Anastrozole lowers estrogen levels, which may slow the growth of certain types of breast tumors that need estrogen to grow. Arimidex is used to treat breast cancer in postmenopausal women, often when the cancer has progressed even after taking tamoxifen (Nolvadex, Soltamox). Arimidex been studied for use by infertile men to balance testosterone levels and maintain a healthy sperm count. Male athletes and bodybuilders who take anabolic steroids to build muscle also take Arimidex to reduce the estrogen production that is a side effect of steroid use.