Morning-After Contraception

Diethylstilbestrol usage as an effective postcoital contraceptive has been lauded

Abstract, 1974

During the past 5 years much emphasis has been placed on the development of an effective postcoital contraceptive (an intraceptive, or “morning-after” pill). Much of the impetus toward this goal has come from college health services and from rape cases. The idea is not new. In 1926, Smith and Parkes and Bellerby demonstrated that administration of estrogen could inhibit pregnancy in laboratory animals. The mechanism of this action was considered to be either a change (increase or decrease) in tubal transport or an effect on the endometrium. Within a few months after the synthesis of DES, Parkes et al. reported a similar DES effect in rabbits. Interestingly, in 1969 Dodds remarked that the possible human implications of this work had not occurred to them in 1939, and so development of oral contraceptives had been delayed many years.

It was the mid 1960’s before DES was again studied actively as a postcoital agent. Primarily through the work of Morris and van Wagenen in primates, DES was shown to be very effective. Kuchera reported the first large series in humans, noting no pregnancies among 1,000 exposures, wherein 20 to 40 pregnancies would have been expected. Morris commented in February 1972 that of “several thousand” midcycle exposures treated with DES, only three failures were known.

The results of these trials prompted the FDA to approve DES for use as a postcoital antifertility agent. The present dosage recommended is 25 mg twice daily for 5 days, beginning within 72 hours of exposure. Because failure can occur (though it is unlikely), the patient must be warned of the possibility of a late effect-Le., development of genital adenocarcinoma-in female offspring. And if pregnancy does ensue, therapeutic abortion should be considered.

The mechanism by which DES prevents pregnancy in humans is not clear. Large doses of most estrogens prevent pregnancy. Ethinyl estradiol has been studied extensively in this regard and is effective. But since a small amount of estrogen is known to be necessary for implantation in most species, including man, small doses of estrogens may promote rather than prevent gestation. Various antiestrogenic drugs also have been shown to prevent pregnancy in some species, but the “results are various and not confirmed in humans. A recent study has confirmed the suspected decrease of plasma progesterone in women receiving DES postovulation and has suggested that this may be the primary reason for inhibition ofimplantation. Endometrial biopsies do not show a persistent proliferative phase; rather, secretory endometrium appears early and persists unchanged throughout the luteal phase. Another postulated explanation of the inhibition of implantation is that the decrease of progesterone causes a change in the concentration of carbonic anhydrase in the endometrium.


  • Diethylstilbestrol Usage: Its Interesting Past, Important Present, and Questionable Future, Medical Clinics of North America, sciencedirect, July 1974.
  • Image credit caseygueren.

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