# How Ipamorelin Works in the Research — Selectivity at GHS-R1a > What does ipamorelin peptide do? It selectively switches on the ghrelin receptor (GHS-R1a) to release a clean GH pulse without cortisol or prolactin. Fully cited. The selectivity story, step by step: one receptor, one clean GH pulse, almost nothing else. ## In plain English If you have ever wondered what does ipamorelin peptide do, here is the whole idea in a few sentences. Ipamorelin is a small lab-made peptide — five building blocks long — that lands on one specific docking site in the brain's hormone gland called GHS-R1a, the ghrelin receptor (the same site the body's natural 'hunger hormone' uses). When it docks there, the cell releases a quick burst of growth hormone (GH), the body's signal for repair and growth. The clever part is selectivity: it pulls the GH lever without pulling the levers for the stress hormone cortisol or the hormone prolactin. Older peptides in its family pulled all of those at once. Ipamorelin was the first to show you could separate them — releasing GH cleanly. The rest of this page walks through how that actually happens inside the cell, and why it matters. ## Step one: ipamorelin docks at the ghrelin receptor Ipamorelin is a selective agonist of GHS-R1a — the growth hormone secretagogue receptor type 1a, better known as the ghrelin receptor. An agonist is a molecule that switches a receptor on. This receptor sits on somatotrophs, the cells in the pituitary gland that store and release growth hormone. Ipamorelin's structure is built for this job: its sequence is Aib-His-D-2-Nal-D-Phe-Lys-NH2, where the unusual building blocks (an alpha-aminoisobutyric acid at one end, and two 'D-form' amino acids) make it resistant to the enzymes that would normally chew up a peptide [1]. It is a ghrelin mimetic — it copies what the body's natural ghrelin does at this receptor, but it was engineered for one purpose. ## Step two: the receptor fires a calcium cascade Once ipamorelin binds, the receptor activates a Gq/PLC signaling pathway inside the somatotroph. In plain terms, that pathway raises the level of calcium inside the cell, and the calcium surge is the trigger that pushes growth hormone out into the bloodstream [1]. A fish-pituitary study showed an important detail about this: ipamorelin released GH without increasing GH gene transcription even after 48 hours [11], which means it tells the cell to *release* the hormone it already has stored, rather than to manufacture more. The result is a fast, clean pulse — in humans, a single GH spike peaking about 40 minutes after dosing [2]. ## Step three: the selectivity — what it leaves untouched This is the part that made ipamorelin famous. Earlier growth-hormone-releasing peptides like GHRP-6 also stimulated ACTH and cortisol (the body's stress hormones) and prolactin. Ipamorelin does not raise ACTH or cortisol above the level seen with plain GHRH, even at doses more than 200 times higher than the dose needed for its GH effect [1]. In swine, its ED50 — the dose producing half the maximum GH effect — was 2.3 nmol/kg, comparable to GHRP-6's 3.9 nmol/kg, but without the off-target hormone output [1]. That clean separation of GH release from stress-hormone release is the single property the whole compound is known for. ## Why it pairs with GHRH analogs Ipamorelin releases GH through the ghrelin-receptor pathway, which is separate from the GHRH pathway. That separation is exactly why researchers combine it with GHRH analogs such as CJC-1295. When both pathways are engaged at once, the GH response is more than the sum of the parts: in rats, simultaneous GHRH and GHRP injection produced GH peaks significantly greater than the individual peaks added together [12]. Genetic models confirm the principle — in GHRH-knockout mice, a GHRP could only stimulate GH when GHRH was also present [14]. Two complementary switches, pulled together, open the gate wider than either alone. ## What it does beyond the pituitary GHS-R1a is not only on the pituitary. Ipamorelin's receptor also appears on enteric and vagal neurons (affecting gut motility), on pancreatic islet cells, and within hypothalamic appetite circuitry [1]. That broader distribution is why ipamorelin has been studied for postoperative ileus and chemotherapy-associated weight loss [3][5], and why appetite and a direct pancreatic insulin effect [18] show up as themes in its pharmacology. The headline remains the selective GH pulse — but the receptor's reach is what gives ipamorelin its wider research footprint. For the full study record, see [Ipamorelin research](/research). --- A forward-looking digest of what the ipamorelin literature actually measured — built around the peptide's selectivity, cited line by line, with nothing here dosed, prescribed, supplied, or sold.