Ethinyl Estradiol is a derivative of 17β-estradiol (E2), the major endogenous estrogen in humans. EE2 is an orally bioactive estrogen used in many formulations of combined oral contraceptive pills and is one of the most commonly used medications for this purpose.More at:https://www.bocsci.com/ethinyl-estradiol-cas-57-63-6-item-72055.html