This factsheet explains briefly what tamoxifen is, how it works, when it may be prescribed, what the benefits are and what side effects may occur.
Tamoxifen is a drug commonly used as part of the treatment for breast cancer.
Tamoxifen is thought to work in several ways although at present we do not completely understand all its actions. 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 partly by blocking the effects of oestrogen on cancer cells, so stopping them from growing. This is why it is called an anti-oestrogen.