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.
Estrone (medication)
Estrone is an estrogen, specifically an agonist of the estrogen receptors ERα and ERβ. It is a far less potent estrogen than is estradiol, and as such is a relatively weak estrogen. Given by subcutaneous injection in mice, estradiol is about 10-fold more potent than estrone and about 100-fold more potent than estriol. According to one study, the relative binding affinities of estrone for the human ERα and ERβ were 4.0% and 3.5% of those estradiol, respectively, and the relative transactivational capacities of estrone at the ERα and ERβ were 2.6% and 4.3% of those of estradiol, respectively. In accordance, the estrogenic activity of estrone has been reported to be approximately 4% of that of estradiol. Because estrone can be transformed into estradiol, which is far more potent as an estrogen in comparison, most of the estrogenic potency of estrone "in vivo" is actually due to conversion into estradiol. As such, similarly to the case of estrone sulfate, estrone is considered to be a prodrug of estradiol. Some "in vitro" research has suggested that estrone might be able to partially antagonize the actions of estradiol, but this does not appear to be of clinical significance.