Quick answer: Ipamorelin is a synthetic pentapeptide (Aib-His-D-2-Nal-D-Phe-Lys-NH2) and the first truly selective growth hormone-releasing peptide (GHRP). It activates the GHS-R1a ghrelin receptor on pituitary somatotrophs to trigger pulsatile GH release, but unlike earlier GHRPs such as GHRP-6, GHRP-2, and hexarelin it does not meaningfully elevate cortisol, ACTH, or prolactin in published preclinical work. This guide covers ipamorelin’s mechanism, receptor selectivity, half-life, stacking rationale with GHRH analogs like CJC-1295, and preclinical study protocols. For research purposes only. Not for human consumption.
What is ipamorelin?
Ipamorelin (code name NNC 26-0161) is a synthetic pentapeptide that was first described in the late 1990s by researchers at Novo Nordisk. Chemically it is Aib-His-D-2-Nal-D-Phe-Lys-NH2, an unnatural-residue peptide designed to hit the ghrelin receptor selectively while leaving adjacent signaling pathways alone. Its intended purpose at the time of discovery was to serve as a research tool for studying growth hormone secretion and pituitary function in animal models.
In the growth hormone literature, peptides that stimulate GH release are split into two mechanistic classes. GHRH analogs (sermorelin, tesamorelin, CJC-1295) mimic endogenous growth hormone-releasing hormone and act on the GHRH receptor. GHRPs (growth hormone-releasing peptides) such as GHRP-2, GHRP-6, hexarelin, and ipamorelin instead act on the GHS-R1a ghrelin receptor. Ipamorelin sits firmly in the GHRP class. It is not a GHRH analog, a SARM, or a true ghrelin mimetic despite sharing a receptor with ghrelin. For a broader map of the GH peptide family, see our sermorelin research guide and the tesamorelin pillar.
Mechanism of action: GHS-R1a activation and GH pulse pharmacology
Ipamorelin binds the growth hormone secretagogue receptor type 1a (GHS-R1a), a seven-transmembrane G-protein-coupled receptor expressed on anterior pituitary somatotrophs and in the hypothalamic arcuate nucleus. GHS-R1a is the same receptor targeted by endogenous ghrelin. When ipamorelin occupies the receptor, it triggers Gq-mediated activation of phospholipase C, release of IP3, and a rise in intracellular calcium inside somatotrophs. The calcium signal drives exocytosis of pre-stored GH granules into the hypophyseal portal circulation (Raun et al., 1998; Smith et al., 1999).
Two features distinguish this mechanism from continuous exogenous GH administration. First, ipamorelin acts on the pituitary, not on peripheral tissues, so it leverages the animal’s own GH reserve rather than bypassing it. Second, the release is pulsatile. Endogenous GH secretion in healthy mammals occurs in 5 to 7 discrete bursts per 24 hours, with the largest burst during slow-wave sleep. Ipamorelin adds to that architecture rather than flattening it, which is one of the reasons it is a useful probe for studying pulsatile GH physiology in research animals.
Why pulsatile matters
Pulsatility is not a marketing word. Preclinical work has shown that different downstream GH signaling pathways in the liver respond differently to pulsatile versus continuous GH exposure. STAT5b activation, IGF-1 transcription, and sex-specific hepatic gene expression all track the shape of the GH curve, not just the area under it. Researchers studying GH biology therefore often prefer a pulsatile secretagogue like ipamorelin to direct rhGH infusion when the goal is to model physiological GH rather than supraphysiological exposure (Jaffe et al., 1998).
GHRH-independent pathway
Ipamorelin does not act through the GHRH receptor. That is mechanistically important because GHRH and GHS-R1a converge on the same pool of somatotrophs but through separate signaling cascades. In preclinical work, co-administration of a GHRH analog with a GHRP produces a GH response that is larger than the arithmetic sum of either agent alone, a phenomenon documented by Bowers and colleagues across multiple species. This is the pharmacological rationale for the ipamorelin plus CJC-1295 stack discussed later.
Receptor selectivity: why GHS-R1a matters
The ghrelin receptor family is more complicated than a single target. There are at least three molecular entities relevant to GHRP pharmacology:
- GHS-R1a is the functional, G-protein-coupled ghrelin receptor responsible for GH release, appetite signaling, and several central effects. This is the intended target for ipamorelin.
- GHS-R1b is a truncated splice variant with five transmembrane domains that does not couple to G-proteins in the canonical way. Its physiological role remains debated.
- CD36 is a scavenger receptor that binds hexarelin and some other GHRPs in cardiac tissue. CD36 interaction has been linked to non-GH cardiovascular effects of hexarelin in rodent models.
The selling point of ipamorelin in the research literature is that it is highly selective for GHS-R1a. Published binding studies show ipamorelin does not meaningfully engage CD36 and does not activate the neuroendocrine pathways that drive cortisol, ACTH, or prolactin release (Raun et al., 1998). That clean selectivity profile is why ipamorelin is often chosen over hexarelin or GHRP-6 when the research question is specifically about GH and not about the full spectrum of ghrelin receptor biology. For a direct comparison with the less selective cousin in the class, see our hexarelin research guide.
Ipamorelin pharmacology profile vs other GHRPs
The table below compares ipamorelin to the three other commonly referenced GHRPs in the research literature. All values are drawn from preclinical publications.
| Compound | GHS-R1a Selectivity | GH Pulse Shape | Cortisol / ACTH | Prolactin | Plasma Half-Life |
|---|---|---|---|---|---|
| Ipamorelin | High, clean | Pulsatile, pituitary-dependent | No significant elevation | No significant elevation | Approximately 2 hours |
| GHRP-2 | High for GHS-R1a, but broader activity | Pulsatile, larger peak | Mild to moderate elevation | Mild elevation | Approximately 15 to 20 minutes |
| GHRP-6 | Moderate, binds CD36 | Pulsatile, large peak | Measurable elevation | Measurable elevation | Approximately 15 to 30 minutes |
| Hexarelin | Strong GHS-R1a and CD36 | Pulsatile, largest peak | Significant elevation | Significant elevation | Approximately 55 minutes |
Half-life numbers reference plasma residency, not duration of GH pulse. In practical terms, a single ipamorelin injection produces a measurable GH spike that peaks at 15 to 30 minutes post-administration and returns to baseline by roughly 120 minutes. The GH pulse is shorter than the plasma half-life because the pituitary releases its pre-formed GH stores early and needs time to resynthesize granules.
Ipamorelin plus CJC-1295: GHRH and GHRP synergy
The most discussed ipamorelin research question is whether to combine it with a GHRH analog, and if so, with which one. The pharmacological case rests on separate receptor populations converging on the same secretory output. A GHRH analog such as CJC-1295 (with or without DAC) raises cyclic AMP in somatotrophs, priming them for secretion. A GHRP such as ipamorelin then triggers calcium-mediated exocytosis of the primed granules. The combined signal produces a GH release larger than either agent alone.
Two flavors of CJC-1295 are used in research. Modified GRF(1-29), sometimes called CJC-1295 without DAC, has a short half-life of around 30 minutes and is typically co-injected with ipamorelin. CJC-1295 DAC carries a drug affinity complex that extends plasma half-life to roughly 6 to 8 days by reversibly binding albumin, which creates a sustained GHRH tone in the background. Researchers studying discrete GH pulses often prefer modified GRF(1-29) for cleaner time resolution, while those studying chronic GH elevation use CJC-1295 DAC. See our CJC-1295 DAC research guide for the full pharmacology breakdown.
Published reports of additive to synergistic GH release with combined GHRH plus GHRP exposure predate ipamorelin specifically and originate from Bowers’ work with earlier GHRPs in the 1990s. Later studies replicated the pattern with ipamorelin and CJC-1295 in rodent and primate models. The practical upshot for a laboratory is that the combination allows a researcher to probe both arms of GH regulation in a single experiment.
For labs that prefer ready-to-use formats, CertaPeptides stocks a pre-mixed pen format for research which removes the reconstitution step.
Preclinical study summary
The table below summarizes three commonly cited ipamorelin studies. All are preclinical or healthy-volunteer work. None support therapeutic claims.
| Study | Model | Key finding | Identifier |
|---|---|---|---|
| Raun et al., 1998 | In vitro rat pituitary and in vivo swine, rat | First description of ipamorelin as a selective GH secretagogue. Demonstrated GH release without ACTH, cortisol, or prolactin elevation. | PMID 9849822 |
| Gobburu et al., 1999 | Healthy human volunteers, pharmacokinetic study | Characterized ipamorelin plasma kinetics and dose-response for GH release. Reported plasma half-life around 2 hours with dose-proportional exposure. | PMID 10027489 |
| Beck et al., 2014 | Postoperative ileus, rat model | Investigated ipamorelin effect on gastrointestinal motility in a rodent postoperative model, exploring ghrelin-receptor-mediated prokinetic signaling. | PMID 24448593 |
Anderson et al. (2001) extended the early work into swine, showing repeated-dose ipamorelin administration supported GH secretion and body composition shifts in a livestock growth model (PMID 11322503). Nass et al. (2008) studied an oral ghrelin mimetic in older adults, providing reference context for ghrelin-receptor pharmacology in humans though the compound used was not ipamorelin itself (PMID 18981485). Ghigo et al. (1997) is the standard review on the GHRP class as a whole (PMID 9186261).
Pharmacokinetics: absorption, distribution, half-life
Ipamorelin is administered subcutaneously or intramuscularly in preclinical studies. Oral bioavailability is poor because the peptide is degraded by gastrointestinal proteases. After subcutaneous injection in humans, plasma concentration peaks within 15 to 30 minutes. Plasma half-life is approximately 2 hours, which is long for a GHRP (GHRP-6 and hexarelin are shorter) but short compared with GHRH analogs carrying drug affinity complexes.
The GH response does not track plasma ipamorelin linearly. Once the GH pulse is released, somatotrophs enter a refractory window. Additional ipamorelin administered within the next two hours produces a smaller GH response than a fresh injection would. This refractoriness is why research protocols space ipamorelin injections at least two to three hours apart rather than stacking them more densely.
Ipamorelin in study protocols
The following protocol ranges are drawn from the preclinical literature. They describe study design, not user dosing, and are provided for research context only. For research purposes only. Not for human consumption.
- Typical study doses. Preclinical animal protocols commonly use 100 to 300 micrograms per subject per administration when studying acute GH release.
- Administration route. Subcutaneous injection is the default; intramuscular is used in some protocols. Oral and intranasal administration have poor bioavailability and are not standard.
- Frequency. Pulsatile protocols typically space administrations by two to three hours or longer to avoid somatotroph refractoriness. Single-dose pharmacokinetic studies use one administration.
- Protocol length. Acute GH release studies last hours; metabolic or body-composition endpoint studies in animal models run eight to twelve weeks.
- Combination design. When studying GHRH plus GHRP synergy, ipamorelin is co-administered with modified GRF(1-29) or CJC-1295 DAC, typically at matched microgram doses.
Whether to cycle a GH secretagogue in a repeated-dose study depends on the research question and the desired endpoint. See our guide on whether to cycle ipamorelin for the full cycling framework and a look at how researchers structure on-off periods for GH peptides.
Storage and reconstitution for research
Ipamorelin is supplied as a lyophilized powder in sealed glass vials. Handled correctly, the dry peptide is stable for two to three years at refrigerated temperatures. Handled poorly, it loses potency within weeks.
- Lyophilized storage. Store sealed vials at 2 to 8 degrees Celsius, protected from light and moisture. Freezer storage at minus 20 degrees is acceptable for long-term stock and extends stability.
- Reconstitution solvent. Bacteriostatic water for injection is the standard reconstitution solvent in research settings because the benzyl alcohol content suppresses microbial growth across multi-use protocols.
- Reconstituted stability. Once reconstituted, store the solution at 2 to 8 degrees Celsius. Stability in bacteriostatic water is typically two to four weeks, with some preclinical reports extending to eight weeks under tight cold-chain control.
- Handling technique. Inject solvent slowly against the glass wall rather than directly onto the peptide cake. Swirl, do not shake. Avoid repeated temperature cycling.
For a detailed walk-through, see our reconstitution technique guide and peptide storage guide.
Ipamorelin research context in muscle and metabolic studies
Downstream of pulsatile GH release, IGF-1 rises, hepatic lipolytic and anabolic gene programs activate, and nitrogen balance in animal models shifts. These downstream effects are the reason ipamorelin appears in the preclinical literature on sarcopenia, cachexia, postoperative ileus, and bone mineralization. None of this supports a therapeutic or body-composition claim for humans; CertaPeptides sells ipamorelin as a research reagent only. For the broader landscape of GH peptides in muscle research, see our GH peptides in muscle research overview.
Ipamorelin at CertaPeptides
We offer pharmaceutical-grade ipamorelin supplied as a lyophilized powder with a Certificate of Analysis documenting purity (HPLC), identity (mass spec), and microbial testing. Two research vial sizes are available:
- Ipamorelin 5mg research vials for single-study protocols.
- Ipamorelin 10mg research vials for larger or repeated-dose studies.
Both vial sizes are shipped cold-chain within the EU and the UK. All products are supplied for laboratory research use only.
Frequently asked questions
What is ipamorelin’s half-life?
Published pharmacokinetic work reports a plasma half-life of approximately 2 hours after subcutaneous administration. The acute GH pulse is shorter than the plasma half-life because somatotrophs enter a refractory state after releasing their pre-stored GH granules.
Is ipamorelin the safest GHRP?
In preclinical and healthy-volunteer publications, ipamorelin has the cleanest off-target profile of the common GHRPs, with no meaningful elevation of cortisol, ACTH, or prolactin. It is described in the literature as a selective GH secretagogue. CertaPeptides does not make safety claims for human use. All products are supplied for laboratory research purposes only.
How long does ipamorelin take to work in research models?
In animal and early human studies, plasma GH rises within 15 to 30 minutes of a subcutaneous dose and returns to baseline by roughly 120 minutes. Downstream IGF-1 changes unfold over days to weeks of repeated administration.
Does ipamorelin cause hunger like ghrelin?
Ipamorelin binds the same receptor as ghrelin (GHS-R1a) but does not reliably produce the strong appetite signal seen with native ghrelin or with GHRP-6. The precise molecular basis for this selectivity, including possible biased agonism at GHS-R1a, remains an active research area.
Can you stack ipamorelin with CJC-1295?
Yes. The two peptides act on separate receptors (GHRH receptor for CJC-1295, GHS-R1a for ipamorelin) and their co-administration produces an additive to synergistic GH release in preclinical work. This combination is the most common GH peptide stack in the research literature. See our CJC-1295 DAC research guide for the GHRH side of the combination.
Does ipamorelin work without CJC-1295?
Yes. Ipamorelin produces a measurable GH pulse on its own through GHS-R1a activation. Combining it with a GHRH analog amplifies the response but is not required to observe GH release in a research model.
How is ipamorelin different from GHRP-6?
Both act on GHS-R1a, but GHRP-6 also activates neuroendocrine pathways that elevate cortisol and prolactin, and it produces a pronounced appetite signal. Ipamorelin lacks those off-target effects in published work. GHRP-6 has a shorter plasma half-life (roughly 15 to 30 minutes) compared with ipamorelin (roughly 2 hours).
Is ipamorelin a SARM?
No. Selective androgen receptor modulators (SARMs) act on the androgen receptor. Ipamorelin has no androgen receptor activity. It is a ghrelin receptor agonist in the growth hormone-releasing peptide class.
Morning or evening administration in research protocols?
Some preclinical protocols time one ipamorelin administration to align with the nocturnal GH pulse in the research animal, because endogenous GH peaks during slow-wave sleep. The GH response to ipamorelin itself is observed at any time of day. Protocol timing is driven by the research question, not by the compound’s pharmacology.
How does ipamorelin compare with sermorelin or tesamorelin?
Sermorelin and tesamorelin are GHRH analogs acting on the GHRH receptor, not on GHS-R1a. Ipamorelin is a GHRP. They can be combined in research because they act on different receptors. See our sermorelin research guide and tesamorelin research guide for the GHRH side of the comparison.
Compliance and research-use disclaimer
All information in this article describes preclinical and early-phase research on ipamorelin. Nothing here is medical advice, a therapeutic claim, or a recommendation for human use. CertaPeptides supplies ipamorelin and all other research peptides as lyophilized laboratory reagents, labeled for research use only, under Romanian and EU regulatory frameworks. Researchers are responsible for compliance with their institutional ethics board, local chemical handling rules, and any applicable national medicines legislation. For research purposes only. Not for human consumption.
References
- Raun K, Hansen BS, Johansen NL, Thøgersen H, Madsen K, Ankersen M, Andersen PH. (1998). Ipamorelin, the first selective growth hormone secretagogue. European Journal of Endocrinology, 139(5), 552-561. PMID: 9849822.
- Gobburu JV, Agersø H, Jusko WJ, Ynddal L. (1999). Pharmacokinetic-pharmacodynamic modeling of ipamorelin, a growth hormone releasing peptide, in human volunteers. Pharmaceutical Research, 16(9), 1412-1416. PMID: 10496658.
- Beck DE, Sweeney WB, McCarter MD, Ipamorelin 201 and 202 Study Groups. (2014). Prospective, randomized, controlled, proof-of-concept study of the ghrelin mimetic ipamorelin for the management of postoperative ileus in bowel resection patients. International Journal of Colorectal Disease, 29(12), 1527-1534. PMID: 25331030.
- Anderson LL, Jeftinija S, Scanes CG. (2001). Ipamorelin effects on growth hormone secretion and body composition in swine. Endocrine, 14(1), 73-82. PMID: 11322503.
- Nass R, Pezzoli SS, Oliveri MC, Patrie JT, Harrell FE Jr, Clasey JL, et al. (2008). Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults: a randomized trial. Annals of Internal Medicine, 149(9), 601-611. PMID: 18981485.
- Ghigo E, Arvat E, Muccioli G, Camanni F. (1997). Growth hormone-releasing peptides. European Journal of Endocrinology, 136(5), 445-460. PMID: 9186261.
- Smith RG, Van der Ploeg LH, Howard AD, Feighner SD, Cheng K, Hickey GJ, et al. (1997). Peptidomimetic regulation of growth hormone secretion. Endocrine Reviews, 18(5), 621-645. PMID: 9331545.
- Jaffe CA, Ocampo-Lim B, Guo W, Krueger K, Sugahara I, DeMott-Friberg R, Bermann M, Barkan AL. (1998). Regulatory mechanisms of growth hormone secretion are sexually dimorphic. Journal of Clinical Investigation, 102(1), 153-164. PMID: 9649568.
For research purposes only. Not for human consumption.