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Definition of Tamoxifen (Nolvadex)
Medically reviewed by Min Clinic Staff | Updated: January 2026
Tamoxifen (Nolvadex): An antiestrogen (a drug that blocks the effects of estrogen) which competes with estrogen for binding sites in target tissues such as breast.
Tamoxifen has been widely publicized. It was approved by the US Food and Drug Administration (FDA) to treat breast cancer and help prevent it in women at high risk for the disease and, then in 2000, to treat women who have had surgery and radiation for ductal carcinoma in situ (DCIS) to lower the risk of invasive breast cancer arising from the intraductal carcinoma.