17β-Dihydroequilin is a naturally occurring estrogen sex hormone found in horses as well as a medication.

[1][2] As the C3 sulfate ester sodium salt, it is a minor constituent (1.7%) of conjugated estrogens (CEEs; brand name Premarin).

[1] However, as equilin, with equilin sulfate being a major component of CEEs, is transformed into 17β-dihydroequilin in the body, analogously to the conversion of estrone into estradiol, 17β-dihydroequilin is, along with estradiol, the most important estrogen responsible for the effects of CEEs.

[1] In terms of relative binding affinity for the ERs, 17β-dihydroequilin has about 113% and 108% of that of estradiol for the ERα and ERβ, respectively.

[1] 17β-Dihydroequilin, or simply β-dihydroequilin, also known as δ7-17β-estradiol or as 7-dehydro-17β-estradiol, as well as estra-1,3,5(10),7-tetraen-3,17β-diol, is a naturally occurring estrane steroid and an analogue of estradiol.