In combination birth control pills, the contraceptive effect of the estrogenic component is primarily related to

The two estrogenic compounds used in oral contraceptives are ethinyl estradiol and its 3-methyl ether, mestranol. To become biologically effective, mestranol must be demethylated to ethinyl estradiol, because mestranol does not bind to the estrogenic cytosol receptor. The degree of conversion of mestranol to ethinyl estradiol varies among individuals; however, it is estimated that ethinyl estradiol is about 1.7 times as potent as the same weight of mestranol. The estrogenic component of birth control pills was originally added to control irregular endometrial desquamation resulting in undesirable vaginal bleeding.