Dienogest -13C,15N,d4 (STS 557-13C,15N,d4) is the 13 C, 15 N and deuterium labeled isotope of Dienogest. Dienogest (STS-557) is an orally active and selective progesterone receptor agonist that effectively reduces the gene expression of COX-2 , mPGES-1 and aromatase. Dienogest also inhibits the mRNA and protein expression of PGE 2 synthase and the activation of NF-κB. Dienogest can be used in studies of endometriosis, menopause and menorrhagia.