Arimidex is an extremely powerful anti-estrogen officially belonging to the Aromatase Inhibitor (AI) family. This is perhaps the most commonly used AI and one of the most common anti-estrogens on the market. Arimidex has proven to be very effective in breast cancer treatment, and is a favorite anti-estrogen among many anabolic steroid users. Countless anabolic steroid users rely on Arimidex for on cycle estrogenic protection.