Pharmacological profile of estrogens in oral contraception.

The synthetic estrogen ethinylestradiol (EE)given by mouth is stable and yields satisfactory results in terms of ovulation inhibition and effects on the endometrium. It increases however the risk especially for venous thrombotic events and to a lesser degree also arterial thrombosis. Therefore research focused on diminuition of the EE dosage and the development of a different estrogen component in oral contraceptives, specifically an estrogen occurring during physiological processes in the female body. Two estrogens emerge: 17ß Estradiol is the most potent natural estrogen and it is the major estrogen secreted by the ovaries. Estetrol is a human sex steroid (15 alpha hydroxyestriol) which is only produced during pregnancy by the fetal liver. The pharmacolokinetic and pharmacodynamic properties of these estrogens are compared to those of EE (absorption, metabolization, bioavailability etc.) and the clinical profile is described as far it is known from a limited number of studies.