Estradiol (medication)
Estradiol is also available in the U.S. in combination with progestogens for the treatment of menopausal symptoms and as a combined hormonal contraceptive:Estradiol and estradiol esters are also available in custom preparations from compounding pharmacies in the U.S. This includes subcutaneous pellet implants, which are not available in the United States as FDA-approved pharmaceutical drugs. In addition, topical creams that contain estradiol are generally regulated as cosmetics rather than as drugs in the U.S. and hence are also sold over-the-counter and may be purchased without a prescription on the Internet.
Estriol (medication)
Estriol is an estrogen, or an agonist of the estrogen receptors, ERα and ERβ. It has been found to possess 11–14% and 18–21% of the relative binding affinities of estradiol for the human ERα and ERβ, respectively, while its relative transactivational capacities at these receptors were 11% and 17%, respectively. In addition to being a ligand of the classical nuclear ERs, estriol is an antagonist of the GPER, a membrane estrogen receptor, at high concentrations. This is in contrast to estradiol, which is an agonist of this receptor. Like other estrogens, estriol does not importantly interact with other steroid hormone receptors.