Secretagogue

A secretagogue is a substance that triggers another substance to be secreted. In the peptide world, "secretagogue" almost always means a growth hormone secretagogue — something that causes the pituitary to release GH. There are two main pathways for doing this. GHRH agonists (like sermorelin, CJC-1295, and tesamorelin) mimic the hypothalamic signal that tells the pituitary to release GH. Ghrelin receptor agonists (like ipamorelin and GHRP-6) work through a different receptor — the same one that ghrelin (the hunger hormone) uses. The distinction matters because the two classes have different hormonal side-effect profiles. GHRH agonists tend to preserve the natural pulsatile pattern of GH release. Ghrelin receptor agonists can raise cortisol and prolactin in some compounds, though ipamorelin is selective enough to largely avoid this. What none of them do: directly replace growth hormone. They stimulate your pituitary to produce more of its own GH — so the ceiling is whatever your pituitary can still generate. In an older person with a less responsive pituitary, that ceiling is lower than in someone younger.