Endogenous.

Produced naturally within the body.

Endogenous compounds are made by the organism itself, as opposed to exogenous compounds introduced from outside. Endogenous GLP-1 is the hormone your gut releases after a meal; an injected GLP-1 receptor agonist is exogenous. The distinction carries more weight in peptide research than it might seem. Endogenous hormones are typically released in tightly controlled patterns, in small amounts, at particular times, and are cleared within minutes, with feedback loops that shut production off when levels rise. Exogenous versions bypass much of that control, which is precisely what makes them useful as drugs and also what creates the risk of overshooting a system that was designed to self-regulate. The related idea is negative feedback: supplying a hormone from outside can reduce the body's own production of it, and in some axes that suppression can persist after the exogenous compound is stopped. The misunderstanding worth correcting is the assumption that because a molecule is identical to something the body already makes, it must be inherently safe. Route, amount, and timing all differ from the natural pattern, and identical chemistry delivered on a different schedule is not the same physiological event.