Ethinylestradiol

Ethinylestradiol (EE) is an estrogen medication which is used widely in birth control pills in combination with progestins. Ethinylestradiol was widely used for various indications such as the treatment of menopausal symptoms, gynecological disorders, and certain hormone-sensitive cancers. It is usually taken by mouth but is also used as a patch and vaginal ring.

The general side effects of ethinylestradiol include breast tenderness and enlargement, headache, fluid retention, and nausea among others. In males, ethinylestradiol can additionally cause breast development, feminization in general, hypogonadism, and sexual dysfunction. Rare but serious side effects include blood clots, liver damage, and cancer of the uterus.

Ethinylestradiol is an estrogen, or an agonist of the estrogen receptors, the biological target of estrogens like estradiol. It is a synthetic derivative of estradiol, a natural estrogen, and differs from it in various ways. Compared to estradiol, ethinylestradiol is more resistant to metabolism, has greatly improved bioavailability when taken by mouth, and shows relatively increased effects in certain parts of the body like the liver and uterus. These differences make ethinylestradiol more favorable for use in birth control pills than estradiol, though also result in an increased risk of blood clots and certain other rare adverse effects.

Ethinylestradiol was developed in the 1930s and was introduced for medical use in 1943. The medication started being used in birth control pills in the 1960s. Ethinylestradiol is found in almost all combined forms of birth control pills and is nearly the exclusive estrogen used for this purpose, making it one of the most widely used estrogens. In 2022, the combination with norethisterone was the 80th most commonly prescribed medication in the United States with more than 8 million prescriptions. Fixed-dose combination medications containing ethinylestradiol with other hormones are available.