17β-Dihydroequilin is a naturally occurring estrogen sex hormone found in horses as well as a medication. As the C3 sulfate ester sodium salt, it is a minor constituent (1.7%) of conjugated estrogens (CEEs; brand name Premarin). 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.