GHRP-6 – Research Compound Profile

GHRP-6 – Research Compound Profile

Category: Hormonal Research | Molecular Type: Synthetic Hexapeptide (His-DTrp-Ala-Trp-DPhe-Lys-NH₂) | Research Status: Phase I Human Safety Trial Completed

This page compiles published research data for qualified researchers. GHRP-6 is not approved for human use, is sold exclusively as a research compound, is not intended for human consumption or self-administration, and this page does not constitute medical advice.

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Molecular Overview

GHRP-6 (Growth Hormone-Releasing Peptide 6) is a synthetic hexapeptide growth hormone secretagogue first described by Bowers et al. in 1984 [1]. Its amino acid sequence — His-DTrp-Ala-Trp-DPhe-Lys-NH₂ — incorporates two D-amino acids (D-Trp and D-Phe) that confer resistance to enzymatic degradation and enable receptor binding to the growth hormone secretagogue receptor type 1a (GHS-R1a) [1][2].

GHRP-6 is one of the most extensively studied members of the growth hormone-releasing peptide family, with pharmacokinetic characterization documenting a plasma elimination half-life of approximately 2.5 ± 1.1 hours and a rapid distribution half-life of 7.6 ± 1.9 minutes following intravenous administration in healthy male volunteers [5]. Unlike many GH secretagogues, GHRP-6 possesses dual-receptor pharmacology — binding both GHS-R1a for endocrine effects and CD36 (fatty acid translocase) for tissue-protective activity — a characteristic that has driven extensive investigation into its cytoprotective properties across multiple organ systems [2][18].

Phase I dose-escalation safety data have been published for GHRP-6 in healthy human volunteers [3], and the compound has been evaluated in preclinical and translational research settings spanning endocrine physiology, cardiology, hepatology, and wound healing [2].

Structural rationale: The His at position 1 is essential for GHS-R1a engagement, forming a key hydrogen-bonding contact within the receptor’s orthosteric pocket. D-Trp at position 2 and D-Phe at position 5 are the two non-proteinogenic substitutions that distinguish GHRP-6 from a hypothetical all-L-amino-acid analog; both confer resistance to trypsin- and chymotrypsin-like proteases that would otherwise cleave the native peptide bond geometry within minutes. The C-terminal lysinamide (Lys-NH₂) removes the free carboxylate recognized by carboxypeptidases, further extending circulating half-life relative to an unmodified linear hexapeptide. This constellation of modifications — shared in modified form across the entire GHRP class — is the structural basis for GHRP-6’s markedly greater metabolic stability compared with unmodified growth-hormone-releasing fragments.

Mechanism of Action

GHRP-6 exerts its primary endocrine effects by binding to the growth hormone secretagogue receptor type 1a (GHS-R1a), a seven-transmembrane G protein-coupled receptor expressed on somatotroph cells of the anterior pituitary and on hypothalamic neurons [1][2]. Unlike growth hormone-releasing hormone (GHRH), which activates the protein kinase A pathway via the GHRH receptor, GHRP-6 signals through a distinct mechanism involving Gq/i-coupled phospholipase C activation [6]. This triggers an acute, pulsatile burst of GH release from somatotroph cells while simultaneously suppressing somatostatin — the hypothalamic inhibitory signal that ordinarily dampens GH secretion [2][17].

Critically, the GH pulses generated by GHRP-6 remain subject to normal physiological negative feedback via IGF-1 and somatostatin, a mechanism the literature associates with reduced likelihood of the supraphysiological GH elevations sometimes observed with exogenous GH administration [6][12]. When GHRP-6 is co-administered with a GHRH analog in research protocols, the two peptides act synergistically — GHRP-6 reduces somatostatin tone while GHRH provides a direct pituitary stimulus — resulting in GH peaks substantially greater than either agent alone, as documented by Bowers (1998) and Leal-Cerro et al. (1995) [6][10].

Beyond the GH axis, GHRP-6 binds a second receptor — CD36 (also known as fatty acid translocase) — a class B scavenger receptor expressed on cardiomyocytes, monocytes/macrophages, endothelial cells, and multiple organ parenchyma [2][18]. Bodart et al. (2002) demonstrated that CD36 mediates the cardiovascular action of growth hormone-releasing peptides in the heart [18]. CD36 activation by GHRP-6 engages prosurvival intracellular cascades, most notably the PI3K/AKT1 pathway and the induction of hypoxia-inducible factor-1α (HIF-1α), which promote cellular survival under ischemic or oxidative stress conditions [4][19]. This dual-receptor pharmacology — GHS-R1a for endocrine effects and CD36 for cytoprotection — sets GHRP-6 apart from the endogenous ligand ghrelin and from GHRH analogs, neither of which possesses equivalent tissue-protective activity [2].

GHRP-6 also displays anti-fibrotic properties, acting via upregulation of PPARγ (peroxisome proliferator-activated receptor gamma) to suppress TGF-β1 and connective tissue growth factor (CTGF) expression, as documented in models of liver fibrosis and hypertrophic scarring [2][21][22].

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 on GHRP-6 stability report the following characteristics relevant to research handling:

• Lyophilized form: Lyophilized GHRP-6 is reported to be stable for 24+ months when stored at −20 °C (−4 °F) in a dry, dark environment. Desiccant protection against moisture exposure is recommended in the literature [8].
• Reconstituted solution: Published storage recommendations indicate refrigeration at 2–8 °C (35.6–46.4 °F), protected from direct light, with reported stability of approximately 4 weeks under these conditions [8].
• Freeze-thaw sensitivity: Repeated freeze-thaw cycles are documented to compromise peptide integrity. Published protocols indicate that aliquoting reconstituted solution into separate sterile containers reduces degradation from repeated access [8].
• Temperature equilibration: Laboratory protocols note that allowing refrigerated peptide solutions to equilibrate to room temperature for several minutes before use minimizes condensation-related contamination.
• Degradation chemistry: As with other Trp-containing GHRPs, the two tryptophan-derived indole rings are the primary sites of oxidative degradation under prolonged light exposure, while the C-terminal amide is subject to slow hydrolytic deamidation over extended storage in aqueous solution. Both pathways are readily distinguished from the parent peptide by mass shift on LC-MS [8].

Analytical Characterization

Research-grade GHRP-6 is characterized using an orthogonal analytical panel. Reverse-phase HPLC (RP-HPLC) provides the primary purity assessment and resolves oxidative and hydrolytic degradation products from the intact hexapeptide. Electrospray ionization mass spectrometry (ESI-MS) confirms the intact monoisotopic mass, distinguishing the parent amide from deamidated or oxidized (Trp → oxindolylalanine or kynurenine, +16 Da) impurities. A peptide-content assay (amino acid analysis or quantitative NMR) determines the fraction of lyophilized mass attributable to peptide as opposed to residual counter-ion, water, and buffer salts, since gross vial mass systematically overstates peptide content. Chiral analysis can additionally confirm that the D-Trp and D-Phe centers have not undergone racemization during synthesis. Researchers should retain the quality assurance documentation (CoA) for each lot used.

Key Published Research Findings

Growth Hormone Release

In a 1993 Journal of Clinical Endocrinology and Metabolism study, Cordido et al. demonstrated that combined intravenous administration of GHRP-6 with GHRH produced a substantial GH discharge in obese subjects — a population in which GH secretion is typically blunted [9]. Bowers (1998) comprehensively reviewed GHRP-6 dose-response characteristics and documented the synergistic interaction with GHRH, reporting GH peaks substantially greater than either agent administered alone [6]. Leal-Cerro et al. (1995) further confirmed this synergistic GH response in adults with GH deficiency [10]. Bellone et al. (1995) demonstrated a GH-releasing effect following oral administration of GHRP-6 in children with short stature, indicating oral bioavailability [13].

Cardioprotection

In a 2007 Clinical Science study using a porcine model of acute myocardial infarction, Berlanga et al. reported that GHRP-6 administration reduced infarct size relative to the area at risk, enhanced BCL-2 survival signaling, decreased reactive oxygen species (ROS) generation, and preserved antioxidant defenses [4]. Berlanga-Acosta et al. (2017) reviewed evidence that GHRP-6 substantially attenuated ejection fraction decline in doxorubicin-induced cardiomyopathy models [2]. In a 2003 Journal of Pharmacology and Experimental Therapeutics study, Shen et al. demonstrated that pretreatment with a growth hormone secretagogue (GHRP-6 analog) in a canine model of dilated cardiomyopathy followed by acute infarction markedly improved survival relative to vehicle-treated and GH-treated control groups, with this cardioprotective effect operating independently of the growth hormone pathway [20]. Valiente-Mustelier et al. (2013) documented an elevation in ejection fraction during in vivo echocardiographic characterization of GHRP-6’s cardiotropic effects [16].

Appetite and Orexigenic Effects

GHRP-6 is documented as the strongest appetite stimulant among the GHRP family due to its potent activation of GHS-R1a, the native ghrelin receptor, as reviewed by Sigalos and Pastuszak (2018) [12]. Berlanga-Acosta et al. (2017) noted that this orexigenic property distinguishes GHRP-6 from GHRP-2 and Ipamorelin, which demonstrate milder appetite-stimulating effects [2]. Laferrere et al. (2006) studied the structurally related GHRP-2 in obese subjects and reported a substantial increase in food intake at the higher exposure level, supporting the appetite-stimulatory class effect of GHS-R1a agonists [23].

Anti-Fibrotic Effects

In a 2012 study, Berlanga-Acosta et al. reported that GHRP-6 reduced liver fibrosis in CCl₄-chronically intoxicated rats via PPARγ-mediated suppression of TGF-β1 and connective tissue growth factor (CTGF) expression [21]. Mendoza-Marí et al. (2016) demonstrated in a wound healing model that GHRP-6 enhanced the healing process and improved the esthetic outcome of wounds, with reduced hypertrophic scarring and collagen deposition [22].

Multi-Organ Cytoprotection

In a 2006 Clinical Science study, Cibrian et al. demonstrated that in a hepatic ischemia-reperfusion model, GHRP-6 attenuated damage to the liver, lungs, kidneys, and small intestine simultaneously, demonstrating systemic protective effects mediated through PI3K/AKT1 and HIF-1α prosurvival signaling pathways [19]. Bodart et al. (2002) established that the CD36 receptor mediates these cardiovascular and tissue-protective actions of growth hormone-releasing peptides in the heart [18].

Sleep Architecture

In a 1995 Neuroendocrinology study, Frieboes et al. administered intravenous GHRP-6 boluses during sleep in healthy young males and observed increased serum GH and increased mean time spent in stage 2 sleep without disruption of slow-wave sleep patterns [14].

Safety Profile in Published Literature

Phase I Human Data

Selman-Housein-Bernal et al. (2014) conducted a Phase I dose-escalation clinical trial of GHRP-6 in healthy human volunteers receiving intravenous doses. No serious adverse events were reported [3]. Berlanga-Acosta et al. (2017) reviewed the cumulative safety evidence and confirmed a broad safety profile across published studies [2].

Documented Adverse Observations

• Appetite stimulation: The most consistently reported effect across studies. GHRP-6’s ghrelin-mimicking properties produce significant appetite increase, distinguishing it from GHRP-2 and Ipamorelin, which demonstrate weaker orexigenic effects [12][23].
• Transient cortisol and ACTH elevation: Frieboes et al. (1995) and Sigalos & Pastuszak (2018) documented mild, transient increases in cortisol and ACTH, particularly with intravenous administration. These elevations were generally not considered clinically significant and normalized rapidly [14][12].
• Drug interactions: Published data indicated no significant interaction between GHRP-6 and the beta-blocker metoprolol in a pharmacological interaction study [3][16].
• Nutrient-status sensitivity: A 1997 European Journal of Endocrinology study documented that elevated blood glucose and free fatty acid levels blunted the GH response to GHRPs, indicating metabolic state as a significant variable in research protocols [7].

Toxicology Limitations

The majority of published safety data derives from acute or short-term administration studies. Long-term chronic safety data in human subjects remains limited. Animal model studies have employed chronic administration (e.g., 21-day pretreatment in the Shen et al. canine model [20]) without reported serious adverse events, but comprehensive long-term toxicology profiles have not been published.

Regulatory Status

• FDA approval: GHRP-6 is not approved by the FDA for human therapeutic use.
• FDA safety notices: The FDA (2023) has listed GHRP-6 under the 503B category of “Substances in Compounding that May Present Significant Safety Risks,” citing potential immunogenicity concerns for certain routes of administration [24].
• Clinical trial status: Phase I dose-escalation safety data have been published [3]. No currently active Phase II or Phase III trials are widely reported in the literature.
• Research-only status: GHRP-6 is sold exclusively as a research compound. All procurement and use must comply with applicable laws, regulations, and institutional guidelines.

References

1. Endocrinology (1984) — Bowers CY, Momany FA, Reynolds GA, Hong A. On the in vitro and in vivo activity of a new synthetic hexapeptide that acts on the pituitary to specifically release growth hormone. View Source

2. Clinical Medicine Insights: Cardiology (2017) — Berlanga-Acosta J, Abreu-Cruz A, et al. Synthetic Growth Hormone-Releasing Peptides (GHRPs): A Historical Appraisal of the Evidences Supporting Their Cytoprotective Effects. View Source

3. Investigaciones Médico Quirúrgicas (2014) — Selman-Housein-Bernal KH, Hernández-Bernal F, et al. Clinical safety of growth hormone-releasing peptide-6 (GHRP-6) in healthy volunteers (phase I dose-escalation trial). View Source

4. Clinical Science (2007) — Berlanga J, Cibrian D, Guevara L, et al. Growth-hormone-releasing peptide 6 (GHRP6) prevents oxidant cytotoxicity and reduces myocardial necrosis in a model of acute myocardial infarction. View Source

5. European Journal of Pharmaceutical Sciences (2013) — Pharmacokinetic study of Growth Hormone-Releasing Peptide 6 (GHRP-6) in nine male healthy volunteers. Distribution half-life: 7.6 ± 1.9 min; elimination half-life: 2.5 ± 1.1 hours. View Source

6. Cellular and Molecular Life Sciences (1998) — Bowers CY. Growth hormone-releasing peptide (GHRP). Comprehensive review of GHRP pharmacology, synergy with GHRH, and dose-response characteristics. View Source

7. European Journal of Endocrinology (1997) — Growth hormone-releasing peptides: effect of nutrient intake and metabolic status on GH response. View Source

8. Peptides Lab UK (2024) — Understanding GHRP-6 stability and storage for lab applications. Lyophilized storage at −20°C; reconstituted stability at 2–8°C. View Source

9. Journal of Clinical Endocrinology and Metabolism (1993) — Cordido F, Penalva A, Dieguez C, Casanueva FF. Massive growth hormone (GH) discharge in obese subjects after the combined administration of GH-releasing hormone and GHRP-6. View Source

10. Journal of Clinical Endocrinology and Metabolism (1995) — Leal-Cerro A, Garcia E, Astorga R, et al. Growth hormone (GH) responses to the combined administration of GH-releasing hormone plus GH-releasing peptide 6 in adults with GH deficiency. View Source

11. Sexual Medicine Reviews (2018) — Sigalos JT, Pastuszak AW. The Safety and Efficacy of Growth Hormone Secretagogues. Comprehensive review of GHRPs including GHRP-6 safety, dosing, and side effect profiles. View Source

12. Sexual Medicine Reviews (2018) — Sigalos JT, Pastuszak AW. The Safety and Efficacy of Growth Hormone Secretagogues. Comprehensive review of GHRPs including GHRP-6 safety and side effect profiles. View Source

13. European Journal of Endocrinology (1995) — Bellone J, Ghizzoni L, Aimaretti G, et al. Growth hormone-releasing effect of oral growth hormone-releasing peptide 6 (GHRP-6) administration in children with short stature. View Source

14. Neuroendocrinology (1995) — Frieboes RM, Murck H, Maier P, et al. Growth hormone-releasing peptide-6 stimulates sleep, growth hormone, ACTH and cortisol release in normal man. View Source

15. Endocrine Reviews (1997) — Smith RG, Van der Ploeg LHT, et al. Peptidomimetic regulation of growth hormone secretion. View Source

16. Biotecnología Aplicada (2013) — Valiente-Mustelier J, Garcia del Barco D, Guillen-Nieto G, et al. Cardiotropic effect of GHRP-6: in vivo characterization by echocardiography. Reported elevation in ejection fraction. View Source

17. European Journal of Endocrinology (1997) — Arvat E, di Vito L, Maccagno B, et al. Effects of GHRP-2 and hexarelin, two synthetic GH-releasing peptides, on GH, prolactin, ACTH and cortisol levels in man. View Source

18. Circulation Research (2002) — Bodart V, Febbraio M, Demers A, et al. CD36 mediates the cardiovascular action of growth hormone-releasing peptides in the heart. View Source

19. Clinical Science (2006) — Cibrian D, Ajamieh H, Berlanga J, et al. Use of growth-hormone-releasing peptide-6 (GHRP-6) for the prevention of multiple organ failure. Demonstrated systemic cytoprotection via PI3K/AKT1 and HIF-1α pathways. View Source

20. Journal of Pharmacology and Experimental Therapeutics (2003) — Shen YT, Lynch JJ, Hargreaves RJ, Gould RJ. A growth hormone secretagogue prevents ischemic-induced mortality independently of the growth hormone pathway in dogs with chronic dilated cardiomyopathy. View Source

21. Biotecnología Aplicada (2012) — Berlanga-Acosta J, Vázquez-Blomquist D, et al. Growth Hormone Releasing Peptide 6 (GHRP6) reduces liver fibrosis in CCl4 chronically intoxicated rats. View Source

22. Plastic Surgery International (2016) — Mendoza-Marí Y, Fernández-Mayola M, et al. Growth hormone-releasing peptide 6 enhances the healing process and improves the esthetic outcome of the wounds. View Source

23. Obesity (2006) — Laferrere B, Hart AB, Bowers CY. Obese subjects respond to the stimulatory effect of the ghrelin agonist growth hormone-releasing peptide-2 on food intake. GHRP-2 (structurally related to GHRP-6) increased food intake at the higher exposure level tested. View Source

24. FDA (2023) — Substances in Compounding that May Present Significant Safety Risks. GHRP-6 listed under 503B category with potential immunogenicity concerns for certain routes. View Source

⚠️ Disclaimer: This page is provided for educational and informational purposes only and does not constitute medical advice, diagnosis, or treatment recommendations. GHRP-6 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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