As much as everyone raves about Letrozole due to its effects on paper, I personally feel there are better drugs for users on steroid cycles that come with far less potential side effects. It is not the best cancer fighting drug for women in pre-menopausal, actually it’s completely ineffective as the main source of estrogen is from the ovaries. However it has been proven highly effective in post-menopausal women due to estrogens from the peripheral tissues. It is not normally used in a first line defence for cancer fighting as many doctors have found favour with Tamoxifen.

Exemestane (Aromasin) is an oral steroidal aromatase inhibitor, but unlike letrozole and anastrozole it permanently binds to the active site of the aromatase enzymes thus blocking their function of converting androgens into estrogens. This is known as Type I or suicide inhibition because the inhibitor becomes inactive due to the mechanism of its actions. A permanent bond with the aromatase enzyme complex is formed and prolonged effects may be experienced even after the drug has cleared from circulation. The aromatase enzyme’s activity can only be restored by new enzyme synthesis.