Equilin sulfate is one of the main component, which is responsible for the pharmacological action of the PREMARIN, conjugated estrogens tablets. Premarin is used to treat the moderate to severe vasomotor symptoms, vulvar and vaginal atrophy due to menopause. It is also used to treat hypoestrogenism due to hypogonadism, castration or primary ovarian failure; to treat breast cancer and advanced androgen-dependent carcinoma of the prostate (for Palliation Only). In addition, premarin is used to prevent postmenopausal osteoporosis. Equilin sulfate is a prodrug, which is hydrolyzed to the corresponding free estrogen equilin, an inhibitor of 17beta-hydroxysteroid dehydrogenase type 1 (17beta-HSD1). Human 17beta-HSD1 catalyzes the reduction of inactive estrone (E1) to the active 17beta-estradiol in breast tissues, is a key enzyme responsible for elevated levels of E2 in breast tumor tissues. Thus equilin reduce the E2 levels in breast tissues and hence the reduce risk of estrogen-dependent breast cancer.