Comparative studies of the ethynyl estrogens used in oral contraceptives. I. Endometrial response.

Reproductive-age women were given identically prepared mestranol or ethynylestradiol orally for two consecutive 21 day cycles in doses ranging from 50 to 100 mug per day. Endometrial biopsies were obtained at the end of the second cycle and assessed for estrogenic effect. At these dose levels and with this treatment regimen, no differences could be detected between doses or between drugs, indicating that a plateau in endometrial response was reached.