Arimidex is used with other treatments, such as surgery or radiation, to treat early breast cancer in women who have experienced menopause (change of life; end of monthly menstrual periods). This medication is also used as a first treatment of breast cancer that has spread within the breast or to other areas of the body, in post-menopausal women.

This medication is also used to treat breast cancer in women whose breast cancer has worsened after taking tamoxifen (Nolvadex). Arimidex is in a class of medications called nonsteroidal aromatase inhibitors. Many breast cancer tumors grow in response to estrogen. Arimidex works by decreasing the amount of estrogen the body makes. This can slow or stop the growth of many types of breast cancer cells that need estrogen to grow.