# What Is Ipamorelin Peptide? The Molecule Explained

> What is ipamorelin peptide? A selective growth-hormone secretagogue — a synthetic pentapeptide that releases a GH pulse via the ghrelin receptor without raising cortisol. The chemistry and evidence, cited.

The molecule, the receptor it works through, and why selectivity is its signature — built up from the chemistry to the skeletal evidence.

## The short answer

So, what is ipamorelin peptide, in plain words? It is a lab-made peptide — a short chain of five amino-acid building blocks — that tells the pituitary gland to release a pulse of growth hormone, the body's own signal for growth and repair [1]. It does this by acting on the ghrelin receptor, the same one the hunger hormone uses [1]. What sets it apart from older peptides in its family is precision: it raises growth hormone without meaningfully raising stress hormones like cortisol [1]. Researchers studied it most in bone, where in rats it sped up how fast long bones grew, in step with the dose [4]. It is not an approved medicine — its single human trial, for slow bowel recovery after surgery, did not work [3]. The rest of this page builds up from the chemistry to that evidence.

## The molecule and its sequence

Ipamorelin (also called NNC 26-0161; CAS 170851-70-4) is a synthetic pentapeptide — a chain of five amino acids — with the sequence Aib-His-D-2-Nal-D-Phe-Lys-NH2 [1]. Two design features matter. The first amino acid, Aib (alpha-aminoisobutyric acid), is a non-natural building block that makes the peptide more resistant to being broken down by enzymes; the D-form amino acids do the same. Together they give ipamorelin moderate metabolic stability — roughly five-fold lower plasma clearance than GHRP-6 in rats [5]. Its molecular formula is C38H49N9O5 and its weight is about 712 daltons (a unit for molecular mass) [1]. It was derived from an earlier peptide, GHRP-1, by removing a central dipeptide — a small chemical edit that produced a far more selective molecule.

## How it works: the ghrelin receptor

Ipamorelin works by activating the ghrelin / growth-hormone-secretagogue receptor (GHS-R1a) on the pituitary's growth-hormone-making cells [1]. The hunger hormone ghrelin is this receptor's natural key; ipamorelin is a synthetic mimic of that key. Turning the receptor produces a calcium signal inside the cell and a discrete pulse of growth hormone [1]. Because this is a different doorway than the GHRH receptor, ipamorelin's mechanism is complementary to GHRH analogs — which is why the two are studied together. The growth-hormone pulse can, in sustained settings, raise IGF-1 downstream, though short rodent studies often show no change in systemic IGF-1 even as local effects appear [4].

## Why selectivity is the whole point

The reason ipamorelin earned the title "the first selective growth hormone secretagogue" is that it separates the wanted effect from the unwanted ones [1]. In its 1998 characterization it released growth hormone potently in rat cells, rats, and pigs, yet did not raise ACTH, cortisol, or prolactin above baseline even at more than 200 times its growth-hormone threshold [1]. Older GH-releasing peptides such as GHRP-6 and GHRP-2 raise those hormones; ipamorelin largely does not. This selectivity is also why a study of [what is ipamorelin peptide](/what-is-ipamorelin) chemistry keeps returning to the same point — the molecule was engineered to be clean. That said, selective does not mean inert: it still acts on the ghrelin receptor's appetite and metabolic functions, which is why effects like hunger and the cautions on this site exist [12].

## What it is not

A few clarifications. Ipamorelin is not the CJC-1295 + ipamorelin combination — that is a research pairing of two separate peptides, and this page is about pure ipamorelin alone [3]. It is not an approved drug: no regulator has approved it for any indication, and its one Phase 2 trial missed its endpoint [3]. It is not a growth hormone itself — it prompts the body to release its own [1]. And it is not interchangeable with GHRH analogs like sermorelin or tesamorelin, which act on a different receptor entirely [1]. What it *is*: a selective, synthetic, ghrelin-receptor-acting GH secretagogue whose most quantitative evidence is the rodent skeletal record [4], with thin and largely negative human data [3].

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An md-desk reading of the ipamorelin record, led by the rat bone-growth data and kept honest about where the human evidence thins — every figure carried back to its study, no clinic behind the name and nothing dispensed.