Tamoxifen is an antiestrogen drug used in the treatment of breast cancer. It blocks the activity of estrogen, helping to stop the growth of some tumors. Overview: Tamoxifen is commonly used to treat certain types of breast cancer. It is also used to lower your risk of invasive breast cancer and keep some breast cancers from coming back. It blocks. Tamoxifen is a prescription medicine that is used to treat breast cancer in men and women. It is in a class known as a selective estrogen receptor modulator (SERM) and is used to treat hormone receptor-positive breast cancer. What Is Tamoxifen and How Does It Work? Tamoxifen is used to treat breast cancer that has spread to other parts of the body (metastatic breast cancer), to treat breast cancer in certain patients after surgery and radiation therapy, and to reduce the chances of breast cancer in high-risk patients. Tamoxifen (brand names: Nolvadex, Soltamox) is a medicine that blocks the effects of the hormone estrogen (called a selective estrogen receptor modulator, or SERM). Tamoxifen is a first choice among doctors for treating women who have not yet gone through menopause. Tamoxifen (Nolvadex), a hormone therapy drug, is used to treat hormone-receptor positive breast cancers. Tamoxifen and raloxifene have been shown to reduce the risk of breast cancer for some women. Learn more about these medications and their possible side effects. Tamoxifen is a nonsteroidal SERM of the triphenylethylene family and was structurally derived from diethylstilbestrol -like estrogens and antiestrogens such as chlorotrianisene and ethamoxytriphetol. [103][104][105][106] Initially, clomifene was synthesized, and tamoxifen was developed subsequently. [103][105][106] Tamoxifen is closely related. Tamoxifen is used to treat some types of breast cancer in men and women. Tamoxifen is also used to lower a woman's chance of developing breast cancer if she has a high risk (such as a family history of breast cancer). Tamoxifen is a hormone therapy drug. You might have it as a treatment for breast cancer. Find out about how you have it and possible side effects.