What Is Ipamorelin?
Ipamorelin is a synthetic pentapeptide growth hormone secretagogue (GHS) with the sequence Aib-His-D-2-Nal-D-Phe-Lys-NH₂. First characterised in the late 1990s by researchers at Novo Nordisk, it belongs to the growth hormone-releasing peptide (GHRP) class but is distinguished by a selectivity profile that sets it apart from earlier compounds in that family. Ipamorelin stimulates growth hormone (GH) release without significant elevation of cortisol, prolactin, or ACTH — a pharmacological characteristic that has made it a widely used research tool for studying the GH axis in isolation.
As a ghrelin receptor agonist acting at GHSR-1a, Ipamorelin mimics aspects of the endogenous ghrelin signalling pathway within the pituitary, producing dose-dependent, pulsatile GH secretion consistent with physiological patterns. This combination of selectivity and predictable pharmacokinetics has established Ipamorelin as a standard reference compound in growth hormone secretagogue research.
Molecular Profile
- Class: Pentapeptide growth hormone-releasing peptide (GHRP)
- Sequence: Aib-His-D-2-Nal-D-Phe-Lys-NH₂
- Molecular weight: approximately 711.86 Da
- CAS number: 170851-70-4
- Receptor target: GHSR-1a (growth hormone secretagogue receptor type 1a / ghrelin receptor)
- Half-life (preclinical): approximately 2 hours in rodent models
- Supplied as: lyophilised powder for in vitro research use
Mechanism of Action: GHSR-1a Agonism
Ipamorelin functions as a selective agonist at GHSR-1a, a G-protein coupled receptor (GPCR) expressed predominantly on anterior pituitary somatotrophs and, to a lesser extent, in peripheral tissues including the gastrointestinal tract. GHSR-1a is the canonical receptor for the endogenous hormone ghrelin; Ipamorelin mimics ghrelin’s agonist activity at this receptor without replicating its full hormonal profile.
Upon binding GHSR-1a, Ipamorelin initiates the following intracellular signalling cascade:
- Gq/11 pathway activation: Receptor occupancy couples to Gq/11 heterotrimeric G-proteins, activating phospholipase C beta (PLC-β)
- Second messenger generation: PLC-β cleaves phosphatidylinositol 4,5-bisphosphate (PIP₂) into inositol trisphosphate (IP₃) and diacylglycerol (DAG)
- Calcium mobilisation: IP₃ triggers calcium release from the endoplasmic reticulum, elevating intracellular [Ca²⁺] and promoting GH secretory granule exocytosis from somatotrophs
- PKC activation: DAG activates protein kinase C (PKC), contributing to GH gene transcription and sustaining secretory responses over longer timescales
- Pulsatile GH release: The net effect is dose-dependent, pulsatile GH secretion that closely mirrors physiological GH rhythm — an important characteristic for research into somatotroph biology and GH pulse dynamics
A key feature of Ipamorelin’s mechanism is its selectivity. Unlike GHRP-2 and GHRP-6, which significantly activate ACTH, cortisol, and prolactin pathways alongside GH release, Ipamorelin produces minimal off-target stimulation of these axes at equivalent GH-releasing doses. This was first formally demonstrated by Raun et al. (1998) in a study published in European Journal of Endocrinology, which established Ipamorelin’s pharmacological profile as a high-selectivity GH secretagogue suitable for studies requiring isolated GH pathway activation.
Key Research Areas
GH Axis Regulation and Somatotroph Biology
Ipamorelin is used extensively as a research tool in studies of somatotroph function, GH pulse characteristics, and GHSR-1a receptor pharmacology. Its predictable, pulsatile GH-releasing action and minimal side-axis activity make it well suited for in vitro cell culture models and preclinical in vivo studies where isolated GH pathway stimulation is a methodological requirement. Research has examined receptor desensitisation dynamics, dose-response relationships, and the interaction of GHSR-1a agonism with somatostatin-mediated GH inhibition.
Bone Density and Skeletal Biology
Several preclinical studies have examined Ipamorelin’s effects on osteoblast activity and bone mineral density in animal models. Svensson et al. (2000), in a study conducted using ovariectomised rat models of postmenopausal bone loss, demonstrated statistically significant increases in bone mass following Ipamorelin administration. The authors attributed these effects to GH-dependent and, potentially, direct GHSR-1a-mediated stimulation of osteoblast proliferation. This finding has provided a basis for ongoing skeletal biology research examining GH secretagogues in models of bone remodelling and density maintenance.
Metabolic Research
Growth hormone plays a central role in regulating lipolysis, glucose metabolism, lean mass composition, and IGF-1 production in the liver. Ipamorelin has been employed in metabolic research models examining GH’s downstream effects on these parameters, including adipogenesis, nitrogen balance, and insulin-like growth factor signalling. Its selectivity profile reduces the confounding influence of cortisol — a counter-regulatory metabolic hormone — that complicates interpretation in studies using less selective GHRPs.
Gastrointestinal Motility Research
GHSR-1a receptors are expressed throughout the gastrointestinal tract, where ghrelin signalling contributes to motility regulation. Helsinn Therapeutics conducted Phase II/III clinical trials investigating Ipamorelin for postoperative ileus (POI) — a condition characterised by impaired GI motility following abdominal surgery. These trials demonstrated that Ipamorelin produced measurable prokinetic effects mediated via peripheral GHSR-1a receptor activation, distinct from its central pituitary GH-releasing action. While the POI indication was not commercially developed, the trial data contribute to the peer-reviewed literature on GHSR-1a physiology in the gastrointestinal system.
Appetite Regulation and Energy Homeostasis
As a ghrelin receptor agonist, Ipamorelin has been used in models examining GHSR-1a’s role in appetite regulation and energy balance. Its effects on food intake are less pronounced than those of acylated ghrelin itself, but research has used Ipamorelin as a probe compound to dissect the receptor’s contribution to orexigenic signalling, hypothalamic feeding circuits, and energy homeostasis parameters in preclinical models.
Ipamorelin Compared to Related Growth Hormone Secretagogues
Understanding Ipamorelin’s position relative to other compounds in the GHS research field is important for experimental design. The following comparison covers the peptides most frequently referenced alongside Ipamorelin in the research literature.
Ipamorelin vs GHRP-6
GHRP-6 was one of the first synthetic GHRPs to be characterised (Bowers et al., 1980s) and remains a reference compound in GHS research. Both peptides act at GHSR-1a, but GHRP-6 produces significant elevations in cortisol, prolactin, and ACTH alongside GH release — effects that can confound metabolic and endocrine research models. Ipamorelin’s superior selectivity makes it the preferred tool where isolated GH pathway study is the goal. GHRP-6 also produces a pronounced increase in appetite via ghrelin-mimetic orexigenic signalling, more marked than Ipamorelin.
Ipamorelin vs GHRP-2
GHRP-2 is a more potent GH releaser than Ipamorelin on a molar basis and produces higher peak GH concentrations in rodent models. However, like GHRP-6, it significantly elevates cortisol and ACTH, limiting its utility in studies requiring selective GH pathway activation. Ipamorelin is generally preferred for studies where hormonal side-axis effects would compromise data interpretation, while GHRP-2 may be selected where maximal GH stimulation is the primary experimental objective regardless of selectivity.
Ipamorelin vs Sermorelin (GHRH 1-29)
Sermorelin is a synthetic analogue of endogenous growth hormone-releasing hormone (GHRH), acting at the GHRH receptor (GHRHR) rather than GHSR-1a. Where Ipamorelin mimics ghrelin’s receptor pathway, Sermorelin mimics the hypothalamic GHRH signal. The two compounds act on distinct upstream components of the GH secretion pathway, and their co-administration in preclinical models has been studied for potential synergistic effects. Sermorelin has a shorter half-life and is subject to more rapid degradation than some modified GHRH analogues.
Ipamorelin vs CJC-1295 No DAC (MOD GRF 1-29)
CJC-1295 No DAC is a 29-amino acid GHRH analogue that, like Sermorelin, acts at the GHRHR rather than GHSR-1a. Its four amino acid substitutions versus native GHRH confer improved enzymatic stability and an approximately 30-minute half-life in preclinical models. The combination of Ipamorelin (GHSR-1a agonist) and CJC-1295 No DAC (GHRHR agonist) targets two distinct receptor populations in the GH secretion pathway, and preclinical research has demonstrated synergistic GH release exceeding that of either compound alone when both peptides are co-administered — a finding that has made this combination a standard approach in GH axis research models. R&D Peptides supplies both compounds individually and as a combination research pen for studies requiring dual-pathway activation.
Research Status and Clinical Investigation
Ipamorelin has progressed further through formal clinical investigation than most peptides in the GHRP class. Helsinn Therapeutics conducted Phase II and Phase III trials in postoperative ileus, generating human safety and pharmacokinetic data in controlled research settings. These trials established that Ipamorelin was well tolerated in human subjects at doses studied and demonstrated measurable GI motility effects via peripheral GHSR-1a receptor mechanisms. The compound did not proceed to regulatory approval for POI, but the trial data — published in peer-reviewed form — represent an important contribution to the GHS research literature.
Beyond the Helsinn data, the preclinical literature on Ipamorelin spans GH axis pharmacology, bone biology, metabolic modelling, and receptor characterisation. The compound has a well-characterised receptor pharmacology and predictable dose-response relationship in rodent models, providing a robust research foundation. Independent replication of key findings across multiple research groups is more established for Ipamorelin than for many other research peptides in this class.
Key Takeaways
- Ipamorelin is a synthetic pentapeptide GH secretagogue (sequence: Aib-His-D-2-Nal-D-Phe-Lys-NH₂; MW ~711.86 Da) that acts as a selective GHSR-1a agonist.
- Its defining pharmacological feature is selectivity: GH release without significant co-stimulation of cortisol, prolactin, or ACTH axes, unlike GHRP-2 and GHRP-6.
- Mechanism involves Gq/11 signalling, PLC activation, intracellular calcium mobilisation, and pulsatile GH secretory granule exocytosis from pituitary somatotrophs.
- Key preclinical research areas include GH axis pharmacology, bone mineral density, metabolic modelling, and GI motility studies.
- Helsinn Therapeutics conducted Phase II/III human clinical trials for postoperative ileus, establishing a documented human safety profile in controlled settings.
- Ipamorelin is frequently combined with CJC-1295 No DAC in dual-pathway GH research models, targeting GHSR-1a and GHRHR simultaneously.
Sourcing Ipamorelin for Research
R&D Peptides supplies Ipamorelin 10mg as a lyophilised research compound accompanied by a batch-specific Certificate of Analysis confirming purity by HPLC and molecular weight by mass spectrometry. Also available as an Ipamorelin 10mg / CJC-1295 No DAC 5mg Combination Pen for research applications requiring dual-pathway GH axis stimulation. All compounds are supplied strictly for in vitro research use only.
For related research, see our guides on CJC-1295 No DAC, TB-500, and BPC-157.
For quality and testing standards, see our quality and testing page.
Frequently Asked Questions
What distinguishes Ipamorelin from other growth hormone-releasing peptides?
Ipamorelin’s primary distinguishing characteristic is its selectivity for GH release. Unlike GHRP-2 and GHRP-6, which significantly elevate cortisol, ACTH, and prolactin alongside GH, Ipamorelin produces minimal stimulation of these axes at equivalent GH-releasing doses. This was first formally established by Raun et al. (1998), and the finding has been reproduced across multiple preclinical studies. For research models requiring isolated GH axis stimulation, Ipamorelin is the most widely used reference compound in the GHRP class.
How does Ipamorelin interact with CJC-1295 No DAC in research models?
Ipamorelin acts at GHSR-1a (the ghrelin receptor) on pituitary somatotrophs, while CJC-1295 No DAC acts at the GHRH receptor (GHRHR) on the same cell population. Because the two peptides target distinct receptor pathways that converge on GH secretory machinery, their co-administration in preclinical models produces synergistic GH release exceeding that of either compound alone. This dual-receptor approach is a standard methodology in GH axis research.
Has Ipamorelin been studied in human subjects?
Yes. Helsinn Therapeutics conducted Phase II and Phase III clinical trials investigating Ipamorelin for postoperative ileus (POI). These trials generated human pharmacokinetic and safety data in controlled clinical settings, making Ipamorelin one of the better-characterised synthetic GHRPs with respect to human research data. The compound was not commercially approved for the POI indication, but the peer-reviewed trial publications contribute meaningfully to the research literature.
What does GHSR-1a stand for and where is it expressed?
GHSR-1a stands for growth hormone secretagogue receptor type 1a, also termed the ghrelin receptor. It is predominantly expressed on anterior pituitary somatotrophs, where it mediates GH release, but is also found in the hypothalamus, hippocampus, brainstem, and throughout the gastrointestinal tract. Peripheral GHSR-1a expression underlies Ipamorelin’s prokinetic effects observed in the postoperative ileus trial data.
Where can researchers source Ipamorelin in the UK?
R&D Peptides supplies research-grade Ipamorelin 10mg in the UK, verified by HPLC at ≥98% purity and accompanied by a batch-specific Certificate of Analysis. All compounds are for laboratory research use only and are not intended for human administration.
All content on this page is for educational and informational purposes only. Ipamorelin is supplied by R&D Peptides strictly for in vitro research use. It is not intended for human or veterinary administration, and no therapeutic claims are made or implied.
