Synthetic and Natural Estrogens Estrone (E1), estradiol (E2) and estriol (E3) are the three estrogens. Synthetic estrogen (premarin) is made up of E1 and E2 estrogen. E1 is the main estrogen that the body makes post menopausally, and most researchers believe that high E1 levels increase the risk of breast cancer. Therefore, we no longer […]