Epitestosteroon, of isotestosteroon, ook bekend as 17α-testosteroon of as androst-4-en-17α-ol-3-one, is 'n endogene steroïde en 'n epimeer van die androgeen geslagshormoon testosteroon. Dit is 'n swak kompeterende antagonis van die androgeenreseptor (AR) en 'n kragtige 5α-reduktase inhibeerder.
Struktureel, epitestosteroon verskil slegs van testosteroon in die konfigurasie by die hidroksie-draende koolstof, C17. Epitestosterone is believed to form in a similar way to testosterone; a 1993 study found that around 50% of epitestosterone production in human males can be ascribed to the testis, although the exact pathway of its formation is still the subject of research. It has been shown to accumulate in mammary cyst fluid and in the prostate.Epitestosterone levels are typically highest in young males; egter, by adulthood, most healthy males exhibit a testosterone to epitestosterone ratio (T/E ratio) of about 1:1
