Tamoxifen is an anti-oestrogen drug. It works by preventing oestrogen in the body from attaching to breast cancer cells and encouraging them to grow. Tamoxifen is the standard hormonal therapy for premenopausal women with breast cancer but it can also be given to some postmenopausal women.
Tamoxifen is taken daily as a tablet. The side effects are similar to the effects of the menopause and may include:
Tamoxifen can slightly increase the risk of womb (endometrial) cancer in postmenopausal women. Always tell your doctor if you have any abnormal vaginal bleeding. Tamoxifen may also slightly increase the risk of blood clots in the leg and lungs. Tell your doctor straight away if you have pain, warmth, swelling or tenderness in an arm or leg, or any chest pain.
Although this sounds frightening, these side effects are uncommon and the benefits of taking tamoxifen outweigh the risks for most women. If they do happen, they can usually be treated successfully.
Tamoxifen is sometimes used instead of an aromatase inhibitor (AI) in women who have problems with their bones, as it doesn’t cause bone thinning in postmenopausal women.
We have more detailed information on tamoxifen, including how it works, how it’s taken and the side effects it may cause.