Ethynyl estradiol

Ethinyl estradiol, also sometimes written as 17α-ethinyl estradiol, ethinylestradiol, ethynyl estradiol, or ethinyl œstradiol, 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.

Transdermal ethinyl estradiol carries a greater risk of clot formation and venous thromboembolism than naturally occurring 17β-estradiol, which some have theorized to be related to different amounts of hepatic metabolism after absorption. The same contraindications and precautions apply for EE2 as with other estrogen medications.

Estinyl was a preparation of EE2 alone that was used for the management of menopausal symptoms and female hypogonadism.

EE2 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 (without progestogen) is of endometrial cancer. As such, the medication is generally prescribed with progesterone in the setting of birth control.