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.
Type II aromatase inhibitors (letrozole and anastrozole) inhibit the enzyme by binding reversibly to the aromatase enzyme through competitive inhibition which does not destroy the enzyme and inhibition are stopped upon clearance of the drug.
For bodybuilders this is of significant value because it means that estrogenic rebound is not possible upon the removal of exemestane. Other aromatase inhibitors will disassociate from the enzyme, eventually allowing renewed androgen to estrogen synthesis.
Exemestane is often combined with tamoxifen during PCT. Doing so allows for an enhanced anti-estrogenic effect when both the enzyme (exemestane) and receptor (tamoxifen) sites are blocked. The added advantage of using exemestane over other aromatase inhibitors is that the aromatase enzyme stays deactivated long after the PCT protocol finishes. This prevents estrogenic activity from resuming immediately and thus causing estrogenic side-effects again. Instead the aromatase enzymes will slowly return to normal function. The addition of tamoxifen also has a positive effect on cholesterol.
Side effects associated with the use of aromatase inhibitors include nausea, vomiting, hot flashes, joint pain, weakness, fatigue, mood changes, depression, high blood pressure and headache. Bone mineral density may also decrease, which may lead to osteoporosis. Extended periods of low estrogen levels may lead to cardiovascular disease and immune system changes, so limit usage to a maximum of two months.
Normally 10 to 25mg is used daily and estrogen suppression may be up to 85% according to the packaging leaflet.
Aromasin is not easily obtainable on the black-market and when found is usually very expensive and a single month’s supply might exceed R1600. Fortunately underground labs produce generics that are up to four times cheaper.