Estradiol valerate is an estradiol ester, or a prodrug of estradiol.[15][4] As such, it is an estrogen, or an agonist of the estrogen receptors.[4][15] The affinity of estradiol valerate for the estrogen receptor is approximately 50 times lower than that of estradiol.[3] In addition, estradiol valerate is rapidly cleaved into estradiol and is unable to reach target tissues in concentrations of significance, if at all.[3] As such, estradiol valerate is essentially inactive in terms of estrogenic effect itself, acting solely as a prodrug to estradiol.[3] The molecular weight of estradiol valerate is about 131% of that of estradiol due to the presence of its C17β valerate ester, and hence estradiol valerate contains about 76% of the amount of estradiol of an equal dose of estradiol.[22][23] Aside from dose adjustment to account for the difference in molecular weight, oral estradiol valerate is considered to be equivalent to oral estradiol.[3] Because estradiol valerate is a prodrug of estradiol, it is considered to be a natural and bioidentical form of estrogen.[15][16][17]
Different estradiol routes and dosages can achieve widely varying circulating estradiol levels.[11] For purposes of comparison with normal physiological circumstances, menstrual cycle circulating levels of estradiol in premenopausal women are 40 pg/mL in the early follicular phase, 250 pg/mL at the middle of the cycle, and 100 pg/mL during the mid-luteal phase.[159] Mean integrated levels of circulating estradiol in premenopausal women across the whole menstrual cycle have been reported to be in the range of 80 and 150 pg/mL, according to some sources.[161][162][163]