Estrone (medication)

Estrone (E1), sold under the brand names Estragyn, Kestrin, and Theelin among many others, is an estrogen medication and naturally occurring steroid hormone which has been used in menopausal hormone therapy and for other indications. It has been provided as an aqueous suspension or oil solution given by injection into muscle and as a vaginal cream applied inside of the vagina. It can also be taken by mouth as estradiol/estrone/estriol (brand name Hormonin) and in the form of prodrugs like estropipate (estrone sulfate; brand name Ogen) and conjugated estrogens (mostly estrone sulfate; brand name Premarin).

Side effects of estrogens like estrone include breast tenderness, breast enlargement, headache, nausea, fluid retention, and edema, among others. Estrone is a naturally occurring and bioidentical estrogen, or an agonist of the estrogen receptor, the biological target of estrogens like endogenous estradiol. It is a relatively weak estrogen, with much lower activity than estradiol. However, estrone is converted in the body into estradiol, which provides most or all of its estrogenic potency. As such, estrone is a prodrug of estradiol.

Estrone was first discovered in 1929, and was introduced for medical use shortly thereafter. Although it has been used clinically in the past, estrone has largely been discontinued and is mostly no longer marketed.