Synthetic, orally active substances with effects resembling those of progesterone have become available. They differ not only in dosage but also in the details of their action on various organs. Their double effect in preparing the uterus for nidation and suspending ovulation should make them useful in both the positive and the negative aspects of planned parenthood. The antifertility action has been tested by 715 patients using five different preparations. After exclusion of imperfect data there remained observations on 3,082 months of therapy with 22 pregnancies, giving a pregnancy rate of 8.6% as compared with about 4% for other contraceptive measures. Both unfavorable and favorable side-effects were reported. The use of progestational drugs in this way depends not on local but on systemic actions, the extent of which has not been completely determined. Nevertheless, it suggests a relatively simple form of family planning in addition to other important uses in gynecology and obstetrics.
Tyler ET, Olson HJ. FERTILITY PROMOTING AND INHIBITING EFFECTS OF NEW STEROID HORMONAL SUBSTANCES. JAMA. 1959;169(16):1843-1854. doi:10.1001/jama.1959.03000330015003