Exogenous
Originating from outside the body and introduced through administration, as opposed to being naturally produced internally.
When a compound is administered exogenously — injected, inhaled, or otherwise introduced from outside — it enters biological systems that were designed for endogenous signals, potentially triggering the same receptors and pathways but at different concentrations or timing than what naturally occurs. Most research peptides are exogenous analogs of endogenous molecules.
The distinction between endogenous and exogenous matters for understanding feedback inhibition: introducing exogenous growth hormone, for example, can suppress the body’s own production through negative feedback. Researchers track exogenous administration schedules carefully to understand how compounds interact with the body’s baseline regulatory systems.