Arimidex (Anastrozole) Anastrozole is an extremely powerful anti-estrogen officially belonging to the Aromatase Inhibitor (AI) family. Developed in the early 1990’s by Zenaca Pharmaceuticals and released in 1995 under the trade name Arimidex, 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, even more so than traditional Nolvadex (Tamoxifen Citrate), and is a favorite anti-estrogen among many anabolic steroid users. Countless anabolic steroid users rely on Arimidex for on cycle estrogenic protection. Many anabolic steroids have the ability to aromatase and lead to excess estrogen, which in turn can lead to some of the most commonly associated side effects of anabolic steroid use.