An orally bioavailable pentafluoroethyl derivative of a mifepristone-related steroid with antiprogestagenic activity. Lonaprisan is a pure, highly receptor-selective progesterone receptor (PR) antagonist; binding of this agent to PRs inhibits PR activation and the associated proliferative effects. Unlike many other antiprogestins such as mifepristone, this agent does not appear to convert to an agonist in the presence of protein kinase A (PKA) activators and shows high antiprogestagenic activity on both progesterone receptor (PR) isoforms PR-A and PR-B.