ARIMIDEX (anastrozole) tablets for oral administration contain 1 mg of anastrozole, a non-steroidal aromatase inhibitor. It is chemically described as 1,3-Benzenediacetonitrile, a, a, a', a'tetramethyl-5-(1H-1,2,4-triazol-1-ylmethyl). Its molecular formula is C17H19N5 and its structural formula is: