antiprogestin
noun
an·ti·pro·ges·tin
| \ -prō-ˈjest-ən
\
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Medical Definition of antiprogestin
: a substance (such as mifepristone) that inhibits the action of progesterone in the body
RU-486 is an antiprogestin that is thought to compete with progesterone at the receptor site.— Charles Morgan, Nature, 15 Jan. 1987