Arimidex is the brand name of the generic drug Anastrazole, used to treat breast cancer in postmenopausal women. Arimidex belongs to class of drugs known as nonsteroidal aromatase inhibitors, which slow or stop the growth of breast cancers that are stimulated by estrogen by decreasing the amount of estrogen the body makes after menopause. Arimidex may also be used for purposes not listed in this medication guide.