ORG33628

ORG33628 is a potent and selective small molecule progesterone receptor (PR) antagonist (antiprogestin) with high selectivity over the glucocorticoid receptor (GR). Originally developed by Organon, the compound was investigated in Phase II clinical trials for female contraception, specifically to improve cycle control and manage vaginal bleeding in progestin-only contraceptive regimens. However, development was discontinued because the combination compromised ovulation inhibition. ORG33628 has also been evaluated in preclinical models for its potential in breast cancer prevention and treatment, as well as other hormone-dependent conditions like uterine leiomyomas and endometriosis.