Ipamorelin – Research Compound Profile

Ipamorelin – Research Compound Profile

Category: Hormonal Research | Molecular Type: Synthetic Pentapeptide (MW: 711.9 Da) | Research Status: Phase II Clinical Data Available

This page compiles published research data for qualified researchers. Ipamorelin is sold exclusively as a research compound, is not approved for human use, and this page does not constitute medical advice. Ipamorelin as characterized in this profile is the unmodified pentapeptide, with no DAC (Drug Affinity Complex) or other half-life-extending moiety added.

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Molecular Overview

Ipamorelin is a synthetic five-amino-acid peptide recognized as the first truly selective growth hormone secretagogue (GHS). Originally developed by Novo Nordisk in the late 1990s, ipamorelin acts as a ghrelin mimetic at the growth hormone secretagogue receptor type 1a (GHS-R1a), producing dose-dependent growth hormone (GH) pulses [1][2]. Its molecular weight is approximately 711.9 Da.

Pharmacokinetic characterization in a Phase I clinical study involving 40 healthy male volunteers demonstrated that ipamorelin exhibits a terminal half-life of approximately 2 hours, a clearance of 0.078 L/h/kg, and a volume of distribution at steady state of 0.22 L/kg [3]. GH peaks were observed at a median of 0.67 hours post-infusion and followed an exponential decline, with the concentration required for half-maximal GH stimulation (SC50) measured at 214 nmol/L — a pharmacodynamic potency constant rather than a human dosing figure [3].

The selectivity profile of ipamorelin — potent GH release without significant elevation of adrenocorticotropic hormone (ACTH), cortisol, or prolactin at the exposures studied — distinguishes it from earlier growth hormone releasing peptides and has made it a compound of considerable interest in endocrine research [1][7].

Structural rationale: Ipamorelin’s pentapeptide sequence (Aib-His-D-2-Nal-D-Phe-Lys-NH₂) is the shortest among the clinically studied GHRPs. The Aib (α-aminoisobutyric acid) residue at position 1 is a quaternary, non-chiral amino acid that sterically blocks aminopeptidase cleavage at the N-terminus, while D-2-naphthylalanine at position 3 occupies a hydrophobic subpocket of GHS-R1a that is believed to underlie the compound’s unusually clean selectivity against the corticotroph and lactotroph signaling pathways engaged by earlier, less selective GHRPs. The C-terminal amide again removes the carboxypeptidase substrate common across the GHRP family.

Mechanism of Action

Ipamorelin exerts its primary pharmacological action by binding to GHS-R1a, the same receptor activated by the endogenous hormone ghrelin [1][9]. Upon binding, ipamorelin triggers intracellular signaling cascades within anterior pituitary somatotroph cells that culminate in the release of stored growth hormone in a pulsatile fashion. The Phase I pharmacokinetic–pharmacodynamic study by Thomsen et al. (1999) demonstrated that ipamorelin infusion across five exposure levels produced dose-proportional plasma concentrations, confirming linear pharmacokinetics within the tested range [3].

What distinguishes ipamorelin from earlier growth hormone releasing peptides such as GHRP-2, GHRP-6, and hexarelin is its remarkable selectivity. The landmark 1998 study by Raun et al. in the European Journal of Endocrinology demonstrated that ipamorelin released GH with a potency and efficacy comparable to GHRP-6 in swine and rat models, yet it did not produce significant changes in plasma ACTH or cortisol levels even at the highest exposure levels tested [1]. GHRP-6 and GHRP-2, by contrast, cause measurable ACTH and cortisol elevations at their GH-effective exposures. This selectivity earned ipamorelin the designation of “the first selective growth hormone secretagogue,” reflecting its unusually clean endocrine profile [1][7].

Beyond GH secretion, ipamorelin exhibits additional physiological activity through GHS-R1a receptors distributed throughout the gastrointestinal tract. Greenwood-Van Meerveld et al. (2012) demonstrated in a rodent model of postoperative ileus that ipamorelin significantly accelerated gastric emptying in a dose-dependent manner relative to vehicle controls [10]. This prokinetic effect occurs via stimulation of cholinergic excitatory neurons within the enteric nervous system, normalizing smooth muscle contractility impaired by surgical manipulation [10]. These preclinical findings contributed to the development of a Phase II clinical program evaluating ipamorelin for postoperative ileus recovery [4].

Published Research Parameters

The following table indexes the study models, durations, and reported observations of selected peer-reviewed publications. Dose, frequency, and administration-route details are deliberately omitted. This is a bibliographic index only — not a protocol and not a recommendation for any use.

Stability & Storage Characteristics

Published data and manufacturer guidelines provide the following stability characteristics for ipamorelin and related synthetic peptides:

• Lyophilized stability: Lyophilized ipamorelin is reported to maintain stability at −20 °C (−4 °F) for extended periods (24+ months). Short-term storage at 2–8 °C (35.6–46.4 °F) is acceptable for weeks to months [14][15].
• Reconstituted solution stability: When reconstituted in bacteriostatic water containing 0.9% benzyl alcohol as a preservative, peptide solutions are generally recommended to be stored at 2–8 °C and utilized within 4 weeks [16]. For extended storage, aliquoting into single-use portions and freezing at −20 °C has been suggested, though repeated freeze–thaw cycles should be avoided.
• Handling considerations: Allowing vials to reach room temperature before opening minimizes condensation that can accelerate peptide degradation [14]. Storage should be upright and away from direct light; amber vials or foil wrapping provide additional photostability.
• General peptide stability: As a small synthetic pentapeptide, ipamorelin is subject to standard peptide degradation pathways including hydrolysis, oxidation, and deamidation, all of which are accelerated by elevated temperature and moisture exposure [14][15]. The tryptophan analog (D-2-Nal) lacks the indole ring of true tryptophan and is consequently more photostable than the Trp-containing GHRPs (GHRP-2, GHRP-6, hexarelin), though the C-terminal amide remains susceptible to slow hydrolytic deamidation over extended storage.

Analytical Characterization

Research-grade ipamorelin is characterized using an orthogonal analytical panel. Reverse-phase HPLC (RP-HPLC) provides the primary purity assessment and resolves hydrolytic and oxidative degradation products from the intact pentapeptide. Electrospray ionization mass spectrometry (ESI-MS) confirms the intact monoisotopic mass. A peptide-content assay (amino acid analysis or quantitative NMR) determines the fraction of lyophilized vial mass attributable to peptide as opposed to residual counter-ion (commonly acetate or trifluoroacetate), water, and buffer salts, since gross vial mass systematically overstates true peptide content. Chiral analysis can additionally confirm that the D-2-Nal and D-Phe centers have not undergone racemization during synthesis. Researchers should retain the quality assurance documentation (CoA) for each lot used, and confirm the absence of any DAC or PEGylation modification if sourcing material intended to represent the unmodified parent peptide.

Key Published Research Findings

All findings below are derived from peer-reviewed publications. Each observation is attributed to its source study.

• Selective GH release without HPA-axis perturbation: In a 1998 European Journal of Endocrinology study, Raun et al. demonstrated that ipamorelin stimulated GH release comparable to GHRP-6 in swine and rat models while producing no statistically significant changes in cortisol, ACTH, or prolactin, even at the highest exposure levels tested [1]. This selectivity profile was corroborated in a 2018 review by Sigalos and Pastuszak in Sexual Medicine Reviews [7].

• Dose-proportional pharmacokinetics in Phase I human trial: In a 1999 Pharmaceutical Research study, Thomsen et al. characterized the pharmacokinetics of ipamorelin in 40 healthy male volunteers across five intravenous exposure levels. Plasma concentrations scaled linearly with exposure, and the terminal half-life was approximately 2 hours, with GH peaks observed at a median of 0.67 hours post-infusion [3].

• Bone mineral content effects in animal models: Svensson et al. (2000) reported in the Journal of Endocrinology that daily ipamorelin treatment in adult female rats significantly increased total body and cortical bone mineral content (BMC) [5]. Separately, Andersen et al. (2001) demonstrated in Growth Hormone & IGF Research that ipamorelin counteracted glucocorticoid-induced decreases in bone formation markers in adult rats, suggesting potential relevance to bone homeostasis research [6].

• Prokinetic effects on gastric motility: In a 2012 Journal of Experimental Pharmacology study, Greenwood-Van Meerveld et al. observed that ipamorelin reversed surgery-induced delayed gastric emptying in a rodent model of postoperative ileus, producing a statistically significant reduction in radiolabeled meal retention relative to vehicle at the lower exposure level studied [10]. Earlier preclinical work by Venkova et al. (2009) in the Journal of Pharmacology and Experimental Therapeutics had similarly documented efficacy in restoring gastric motility following surgical manipulation [17].

• Phase II clinical tolerability data: Beck et al. (2014) published results from a prospective, randomized, controlled Phase II trial in the International Journal of Colorectal Disease involving 114 bowel-resection patients receiving twice-daily IV ipamorelin or placebo. The overall incidence of treatment-emergent adverse events was numerically lower in the ipamorelin arm than in the placebo arm [4].

• Absence of receptor desensitization with chronic administration: Jiménez-Reina et al. (2002) reported in Histology and Histopathology that three-week daily ipamorelin treatment in young female rats did not diminish the magnitude of in vitro GH release from isolated pituitary cells, suggesting that sustained administration may not readily desensitize the GH release mechanism in this model [8].

• Ghrelin receptor context: As reviewed by Kojima and Kangawa (2005) in Physiological Reviews, GHS-R1a — the molecular target of ipamorelin — mediates a broad array of physiological functions beyond GH secretion, including energy homeostasis, appetite regulation, and gastrointestinal motility. Ipamorelin’s activity at this receptor situates it within a growing class of ghrelin-mimetic research tools [9].

Safety Profile in Published Literature

Published preclinical and clinical data provide the following safety observations for ipamorelin:

• Phase II clinical trial (Beck et al., 2014): In the largest published clinical study of ipamorelin, involving 114 patients receiving twice-daily IV doses following bowel resection, the treatment-emergent adverse event rate was numerically lower in the ipamorelin group than the placebo group. The authors noted that the compound was generally well tolerated in this post-surgical population [4].

• Endocrine selectivity: Unlike other GHRPs (GHRP-2, GHRP-6, hexarelin), ipamorelin did not produce significant elevations in ACTH, cortisol, or prolactin at GH-effective exposures in preclinical models, representing a differentiated safety profile among growth hormone secretagogues [1][7].

• Mild appetite stimulation: As a ghrelin receptor agonist, ipamorelin has been noted in the literature to produce modest appetite-stimulating effects, though reviews describe this as considerably less pronounced than with GHRP-6 or non-peptide ghrelin mimetics [7][9].

• Transient fluid retention: Sigalos and Pastuszak (2018) noted in their review of growth hormone secretagogues that mild fluid retention has been reported as a class-associated effect, typically transient in nature [7].

• Toxicological data limitations: Published safety data for ipamorelin are derived primarily from short-duration preclinical studies and a single Phase II clinical trial. Long-term safety data in human populations have not been published in the peer-reviewed literature.

Regulatory Status

• FDA approval status: Ipamorelin has not been approved by the U.S. Food and Drug Administration (FDA) for any therapeutic indication.
• Clinical trial activity: A Phase II multicenter trial (NCT00672074) evaluated ipamorelin for postoperative ileus recovery in bowel-resection patients [18]. No Phase III trials have been registered as of the literature review date.
• Research compound classification: Ipamorelin is sold exclusively as a research compound. It is not intended for human consumption, therapeutic use, or dietary supplementation.
• Regulatory context: Researchers should ensure that all work involving ipamorelin complies with applicable institutional, local, and federal regulations governing the use of research peptides.

References

1. European Journal of Endocrinology (1998) — Raun K, Hansen BS, Johansen NL, et al. Ipamorelin, the first selective growth hormone secretagogue. Eur J Endocrinol. 1998;139(5):552-561. View Source

2. Translational Andrology and Urology (2020) — Sinha DK, Balasubramanian A, Tatem AJ, et al. Beyond the androgen receptor: the role of growth hormone secretagogues in the modern management of body composition in hypogonadal males. Transl Androl Urol. 2020;9(Suppl 2):S149-S159. View Source

3. Pharmaceutical Research (1999) — Thomsen JB, Moesgaard B, Kulkarni A, et al. Pharmacokinetic-pharmacodynamic modeling of ipamorelin, a growth hormone releasing peptide, in human volunteers. Pharm Res. 1999;16(9):1412-1416. View Source

4. International Journal of Colorectal Disease (2014) — Beck DE, Sweeney WB, McCarter MD, et al. Prospective, randomized, controlled, proof-of-concept study of the ghrelin mimetic ipamorelin for the management of postoperative ileus in bowel resection patients. Int J Colorectal Dis. 2014;29(12):1527-1534. View Source

5. Journal of Endocrinology (2000) — Svensson J, Lall S, Dickson SL, et al. The GH secretagogues ipamorelin and GH-releasing peptide-6 increase bone mineral content in adult female rats. J Endocrinol. 2000;165(3):569-577. View Source

6. Growth Hormone & IGF Research (2001) — Andersen NB, Malmlöf K, Johansen PB, et al. The growth hormone secretagogue ipamorelin counteracts glucocorticoid-induced decrease in bone formation of adult rats. Growth Horm IGF Res. 2001;11(5):266-272. View Source

7. Sexual Medicine Reviews (2018) — Sigalos JT, Pastuszak AW. The Safety and Efficacy of Growth Hormone Secretagogues. Sex Med Rev. 2018;6(1):45-53. View Source

8. Histology and Histopathology (2002) — Jiménez-Reina L, Cañete R, de la Torre MJ, Bernal G. Influence of chronic treatment with the growth hormone secretagogue ipamorelin, in young female rats: somatotroph response in vitro. Histol Histopathol. 2002;17(3):707-714. View Source

9. Physiological Reviews (2005) — Kojima M, Kangawa K. Ghrelin: structure and function. Physiol Rev. 2005;85(2):495-522. View Source

10. Journal of Experimental Pharmacology (2012) — Greenwood-Van Meerveld B, Tyler K, Mohammadi E, Pietra C. Efficacy of ipamorelin, a ghrelin mimetic, on gastric dysmotility in a rodent model of postoperative ileus. J Exp Pharmacol. 2012;4:149-155. View Source

14. Bachem Peptide Manufacturer — Handling and Storage Guidelines for Peptides. Technical best-practices document on peptide lyophilization and storage stability. View Source

15. NIBSC (National Institute for Biological Standards and Control) — Peptide Handling, Dissolution & Storage Guidelines. View Source

16. Creative Peptides — How Long Do Peptides Last? Peptide Stability & Shelf Life. Technical article on reconstituted peptide stability and bacteriostatic water considerations. View Source

17. Journal of Pharmacology and Experimental Therapeutics (2009) — Venkova K, Mann W, Nelson R, Greenwood-Van Meerveld B. Efficacy of ipamorelin, a novel ghrelin mimetic, in a rodent model of postoperative ileus. J Pharmacol Exp Ther. 2009;329(3):1110-1116. View Source

18. ClinicalTrials.gov (NCT00672074) — Safety and Efficacy of Ipamorelin for the Treatment of Postoperative Ileus. Phase II multicenter trial, Helsinn Therapeutics. View Source

⚠️ Disclaimer: This page is provided for educational and informational purposes only and does not constitute medical advice, diagnosis, or treatment recommendations. Ipamorelin is sold exclusively as a research compound and has not been approved by the FDA for human consumption. It is not intended for human use or self-administration. All information is derived from published peer-reviewed literature. Research must comply with all applicable laws, regulations, and institutional guidelines.

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