Definition
What Is Ipamorelin? The Peptide Explained
A synthetic pentapeptide, a selective ghrelin-receptor agonist, and the original proof that GH release could be made clean.
The short answer
So what is ipamorelin peptide, in one read? It is a small synthetic peptide — just five amino acids — designed in the 1990s to make the body release growth hormone (GH), the signal for repair and growth. It works by switching on one specific receptor, the ghrelin receptor (called GHS-R1a), on the gland that stores GH. Its claim to fame is selectivity: it triggers GH while leaving the stress hormone cortisol and the hormone prolactin essentially alone, which the older peptides could not do. It is wholly lab-made, not something your body produces, and it copies the action of ghrelin, the natural 'hunger hormone'. Importantly, ipamorelin has never been approved as a medicine anywhere — it is a research compound with a clear mechanism and a thin human track record.
The molecule itself
Ipamorelin (development code NNC 26-0161) is a synthetic pentapeptide — a chain of five amino acids — with the sequence Aib-His-D-2-Nal-D-Phe-Lys-NH2. The alpha-aminoisobutyric acid at position one and the D-form amino acids are deliberate: they make the peptide resistant to the enzymes that normally break peptides down [1]. Its molecular formula is C38H49N9O5, with a molecular weight of about 711.85 daltons and CAS number 170851-70-4. It was derived from the earlier peptide GHRP-1 by removing a central dipeptide. It is wholly synthetic — not an endogenous human peptide — and it acts as a ghrelin mimetic, copying ghrelin's action at the GHS-R1a receptor [1].
What class of compound it belongs to
Ipamorelin is a growth hormone secretagogue — a compound that prompts the pituitary to secrete GH — and more specifically a GHS-R1a (ghrelin-receptor) agonist. It belongs to the GHRP (growth-hormone-releasing peptide) family, which also includes GHRP-2 and GHRP-6, and which is mechanistically distinct from GHRH analogs like sermorelin, tesamorelin, and CJC-1295 [1]. Within its own family, ipamorelin is the selective one: it was the first GHS shown to release GH potently without the cortisol, ACTH, and prolactin elevation that accompanied its predecessors [1]. That distinction — same family, far cleaner profile — is the reason it became the reference compound for selective GH release.
What the research has shown it does
In its founding characterization, ipamorelin released GH potently in rat pituitary cells, anaesthetised rats, and conscious swine, with a swine ED50 of 2.3 nmol/kg, while leaving ACTH and cortisol unraised even at more than 200 times that dose [1]. In humans, a small PK study found a terminal half-life of about 2 hours and a single GH pulse peaking around 40 minutes after dosing [2]. In rats, it dose-dependently increased longitudinal bone growth without changing systemic IGF-1 [4]. Its one Phase 2 human trial, for postoperative ileus, missed its primary endpoint [3]. And in a 2024 ferret study it reduced chemotherapy-associated weight loss by about 24% [5]. The pattern is a precise, selective tool with reproducible animal signals and a still-thin human record — which is exactly what does ipamorelin peptide do in mechanistic detail.
What it is not
Ipamorelin is not an approved drug — it has never been approved by the FDA, EMA, or any regulatory body for any indication [3]. It is not the same thing as the CJC-1295 plus ipamorelin combination; ipamorelin is a single peptide, while that 'stack' is two peptides used together. It is not a GHRH analog — it works on a different receptor than sermorelin or tesamorelin [1]. It is not orally active in its native form; only engineered analogs derived from it achieved meaningful oral bioavailability [8]. And it is prohibited in sport at all times under WADA category S2. Ipamorelin is, precisely, a research-grade selective growth hormone secretagogue — no more and no less.