Aromatase Inhibitors
These drugs prevent the aromatase activity that occurs by binding to the enzyme. Letrozole and Arimidex bind reversibly, whereas Aromasin binds irreversibly. This difference is significant, as Aromasin is less likely to cause a rebound after it is stopped, because the aromatase enzyme needs to build back up before estrogen conversion can occur. However, Letro and A-dex can become unbound, and begin conversion again.
The pharmokinetics of these differ greatly from men to women, as well. They typically reduce estrogen 35-50% in men, whereas they reduce it 75-98% in women, from a clinical perspective.
The use of an AI is clear… less estrogen means less estrogen that can bind to the ER, causing gyno.