[4] The medication was under development for clinical use, for instance in the treatment of breast cancer and as an endometrial contraceptive, but was discontinued during phase III clinical trials in 1995 due to findings that liver function abnormalities developed in a majority patients.

[8][5][9] As of 2016, onapristone has re-emerged and is under development for the treatment of prostate cancer, currently in phase II clinical trials.

[10] Reaction of the steroid derivative (1) and the Grignard reagent 4-(dimethylamino)phenylmagnesium bromide (2) gives (3) by vinylogous addition to the epoxide.

Oxidation of the alcohol group in the five-membered ring to a ketone gives compound (4).

Irradiation of this material for 16 minutes with a mercury lamp results in the methyl group adjacent to the ketone changing from the beta to the alpha configuration, giving (5).