What is tamoxifen?

Tamoxifen is a drug widely used to treat breast cancer. Tamoxifen (brand names include Nolvadex-D, Tamoxifen-Sandoz and Genox) blocks the effect of oestrogen, a female hormone, in the breast. The growth of some breast cancers is thought to be stimulated by oestrogen (this is called 'oestrogen-receptor positive' breast cancer).

Does tamoxifen work on all breast cancers?

Tests can show whether the breast cancer cells have special 'markers' on them - called hormone receptors. If these markers are present, the cancer is described as 'hormone receptor positive' and the cancer is more likely to respond to hormone treatment.

When is tamoxifen used?

Those women whose cancers have 'receptors' are usually advised to take tamoxifen after surgery and radiation treatment to reduce the risk of breast cancer returning.

Tamoxifen may also be used to treat breast cancer if it returns or has spread.

How long is tamoxifen taken for?

Tamoxifen is taken as a tablet, usually one tablet each day. To help prevent the return of breast cancer, tamoxifen is usually taken for 5 years. Taking it beyond 5 years has been shown to be of no benefit and may increase side effects.

If breast cancer has returned, tamoxifen is usually taken for as long as it helps.

Side effects of tamoxifen

Many women on tamoxifen experience no side effects.

Side effects can include:

• hot flushes
• periods becoming irregular or stopping
• bleeding or discharge from the vagina
• dry or itchy vagina
• nausea or indigestion
• dizziness
• skin rash
• headache
• depression
• tiredness, sleep problems 
• weight gain.

Some of these effects may disappear in 1-2 weeks. Women who have not yet been through the menopause may be more likely to experience hot flushes and irregular periods. If side effects are a problem, talk to your doctor.

If you are taking other medicines, especially warfarin or coumarin-type anti-coagulant drugs, tell your doctor, as they could interact with tamoxifen.

When to take tamoxifen

If you have nausea, try taking tamoxifen with food or just before bed. If you miss a tablet, take it as soon as you remember. Then continue to take your tablets as before. It is best to consult your doctor before stopping tamoxifen.

Benefits of taking tamoxifen

When used after surgery for breast cancer, tamoxifen delays or prevents the return of cancer in up to 20% of women. It also helps to reduce the chances of cancer occurring in the other breast.

When used after breast cancer returns, tamoxifen helps control the cancer in 20-50% of women.

Risks from taking tamoxifen

Taking tamoxifen increases your risk of endometrial cancer. Your doctor will help you weigh up the benefits of preventing breast cancer against the risk of developing endometrial cancer.

Symptoms to report

If you are taking tamoxifen and have any of these symptoms, you should see your doctor:

• abnormal vaginal bleeding, such as:
  - bleeding after menopause
  - bleeding between periods
  - heavier than normal periods
• changes in discharge from the vagina
• lower abdominal pain or pressure.

Eyes may be affected

Very occasionally, tamoxifen causes eye damage, for example, damage to your cornea or retina, and may increase the risk of developing cataracts.

Ask your doctor to refer you to an ophthalmologist (eye specialist) if you have any of these symptoms:

• blurred vision lasting more than 1 week
• change in colour vision.

DVT risk increases

Tamoxifen increases the risk of developing blood clots in the deep vein of the leg (DVT - deep vein thrombosis). Tell your doctor if you have leg pain or swelling, or if you feel breathless (as clots can travel to the lungs).

Avoid pregnancy while taking tamoxifen

Tamoxifen may cause harm to an unborn child if taken during pregnancy. If you could become pregnant, you should use a cap or condom with a spermicide, or an IUD, but not use hormone-based contraception. Discuss suitable contraception with your doctor. Contraception must also be continued for two months after the end of tamoxifen treatment.

If you become pregnant, you should stop taking tamoxifen and inform your doctor.

If you have any questions or concerns about tamoxifen, consult your doctor.

Related topics

Also see Breast cancer and Breast cancer treatment

What does that term mean? See Cancer glossary

Original material provided by the Cancer Society, 2003. Reviewed by everybody, July 2010.