Letros (active agent – letrozole) is an oral non-steroidal aromatase inhibitor. In bodybuilding letrozol is used by males to reduce estradiol levels in blood by eliminating the production of estradiol through binding to and disabling the aromatase enzyme, which is responsible for the conversion (or aromatization) of androgens into estradiol.
In some cases, letrozole can be used as a treatment for gynecomastia, although it is probably most effective at this if caught in an early stage.
Letrozole also carries the ability to increase natural testosterone production through an increase of the luteinizing hormone (LH) and the follicle stimulating hormone (FSH), but this is normally not the preferred method of treatment.

