Active Substance: Letrozole
Letrozole is a type II (non-steroidal) third generation aromatase inhibitor. Clinically it is used to treat postmenopausal women with either estrogen receptor positive or estrogen receptor unknown breast cancer.
In women, tumors that contain estrogen receptors are classified as estrogen receptor-positive (ER+) tumors. For Letrozole to be prescribed, a given tumor must have been diagnosed as estrogen receptor positive or estrogen receptor unknown.
In the world of bodybuilding it is used to reduce or eliminate excess estrogen caused by the use of aromatizing steroids.