Ipamorelin: Structure, Selectivity and What the Research Shows
A pentapeptide built almost entirely from stability modifications, and the most selective growth hormone secretagogue described in the literature.
Ipamorelin is a five-residue synthetic peptide developed at Novo Nordisk in the 1990s and described in the literature as one of the most selective growth hormone secretagogues characterised. The selectivity is the reason it remains a reference compound in receptor pharmacology.
Structure
The sequence is Aib-His-D-2-Nal-D-Phe-Lys-NH2 — a pentapeptide with three non-standard features:
- Aib (α-aminoisobutyric acid) at the N-terminus, a non-proteinogenic residue that constrains backbone conformation and resists enzymatic cleavage
- D-amino acids at positions 3 and 4 — D-2-naphthylalanine and D-phenylalanine — which are not recognised by proteases evolved for L-residues
- C-terminal amidation, removing the free carboxylate and blocking carboxypeptidase attack
Molecular formula C38H49N9O5, molecular weight approximately 711.9 g/mol. Every one of those modifications exists to make a very short peptide survive longer than a very short peptide normally would.
Mechanism in the literature
Ipamorelin is an agonist at the growth hormone secretagogue receptor GHS-R1a — the same receptor ghrelin acts on. This places it in the GHRP class alongside GHRP-2 and GHRP-6, and distinct from GHRH analogues such as CJC-1295 and tesamorelin, which act through a different receptor entirely.
The finding that made it notable is selectivity. In the original characterisation work by Raun and colleagues (1998), ipamorelin released growth hormone with potency comparable to GHRP-6, but without the accompanying release of ACTH and cortisol seen with the earlier compounds in the class. Later work also reported minimal effect on prolactin.
That separation is what makes it useful as a research tool: it allows the GH axis to be probed with less confounding from adjacent endocrine responses.
GHRP versus GHRH — why the distinction matters
| GHRP class (ipamorelin) | GHRH class (CJC-1295, tesamorelin) | |
|---|---|---|
| Receptor | GHS-R1a | GHRH receptor |
| Endogenous ligand | Ghrelin | GHRH |
| Typical length | 5–6 residues | 29–44 residues |
| Release pattern in the literature | Pulsatile | Amplifies existing pulses |
Because the two classes act on separate receptors, studies frequently examine them in combination — which is why the pairing appears so often in the research literature.
Handling notes
A short, amidated peptide with no cysteine, no methionine and no tryptophan is at the stable end of the range. There is no disulfide to scramble and no primary photo-oxidation target. Standard practice applies: sealed lyophilised vials stored dry and cold, equilibrated to room temperature before opening, reconstituted with gentle swirling.
Analytically, a pentapeptide should give a clean chromatogram and an unambiguous mass. There is little room for a deletion sequence to hide in five residues, so a certificate showing a single dominant peak and a mass within a fraction of a dalton of 711.9 is exactly what to expect — and anything less tidy is worth questioning.
See our CJC-1295 versus ipamorelin comparison for the mechanistic contrast in more detail, and the certificate guide for reading the analytics.
Ipamorelin is supplied strictly for laboratory research. We do not provide dosing information and nothing here describes use in humans. Every batch is analysed by an independent laboratory for HPLC purity and mass-spectrometric identity, with batch-matched certificates available on request.
All products and information referenced are for in-vitro research and laboratory use only. Nothing here is medical advice, and no therapeutic claim is made or implied.