Tamoxifen (ta-MOX-i-fen) is a drug that is used to treat many types of cancers. Some cancers are hormone sensitive (estrogen or progesterone receptor positive) and their growth can be affected by blocking the effect of the hormone estrogen. Tamoxifen is a hormone therapy used to treat hormone receptor-positive breast cancer. It can greatly reduce the risk of cancer recurrence (return) and invasive cancer. 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 citrate is a type of hormone therapy called a selective estrogen receptor modulator (or SERM). It works by binding to estrogen receptors, blocking estrogen’s effects in some tissues while mimicking its effects in others. 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. 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 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.