Epiestriol (INN) (brand names Actriol, Arcagynil, Klimadoral), or epioestriol (BAN), also known as 16β-epiestriol or simply 16-epiestriol as well as 16β-hydroxy-17β-estradiol, is a minor and weak endogenous estrogen, and the 16β-epimer of estriol (which is 16α-hydroxy-17β-estradiol).