Estradiol (medication)
, estradiol is available in the United States in the following forms:Oral estradiol valerate (Progynova) and other esters of estradiol that are used by injection like estradiol benzoate, estradiol enantate, and estradiol undecylate all are not marketed in the U.S. Polyestradiol phosphate (Estradurin) was marketed in the U.S. previously but is no longer available.
Estriol
Although estriol is an efficacious agonist of the ERs, it is reported to have mixed agonist–antagonist (partial agonist) activity at the ER; on its own, it is weakly estrogenic, but in the presence estradiol, it is antiestrogenic. Given by subcutaneous injection in mice, estradiol is about 10-fold more potent than estrone and about 100-fold more potent than estriol. It is notable that unlike estriol, estrone can be metabolized into estradiol, and most of its potency "in vivo" is in fact actually due to conversion into estradiol.