Administered from outside the body — whether injected, swallowed, or applied to skin.The distinction between endogenous and exogenous matters because the body regulates its own peptide production through feedback loops that exogenous administration bypasses or disrupts. Exogenous GH secretagogues cause GH release in a pattern determined by injection timing rather than physiological demand. Exogenous oxytocin in pharmacological doses activates receptors in tissues that endogenous oxytocin never reaches in those concentrations. "Natural" is not the same as "safe at pharmacological doses."F↑ Top