Epostane (INN, USAN, BAN) (developmental code name WIN-32729) is an inhibitor of 3ò-hydroxysteroid dehydrogenase (3ò-HSD) that was developed as a contraceptive, abortifacient, and oxytocic drug but was never marketed. By inhibiting 3ò-HSD, epostane blocks the biosynthesis of progesterone from pregnenolone (and also the conversion of dehydroepiandrosterone to androstenedione), thereby functioning as an antiprogestogen and terminating pregnancy. The drug was trialed and in a study was found to be slightly more effective at inducing abortion relative to mifepristone.