Epitestosteron, eller isotestosteron, även känd som 17a-testosteron eller som androst-4-en-17a-ol-3-on, är en endogen steroid och en epimer av det androgena könshormonet testosteron. Det är en svag kompetitiv antagonist av androgenreceptorn (AR) och en potent 5a-reduktasinhibitor.
Strukturellt sett, epitestosteron skiljer sig från testosteron endast i konfigurationen vid det hydroxibärande kolet, 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; dock, by adulthood, most healthy males exhibit a testosterone to epitestosterone ratio (T/E ratio) of about 1:1
