Arimidex contains a substance called anastrozole. This belongs to a group of medicines called ‘aromatase inhibitors’. Arimidex is used to treat breast cancer in women who have gone through the menopause.Arimidex works by cutting down the amount of the hormone called estrogen that your body makes. It does this by blocking a naturalsubstance (an enzyme) in your body called ‘aromatase’. The active substance is anastrozole. Each film-coated tablet contains 1 mg of anastrozole.−The other ingredients are: lactose monohydrate povidone sodium starch glycollate magnesium stearate hypromellose macrogol 300 titanium dioxide.