Ethinylestradiol

Ethinylestradiol is a synthetic estrogen used in various hormonal therapies. It is the 17α-ethynyl derivative of estradiol, formulated for effective oral activity. In clinical practice, ethinylestradiol is a core component of many combined oral contraceptives, typically paired with a progestin, and is also used in some estrogen-containing hormone replacement therapy regimens.

Mechanism and effects: Ethinylestradiol acts as an agonist of estrogen receptors, producing systemic estrogenic effects. In contraceptives, it suppresses the hypothalamic-pituitary-ovarian axis via negative feedback on gonadotropin release (LH and FSH), thereby inhibiting ovulation and stabilizing the endometrium. The ethynyl modification increases oral potency and duration of action compared with natural estradiol.

Pharmacokinetics: Ethinylestradiol is well absorbed when taken by mouth and is highly bound to plasma proteins. It is metabolized in the liver through hydroxylation and subsequent conjugation, with the ethynyl group contributing to its metabolic stability and prolonged activity relative to estradiol.

Safety and contraindications: Common side effects include nausea, breast tenderness, headaches, and mood changes. Its use carries an increased risk of venous thromboembolism, particularly with advancing age, smoking, obesity, or certain genetic factors. Contraindications include pregnancy, active thromboembolic disease, liver disease, estrogen-dependent tumors, and certain cardiovascular or thrombotic conditions.

See also: combined oral contraceptives; hormone replacement therapy; estrogen.