Although many antiprogestins are under investigation by pharmaceutical companies for various therapeutic purposes, mifepristone is the only antiprogestin that has been extensively studied in human beings. It has been most widely studied as a means of nonsurgical abortion in early pregnancy, and has been licensed for that purpose in France, the United Kingdom, and Sweden. Because of the perceived promise of this class of compounds for a variety of therapeutic uses, the Institute of Medicine (IOM) established a committee of seven individuals to assess the state of scientific knowledge about antiprogestins, to clarify what is and is not known about these compounds, and to make recommendations for future research that might lead to improvements over currently available therapies for a variety of conditions.

Political controversy has focused public attention on the use of antiprogestins to induce miscarriage; this committee, however, was specifically charged with considering the full spectrum of clinical applications of antiprogestins, not just their use for medical abortion.

Using information provided in the literature, in commissioned papers, and presented during a workshop held at the IOM in April 1993, the committee reviewed and assessed the basic and clinical research available on the use of antiprogestins for post-coital contraception, continuous-use contraception, induction of missed menses, first-trimester termination of pregnancy, second-trimester termination of pregnancy, as well as induction of labor, and for the treatment of endometriosis, uterine leiomyomas, meningioma, breast cancer, and Cushing's syndrome. The committee made a series of general recommendations that included several cross-cutting issues for investigation, as well as specific recommendations for research on each of the topics discussed at the workshop. Those recommendations appear below. The committee's full report includes a more complete explanation of its conclusions and presents additional materials supporting its recommendations. The background papers prepared for the IOM workshop are included as Appendix B of this report.


Recommendation No. 1. Research is needed to define the basic mechanisms and modes of action of mifepristone (RU 486) and other antiprogestins in order to understand the effects that have already been demonstrated and to develop compounds with more specific antiprogestin activity.

Recommendation No. 2. Because antiprogestins as a class have clear potential for preventive and therapeutic applica-

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