Estradiol 17-β, which is the natural estrogen in women, offers an alternative to ethinyl-estradiol to be used in combined oral contraceptives. Thanks to its biochemical structure, estradiol has a far lesser impact on the synthesis of hepatic proteins than ethinyl-estradiol, which is likely to result in a better metabolic and vascular profile. However and until lately, the different clinical trials that had investigated estradiol-containing oral contraceptives were limited by bleeding disturbances, with breakthrough and irregular bleeding and higher rates of discontinuation. Development of anti-gonadotropic progestins with a potent endometrial activity is likely to make possible their combination with estradiol in oral contraceptives. The objective of this current review is to provide an overview of the development of combined oral contraceptives containing natural estrogen from the respective biochemical and pharmacological characteristics of ethinyl-estradiol and estradiol.
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