Epitestosterone is a naturally occurring steroid hormone in the body, structurally similar to testosterone but biologically inactive. It does not exhibit the androgenic or anabolic effects that testosterone does. In the context of sports and doping control, the measurement of epitestosterone is significant. Normally, testosterone and epitestosterone are present in the body at a roughly 1:1 ratio. However, the administration of exogenous testosterone can disrupt this balance, leading to higher levels of testosterone relative to epitestosterone. Anti-doping agencies use the testosterone to epitestosterone (T/E) ratio as a marker to screen for the use of banned substances, including synthetic testosterone. A T/E ratio exceeding a certain threshold, typically above 4:1, may indicate the use of exogenous testosterone, prompting further investigation. The use of epitestosterone as a marker in doping tests underscores the importance of understanding the body's hormonal balance and the ways in which it can be altered by external substances. However, it's worth noting that various factors, including genetic differences, can naturally affect an individual's T/E ratio, which is considered in the evaluation process to ensure fairness and accuracy in doping control.