Tamoxifen is a drug that has been prescribed for over 20 years to treat breast cancer that is estrogen sensitive. Sometimes called an "anti-estrogen", tamoxifen functions by interfering with estrogen binding in breast tissue, thus stopping estrogen sensitive breast cancer cells from growing. Paradoxically, however, it acts as an estrogen in other parts of the body, so some doctors tout its beneficial effects in combatting osteoporosis and heart disease.
Tamoxifen hasn't been proven to stop estrogen sensitive breast cancer from developing, but it has been shown to reduce the development of this type of cancer in the opposite breast of a woman who has already had breast cancer. It is usually prescribed for post-menopausal women as an adjuvant therapy in early stages of the disease or for those whose cancer has metastasized; its benefit is highest for postmenopausal women with estrogen sensitive breast cancer, but may help those with non-estrogen sensitive breast cancer as well. However, it loses its effectiveness within five years. Premenopausal women with either type of breast cancer receive less benefit, and are usually given chemotherapy instead. Tamoxifen has been shown to reduce the risk of estrogen-sensitive breast cancer in women who do not yet have the disease, but are presumed to be at high risk of developing the disease.
Tamoxifen has side effects, some of them quite serious. Because of its mechanism, it may induce menopause in perimenopausal women, and even if it does not, often causes hot flashes, depression, irregular menstruation, and other premenopausal symptoms. Tamoxifen has other potentially fatal side effects, including increased risk of blood clots, thrombosis, and uterine cancer, and may harm the liver, possibly causing hepatitis. In some women it causes permanent eye damage, including cataracts.
Tamoxifen is a controversial drug which elicits strong pro and anti views. For positive views, see
http://www.cancerbacup.org.uk/info/tamoxifen.htm
http://www.graylab.ac.uk/cancernet/600716.html
Very negative views of tamoxifen, often citing the same studies, are at
http://www.innerself.com/Health/tamoxifen.htm
http://www.all-natural.com/tamox.html
The best thing you can do, if you think you might need tamoxifen or any other drug, is to become well-informed. I am considered at fairly high risk of breast cancer as my mother and one of her sisters died of this disease before they reached the age of 50. I have done a lot of research on cancer in general and breast cancer in particular, and have chosen lifestyle change as a primary prevention measure. For me, cancer prevention is all about healthy living, but different people are comfortable with different regimes. Tamoxifen may be the right choice for you.