Ipamorelin is a synthetic pentapeptide growth hormone secretagogue and selective agonist of the ghrelin receptor (GHS-R1a). Developed in the 1990s as part of a systematic effort to improve on the selectivity profile of earlier GHRP compounds, Ipamorelin represented a significant advance in GH secretagogue pharmacology: it produces robust, dose-dependent GH release with minimal stimulation of cortisol, ACTH, or prolactin — hormones that earlier GHRPs elevated as secondary effects. This selectivity has made Ipamorelin one of the most widely used research peptides for studying the GH axis in isolation.
For researchers investigating pituitary GH secretion dynamics, the downstream metabolic effects of GH/IGF-1 axis activation, or the pharmacology of the ghrelin receptor system, Ipamorelin provides a clean, well-characterized tool compound with a substantial published literature across preclinical and early clinical research settings.
Ipamorelin (Aib-His-D-2-Nal-D-Phe-Lys-NH₂) is a pentapeptide containing a non-natural alpha-aminoisobutyric acid (Aib) residue at the N-terminus and a D-2-naphthylalanine residue at position 3 — substitutions that confer proteolytic stability and define its receptor interaction geometry. It was developed by Novo Nordisk and first described in the peer-reviewed literature in 1998 by Raun et al., who documented its potent, selective GH-releasing activity in porcine and rat models.
Unlike full-length ghrelin (28 amino acids) or the earlier hexapeptide GHRPs, Ipamorelin’s compact five-residue structure represents the minimum pharmacophore required for high-affinity GHS-R1a agonism. Its plasma half-life of approximately 2 hours is longer than most other GHRPs, and it is supplied as a white lyophilized powder that reconstitutes readily in sterile bacteriostatic water for research applications.
| Property | Value |
|---|---|
| Full name | Ipamorelin |
| Also known as | NNC 26-0161 |
| Amino acid sequence | Aib-His-D-2-Nal-D-Phe-Lys-NH₂ |
| Molecular formula | C₃₈H₄₉N₉O₅ |
| Molecular weight | 711.86 g/mol |
| CAS number | 170851-70-4 |
| Purity (Official Peptides) | >99% by HPLC |
| Physical form | White lyophilized powder |
| Solubility | Water soluble |
| Half-life (plasma) | ~2 hours |
| Storage (lyophilized) | 2–8°C, protected from light |
| Storage (reconstituted) | 4°C, use within 30 days |
The defining pharmacological characteristic of Ipamorelin is its selective activation of GHS-R1a with minimal downstream stimulation of ACTH/cortisol or prolactin. The original characterization study by Raun et al. (1998) established that Ipamorelin, unlike GHRP-2 and GHRP-6 at equivalent GH-stimulating doses, produced no statistically significant cortisol or ACTH elevation in swine and rat models. This selectivity was subsequently confirmed in multiple independent research groups across species.
The mechanistic basis of this selectivity is not fully resolved, but research has pointed to differences in GHS-R1a coupling efficiency to distinct G-protein populations and second messenger cascades in somatotrophs versus corticotrophs. Ipamorelin’s compact pentapeptide structure appears to engage a specific subset of receptor conformations that preferentially activate the somatotroph secretory apparatus without recruiting the broader receptor signaling pathways that ACTH-stimulating GHRPs activate.
For researchers, this selectivity means that GH-driven experimental outcomes can be attributed specifically to GH pathway activation rather than to corticosteroid or prolactin effects — a significant advantage in any study where these hormones have known effects on the experimental endpoints being measured.
Research has characterized Ipamorelin’s effects on the pattern as well as the magnitude of GH secretion. Like endogenous ghrelin, Ipamorelin amplifies pulsatile GH release rather than producing sustained GH elevation — preserving the physiological rhythmicity of GH secretion that is important for downstream tissue responses. Studies using frequent blood sampling in rodent models have documented that Ipamorelin increases GH pulse amplitude without altering pulse frequency, producing a pattern of GH secretion that more closely resembles physiological GH dynamics than continuous GH infusion or long-acting GHRH analogues.
This pulsatile GH-stimulating profile is considered advantageous by researchers studying the physiological consequences of GH elevation, since many GH target tissues respond differently to pulsatile versus continuous GH exposure. Hepatic IGF-1 production, for example, is regulated in a pulse-pattern-dependent manner, and research designs that require physiologically relevant IGF-1 responses benefit from the pulsatile GH secretion profile that Ipamorelin preserves.
One of the most consistently replicated findings in Ipamorelin research is the synergistic GH response when Ipamorelin is combined with GHRH receptor agonists such as Sermorelin, CJC-1295 No DAC, or CJC-1295 DAC. Research has documented that simultaneous activation of both the GHS-R1a pathway (via Ipamorelin) and the GHRHR pathway (via GHRH analogues) produces GH secretory responses substantially greater than the sum of either stimulus alone.
The mechanistic basis for this synergy has been examined in pituitary cell culture systems. GHS-R1a activation via Ipamorelin increases intracellular calcium through IP3-mediated release, while GHRHR activation increases cAMP through Gs coupling — two complementary intracellular signals that converge on GH exocytosis. When both pathways are activated simultaneously, the calcium and cAMP signals amplify each other’s effect on the GH secretory machinery, producing the supra-additive GH response observed experimentally.
This synergy has practical implications for research designs: lower doses of each compound can be used in combination while achieving GH responses comparable to maximal single-compound doses, reducing potential off-target effects and improving dose-response resolution in combination studies.
The GH/IGF-1 axis has well-established effects on body composition — promoting lean mass accretion through IGF-1-driven protein synthesis and stimulating lipolysis through direct GH effects on adipocytes. Research has used Ipamorelin’s selective GH-stimulating profile to examine these body composition effects in isolation from the confounding hormonal changes (particularly cortisol elevation) that complicate interpretation of results with less selective GHRP compounds.
Studies in rodent models have documented Ipamorelin-associated increases in lean body mass and reductions in fat mass over multi-week treatment periods. Research examining the dose-response relationship between Ipamorelin-induced GH elevation and IGF-1 responses has characterized the dynamic range of the GH-IGF-1 axis under pharmacological stimulation — findings relevant to researchers studying the metabolic consequences of GH secretagogue administration.
GH secretion declines progressively with age — a process termed the somatopause — and research has examined whether pharmacological restoration of GH pulse amplitude through secretagogues like Ipamorelin can attenuate age-related changes in body composition, bone density, and metabolic function. Ipamorelin’s selective profile makes it particularly suitable for somatopause research, as cortisol elevation (which older GHRP compounds produce) itself drives adverse changes in body composition and bone density that would confound the interpretation of GH-restorative effects.
Preclinical studies in aged rodents have documented Ipamorelin-associated improvements in lean mass, bone mineral density markers, and cortical bone thickness compared to vehicle controls. These findings have supported research interest in selective GH secretagogues as tools for studying the biology of somatopause and as potential interventions in GH-deficient aging models.
The ghrelin receptor (GHS-R1a) is a constitutively active Class A GPCR with high basal signaling activity even in the absence of ligand. It couples to multiple G-protein subtypes — primarily Gq/11 for calcium signaling, but also Gs and G12/13 in different cell types — and activates arrestin-mediated internalization pathways following agonist binding. Different GHS-R1a agonists can bias receptor signaling toward different coupling pathways, a phenomenon known as functional selectivity or biased agonism.
Research suggests that Ipamorelin’s compact structure produces biased GHS-R1a activation that favors Gq/11-mediated calcium signaling in somatotrophs over the alternative pathways that GHRP-6 and other earlier GHRPs also engage. This biased agonism explains why Ipamorelin produces GH release comparable to older GHRPs while avoiding their off-target hormonal effects — it activates the specific receptor signaling pathway relevant to GH secretion more efficiently than the pathways that drive ACTH and prolactin release.
Understanding this receptor selectivity mechanism is not merely of academic interest: it has guided the design of next-generation GH secretagogues and has made Ipamorelin a benchmark compound for GHRP selectivity studies in receptor pharmacology research.
Non-natural amino acid stability: Ipamorelin’s D-amino acid residues at positions 3 and 4 confer resistance to proteolytic degradation compared to all-L-amino acid peptides. This stability is advantageous for in vitro research in serum-containing media and for in vivo studies where peptide stability at the site of administration is a concern.
Somatostatin tone: Ipamorelin’s GH-stimulating effect, like all GHS-R1a agonists, is modulated by endogenous somatostatin tone. Studies conducted during periods of high somatostatin activity will show attenuated GH responses. Standardizing administration timing relative to circadian somatostatin cycles improves response reproducibility.
Combination protocol design: When using Ipamorelin in combination with GHRH analogues, dose selection requires careful titration — the synergistic GH response means that combination doses producing equivalent GH elevation to monotherapy are substantially lower than monotherapy doses. Review published combination protocols before designing dose levels for new experiments.
Storage: Lyophilized Ipamorelin is stable at 2–8°C for up to 24 months. Reconstituted solutions should be stored at 4°C and used within 30 days. Prepare aliquots to avoid repeated freeze-thaw of reconstituted material.
Official Peptides supplies research-grade Ipamorelin at >99% purity confirmed by HPLC and mass spectrometry, with batch-specific certificates of analysis available for every purchase. We maintain consistent US-based inventory and ship cold-pack with same-day dispatch on qualifying orders. Ipamorelin is available individually or as part of our combination peptide catalog alongside CJC-1295 and other GHRH pathway compounds.
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Official Peptides supplies research-grade Ipamorelin with >99% HPLC purity and batch-specific COA included. US domestic shipping 2–5 business days. For in vitro research use only.
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