Formestane

Also known as 4-hydroxyandrostenedione (4-Hydroxyandrost-4-ene-3,17-dione).  An irreversible, “suicide” inhibitor of the aromatase enzyme (responsible for the conversion of androgens to estrogens).  Originally developed as a treatment for breast cancer, formestane is now sold as a bodybuilding supplement, and used primarily for estrogen control/post-cycle therapy.