Selective Growth Hormone Secretagogue Receptor Agonism
Ipamorelin (NNC-26-0161) — Selective GHS-R Agonist
Ipamorelin (NNC-26-0161) is a synthetic pentapeptide and highly selective agonist of the growth hormone secretagogue receptor (GHS-R), also known as the ghrelin receptor. Developed by Novo Nordisk in the 1990s, ipamorelin was designed to stimulate growth hormone release with greater selectivity and a cleaner hormonal profile than earlier growth hormone-releasing peptides (GHRPs) such as GHRP-2 and GHRP-6.
The defining characteristic of ipamorelin in the research literature is its selectivity: unlike GHRP-2 and GHRP-6, which significantly elevate cortisol, prolactin, and ACTH alongside GH, ipamorelin stimulates GH release with minimal effect on these other hormones. This selectivity has made it a preferred research tool for studying the GH/IGF-1 axis in isolation.
Ipamorelin is a pentapeptide with the sequence Aib-His-D-2-Nal-D-Phe-Lys-NH2, where Aib is alpha-aminoisobutyric acid and D-2-Nal is D-2-naphthylalanine. These non-natural amino acid residues are critical to the compound's pharmacological profile: Aib at the N-terminus confers resistance to aminopeptidase degradation, while the D-amino acids at positions 3 and 4 prevent cleavage by endopeptidases and enhance GHS-R binding affinity.
The molecular weight is 711.85 Daltons, making ipamorelin one of the smallest GHS-R agonists. The C-terminal amide group is required for full receptor binding activity.
Ipamorelin acts as a selective agonist at the growth hormone secretagogue receptor (GHS-R1a), a G-protein coupled receptor expressed primarily on somatotroph cells in the anterior pituitary gland and on neurons in the hypothalamus. GHS-R1a activation by ipamorelin initiates a Gαq/11-mediated signaling cascade, increasing intracellular inositol trisphosphate (IP3) and diacylglycerol (DAG) levels, which in turn elevate intracellular calcium concentrations and activate protein kinase C (PKC).
This signaling cascade triggers the exocytosis of GH-containing secretory granules from somatotroph cells, producing a rapid, pulsatile GH release. Ipamorelin also attenuates the inhibitory effects of somatostatin on GH secretion, effectively amplifying the GH pulse. The resulting GH elevation stimulates hepatic IGF-1 production, which mediates the downstream anabolic effects.
Ipamorelin is a growth hormone secretagogue — a compound that stimulates the release of growth hormone from the pituitary gland. Unlike CJC-1295 (which mimics the 'go' signal from the hypothalamus), Ipamorelin mimics a different signal called ghrelin, often called the 'hunger hormone.' But Ipamorelin is engineered to trigger GH release without most of ghrelin's other effects.
Ipamorelin binds to the GHS-R1a receptor on pituitary cells — the same receptor that ghrelin uses — and triggers a pulse of growth hormone release. What makes it notable in research is its selectivity: it stimulates GH release without significantly raising cortisol, prolactin, or ACTH levels, which are common side effects of other GH secretagogues. This clean selectivity profile makes it a useful research tool for studying GH biology in isolation.
In research, Ipamorelin is often paired with CJC-1295 because they work through complementary pathways — CJC-1295 amplifies the GH pulse, while Ipamorelin triggers it. Together, they're studied as a way to produce a more robust GH response than either compound alone. The combination is one of the most discussed stacks in GH axis research.
Ipamorelin's standout quality is its selectivity — it's one of the cleanest GH secretagogues studied to date, with minimal effects on other hormonal axes. It's a research-only compound and is prohibited by WADA. Purgo Labs supplies it in research-grade lyophilized form for laboratory use only.
Binds GHS-R1a on pituitary somatotrophs, activating Gαq/11 → IP3/DAG → Ca²⁺ → PKC cascade that triggers GH exocytosis.
Reduces the inhibitory effect of somatostatin on GH secretion, amplifying the amplitude of GH pulses.
Secreted GH drives hepatic IGF-1 production, mediating downstream anabolic effects on muscle, bone, and metabolism.
GHS-R activation in the enteric nervous system modulates gastrointestinal motility, an area of active research investigation.
2 cited studies — model, sample size, outcome, and effect size from published literature.
| Study | Model | Sample | Outcome | Effect Size | Level |
|---|---|---|---|---|---|
Raun K, et al. (1998) Ipamorelin, the first selective growth hormone secretagogue PubMed | Rodent + human (Phase I) | Rodent: n=8–12/group; Human Phase I: n=24 | Selective GH release without significant cortisol, prolactin, or ACTH elevation | GH peak: 6–8× baseline; cortisol/prolactin: no significant change | Phase II |
Johansen PB, et al. (1999) Ipamorelin, a new growth-hormone-releasing peptide, induces longitudinal bone gr… PubMed | Rodent (rat) — tibial growth plate | n=30 | Significant increase in tibial growth plate width and longitudinal bone growth | ~15% increase in bone growth vs. control | Animal |
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| Peptide Class | Synthetic pentapeptide GHS-R agonist |
| Molecular Weight | 711.85 Da |
| Receptor Target | GHS-R1a (ghrelin receptor) |
| Key Selectivity | GH-specific; minimal cortisol/prolactin elevation |
| Available Sizes | 10mg vials |
| Form | Lyophilized powder |
| Purity | ≥99% (third-party tested) |
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Purchase Ipamorelin at Purgo LabsMedical Disclaimer: All content on this site is for educational and research purposes only. Research peptides are not FDA-approved for human use. Always consult a qualified healthcare professional before considering any peptide or supplement protocol. Nothing on this site constitutes medical advice, diagnosis, or treatment.
