people have more side effects than others, and some people have no side effects at all. Some side effects are mentioned below, but if you experience any new symptoms, it is important to discuss them with your GP, specialist or breast care nurse. In general, the benefits of taking Tamoxifen far outweigh the risks in women who are oestrogen receptor positive.

The most common side effects are similar to menopausal symptoms, such as hot flushes, night sweats, vaginal dryness or discharge, irregular periods, lighter periods or stoppage of periods. These symptoms are more common in women taking Tamoxifen before the menopause than after. For women experiencing menopausal symptoms, please see the section on Understanding and Managing Menopausal Symptoms.

Other possible side effects include headaches, vaginal irritation or discharge and leg cramps at night. A small number of women notice an increase in downy facial hair or changes to their singing voice.

Some women may have indigestion or mild nausea, although these symptoms usually improve with time. Many women find that they put on weight during their treatment, although there is no clear evidence linking this weight gain to Tamoxifen.

Tamoxifen can also affect the lining of the womb (endometrium), which may become thickened. In a very few cases it may cause polyps or ovarian cysts or, very rarely, cancer of the womb. If you have any unexpected your GP or specialist. Some studies have shown a slightly higher increase in blood clotting in women taking Tamoxifen. This may be a higher risk in women having chemotherapy drug treatment at the same time.

There is a very slight increased risk in changes in vision in women taking Tamoxifen. The risk is greater in women who have problems such as cataracts before they start to take Tamoxifen. A very rare side effect of Tamoxifen is hair loss.
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Can I take other drugs while I am taking Tamoxifen?

It is not advisable to take anticoagulants (drugs that thin the blood) such as Warfarin while you are on Tamoxifen. Always check with your specialist if you are concerned about taking any other medicines.
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I am still having regular periods (pre-menopausal) will Tamoxifen work for me?

Tamoxifen is effective for both pre- and post-menopausal women, particularly those whose breast cancer cells are oestrogen receptor positive.
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Fertility and pregnancy

If you are pre-menopausal, your periods may become irregular or stop. They may return once you stop taking Tamoxifen. Even if your periods stop while taking Tamoxifen, you could still become pregnant. You should not become pregnant while taking Tamoxifen as the risks to the foetus are unknown. It is important therefore, to use reliable non-hormonal contraception such as condoms, femidoms, a diaphragm or coil (IUD). If you wish to become pregnant after Tamoxifen treatment, you should discuss this with your doctor. It may be advisable to wait a couple of months after stopping the drug.
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Can Tamoxifen prevent breast cancer?

Trials are currently in progress which involve giving women who are at a high risk of developing breast cancer either Tamoxifen or a placebo (dummy pill) for five years. Preliminary results of a major study in the USA have shown a 45% reduction in breast cancer risk over a short-term period (compared with the group taking a placebo). However, studies looking at the long-term benefits and risks of the drug are ongoing and it will be several years before these longterm results are available.
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What happens after I stop taking Tamoxifen?

Many women feel insecure when they are told by their doctor that they should stop taking Tamoxifen after 5 years or so. This is natural and it may help to discuss your concerns with your GP, specialist doctor or breast care nurse specialist. In general, the side effects of Tamoxifen may outweigh the benefits after the recommended time of taking the drug.
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Further support

If you have any concerns about taking Tamoxifen you can talk to your specialist, chemotherapy nurse or breast care nurse. You might find it easier to share your feelings with someone who has had a similar experience to you. Reach to Recovery is a programme set up to help and support women who have recently had a breast cancer diagnosis. The programme works on the principle of personal contact between the patient and a Reach to Recovery volunteer – a woman who has had treatment for breast cancer. Carefully selected and fully trained volunteers are available to provide advice and reassurance at a time when a woman is most in need of both. For more information on individual support or support groups in your area, call the National Cancer Helpline on 1800 200 700.
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ABC would like to thank Breast Cancer Care in the UK for their permission to adapt the text in this factsheet from their series of factsheets.