Arimidex is an aromatase inhibitor. Many anabolic steroids convert to estrogen after they are administered. The process of conversion is due to the aromatase enzyme; Arimidex actively inhibits the enzyme therefor the estrogen conversion doesn’t take place and therefore does not bind leading to unwanted side-effects. Arimidex is useful when one is prone to gynecomastia and using moderate amounts of such steroids. Arimidex can achieve a high degree of estrogen blockade.