Arimidex (generic name is anastrozole) is a newer drug developed for the treatment of advanced breast cancer in women. It is manufactured by Zenica Pharmaceuticals and was approved for use in the United States at the end of December 1995. Specifically, Arimidex is the first in a new class of third-generation selective oral aromatase inhibitors.. It acts by blocking the enzyme aromatase, subsequently blocking the production of estrogen. Since many forms of breast cancer cells are stimulated by estrogen, it is hoped that by reducing amounts of estrogen in the body the progression of such a disease can be halted. This is the basic premise behind Nolvadex, except this drug blocks the action and not production of estrogen. The effects of Arimidex can be quite dramatic to say the least. A daily dose of one tablet (1 mg) can produce estrogen suppression greater than 80 % in treated patients. With the powerful effect this drug has on hormone levels, it is only to be used (clinically) by post-menopausal women whose disease has progressed following treatment with Nolvadex (tamoxifen citrate). Side effects like hot flushes and hair thinning can be present, and would no doubt be much more severe in pre-menopausal patients.