Estrogen (medication)
Estradiol, estrone, and estriol have all been approved as pharmaceutical drugs and are used medically. Estetrol is currently under development for medical indications, but has not yet been approved in any country. A variety of synthetic estrogen esters, such as estradiol valerate, estradiol cypionate, estradiol acetate, estradiol benzoate, estradiol undecylate, and polyestradiol phosphate, are used clinically. The aforementioned compounds behave as prodrugs to estradiol, and are much longer-lasting in comparison when administered by intramuscular or subcutaneous injection. Esters of estrone and estriol also exist and are or have been used in clinical medicine, for example estrone sulfate (e.g., as estropipate), estriol succinate, and estriol glucuronide (as Emmenin and Progynon).
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.