Tamoxifen, sold under the brand name Nolvadex among others, is a selective estrogen receptor modulator used to prevent breast cancer in women and treat breast cancer in women and men. It is also being studied for other types of cancer. It has been used for Albright syndrome. Tamoxifen is typically taken daily by mouth for five years for breast cancer. Serious side effects include a small increased risk of uterine cancer, stroke, vision problems, and pulmonary embolism. Common side effects include irregular periods, weight loss, and hot flashes. It may cause harm to the baby if taken during pregnancy or breastfeeding. It is a selective estrogen-receptor modulator (SERM) and works by decreasing the growth of breast cancer cells. It is a member of the triphenylethylene group of compounds. Tamoxifen was initially made in 1962, by chemist Dora Richardson. It is on the World Health Organization's List of Essential Medicines. Tamoxifen is available as a generic medication. In 2020, it was the 317th most commonly prescribed medication in the United States, with more than 900thousand prescriptions. Medical uses Dysmenorrhea Tamoxifen has been used effectively to improve blood flow, reduce uterine contractility and pain in dysmenorrhea patients. Breast cancer Tamoxifen is used for the treatment of both early and advanced estrogen receptor-positive (ER-positive or ER+) breast cancer in pre- and postmenopausal women. Tamoxifen increases the risk of postmenopausal bleeding, endometrial polyps, hyperplasia, and endometrial cancer; using tamoxifen with an intrauterine system releasing levonorgestrel might increase vaginal bleeding after 1 to 2 years, but reduces somewhat endometrial polyps and hyperplasia, but not necessarily endometrial cancer. Additionally, it is the most common hormone treatment for male breast cancer. It is also approved by the FDA for the prevention of breast cancer in women at high risk of developing the disease. It has been further approved for the reduction of contralateral (in the opposite breast) cancer. The use of tamoxifen is recommended for 10 years. In 2006, the large STAR clinical study concluded that raloxifene is also effective in reducing the incidence of breast cancer. Updated results after an average of 6.75 years of follow up found that raloxifene retains 76% of tamoxifen's effectiveness in preventing invasive breast cancer, with 45% fewer uterine cancers and 25% fewer blood clots in women taking raloxifene than in women taking tamoxifen. Infertility Tamoxifen is used for ovulation induction to treat infertility in women with anovulatory disorders. It is