Synthetic replicas of endogenous steroids are both chemically and pharmacologically indistinguishable from their natural counterparts. By examining isotopes within these steroids, distinct isotope fingerprints emerge in urinary samples, creating a reliable discrimination framework. Explore the concept of Isotope Fingerprints and their application in doping control investigations. Discover how these fingerprints play a crucial role in distinguishing between naturally produced (endogenous) and ext