Equilin is one of the active components of estrogens used in estrogen replacement therapy. This compound is used as a sulfate conjugate in drug Premarin. Equili is an inhibitor of 17beta-hydroxysteroid dehydrogenase type 1 (17beta-HSD1), a key enzyme responsible for elevated levels of 17beta-estradiol (E2) in breast tumor tissues. Thus equilin reduce the E2 levels in breast tissues and hence the reduce risk of estrogen-dependent breast cancer.