Equilin is a naturally occurring estrogen sex hormone found in horses as well as a medication.

[2][3] CEEs is the most commonly used form of estrogen medications in hormone replacement therapy (HRT) for menopausal symptoms in the United States.

[2] In terms of relative binding affinity for the ERs, equilin has about 13% and 49% of that of estradiol for the ERα and ERβ, respectively.

[2] Analogously to the reversible transformation of estrone into estradiol by 17β-hydroxysteroid dehydrogenase, equilin can be converted into the more potent estrogen 17β-dihydroequilin in the body.

[2] A dosage of 0.25 mg/day equilin sulfate is equivalent to 0.625 mg/day CEEs in terms of relief from hot flashes.