Progestogen potency in oral contraceptive pills

The most important target organs for combined oral contraceptive preparations are the anterior pituitary gland and the uterus. The long-term unopposed administration of estrogen produces endometrial hyperplasia and amenorrhea, which are unacceptable to most women and their medical advisors. Cyclic administration of progestogens in combination with the estrogen, however, produces predictable endometrial shedding and achieves a regular and acceptable bleeding pattern in most women. This was the main reason that the "delay of menses" test was adopted as the earliest clinical means of comparing the relative potencies of progestogens that were administered orally. Recently attempts have been made to compare the potency of progestogens on the other organ systems by the extrapolation of data derived from studies on the endometrium. This is inappropriate, inasmuch as the effects of progestogens and estrogens independently and in combination differ greatly depending on the target organ. In this article, the literature on this controversial subject is reviewed.