Letrozole (also known as Femera) is an oral non-steroidal aromatase inhibitor (AI) that was developed to treat hormone receptor-positive breast cancer. It is by far the strongest and most potent of the three most popular aromatase inhibitors. When anabolic steroids are used, some of those steroids convert into estradiol via the aromatase enzyme (aromatization), resulting in all the respective estrogen side effects. Bodybuilders use letrozole to block the aromatase enzyme from converting androgens to estrogen, thereby reducing estradiol levels by inhibiting the production of estradiol. Only one standard 2.5 mg tablet dose of letrozole is effective enough to reduce circulating estrogen levels by up to 98%. In some cases, it can be used as a treatment for gynecomastia, although letrozole is probably most effective for this purpose only when symptoms are caught at an early stage. Letrozole also carries the ability to increase natural testosterone production by helping to facilitate an increase in luteinizing hormone (LH) and follicle stimulating hormone (FSH), but this is normally not the preferred method of treatment. 

WARNING: Do not exceed recommended dosages! As an aromatase inhibitor for bodybuilding purposes, even in the presence of exogenous anabolic steroids, a 2.5 mg dose will usually be too high and could potentially result in suffering the undesirable symptoms of estrogen deficiency and a significant loss of energy; in fact, it’s almost guaranteed. For standard estrogenic-related protection, a 0.5–1 mg dose every other day should be more than enough. 

Post-cycle therapy (PCT)