Ethynyl Estradiol (17α-Ethynylestradiol;Ethynylestradiol) is an orally bio-active estrogen used in almost all modern formulations of combined oral contraceptive pills.Target: Estrogen ReceptorEthynyl Estradiol (17α-Ethynylestradiol;Ethynylestradiol), also sometimes written as ethinylestradiol, ethynyl estradiol, or ethinyl estradiol, is a derivative of 17β-estradiol (E2), the major endogenous estrogen in humans. Ethynyl Estradiol (17α-Ethynylestradiol;Ethynylestradiol) is an orally bioactive estrogen used in many formulations of combined oral contraceptive pills. It is one of the most commonly used medications for this purpose. Transdermal ethinyl estradiol carries a greater risk of clot formation and venous thromboembolism than 17 beta estradiol, which some have theorized to be related to different amounts of hepatic metabolism after absorption. The same contraindications and precautions apply for EE as with other estrogen medications.Ethynyl Estradiol was a preparation of Ethynyl Estradiol alone that was used for the management of menopausal symptoms and female hypogonadism. Ethynyl Estradiol (17α-Ethynylestradiol;Ethynylestradiol) is released into the environment as a xenoestrogen from the urine and feces of people who take it as a medication. The major concern with unopposed estrogen is of endometrial cancer. As such, the medication is generally prescribed with progesterone in the setting of birth control. The first orally active semisynthetic steroidal estrogen, Ethynyl Estradiol, the 17α-ethynyl analog of E2, was synthesized in 1938 by Hans Herloff Inhoffen and Walter Hohlweg at Schering AG in Berlin.

References:
[1]. Djerassi C. Chemical birth of the pill. 1992. Am J Obstet Gynecol. 2006 Jan;194(1):290-8.