Anastrozole, often called by its brand name Arimidex, is an aromatase inhibitor. When a male is undergoing testosterone replacement (TRT), the level of estradiol ( the predominant form of estrogen in men) can rise. The majority of estrogen in a man is the result of the aromatase enzyme complex converting testosterone to estradiol (E2) and Androstenedione to estrone. 

 

Anastrozole can be used on its own to enhance GnRH release from the pituitary gland to promote FSH release to enhance fertility and endogenous testosterone production. This can be more beneficial than the increase in estrogen levels often witnessed with clomid use.