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Most breast cancers are sensitive to estrogen (oestrogen), and their growth is increased in the presence of this hormone. Tamoxifen works by blocking the estrogen receptors, thereby blocking the effect of estrogen on the cancer. This starves the breast cancer cells and stops them from growing. Tamoxifen helps prevent breast cancer from spreading to other areas of the body and also reduces risk of developing cancer in the other breast.
By blocking estrogen receptors Tamoxifen is also used in the treatment of female infertility that is caused by problems with ovulation. The effect is an increased levels of the hormones that control the development and release of an egg from the ovaries (ovulation). In the normal menstrual cycle, estrogen acts on receptors in the hypothalamus after ovulation. This causes the pituitary gland to stop releasing FSH and LH. As tamoxifen blocks the estrogen receptors in the hypothalamus, it prevents this action of estrogen. FSH and LH levels therefore increase, which increases the chances of egg development and ovulation.
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