Nolvadex D tablets contain the active ingredient tamoxifen citrate, which is a type of medicine known as an 'anti-oestrogen'. (NB. Tamoxifen is also available without a brand name, ie as the generic medicine.) Tamoxifen is mainly used to treat women with breast cancers that respond to the female sex hormone, oestrogen. Most breast cancers are sensitive to oestrogen, and their growth is increased in the presence of this hormone. Oestrogen binds to oestrogen receptors on the breast cancer cells and causes changes within the cells that result in faster growth of the cancer. Breast cancers that are sensitive to oestrogen are called oestrogen receptor positive cancers. Tamoxifen works by blocking the oestrogen receptors, thereby blocking the effect of oestrogen 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. Tamoxifen is also used in the treatment of female infertility that is caused by problems with ovulation. Again, it acts by blocking oestrogen receptors, this time in a part of the brain called the hypothalamus. The effect of this is an increase in the levels of the hormones that control the development and release of an egg. These hormones are released from the pituitary gland and are known as follicle stimulating hormone (FSH) and luteinising hormone (LH). FSH stimulates the ovaries and LH causes the release of an egg from the ovaries (ovulation). In the normal menstrual cycle, oestrogen acts on receptors in the hypothalamus after ovulation. This causes the pituitary gland to stop releasing FSH and LH. As tamoxifen blocks the oestrogen receptors in the hypothalamus, it prevents this action of oestrogen. FSH and LH levels therefore increase, which increases the chances of egg development and ovulation.