A potent synthetic hexapeptide GHRP with strong GH-releasing activity and additional cardioprotective properties mediated through the CD36 receptor.
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Buy Now →Hexarelin is a synthetic hexapeptide (His-D-2-MeTrp-Ala-Trp-D-Phe-Lys-NH2) developed in the late 1980s and early 1990s as part of a systematic effort to create orally or parenterally active growth hormone-releasing peptides (GHRPs). It belongs to the same peptide family as GHRP-2 and GHRP-6 but stands apart within that family for two distinctive properties: it produces the most potent acute growth hormone secretory response of any synthetic GHRP studied to date, and it binds with high affinity to CD36 — a scavenger receptor expressed on cardiomyocytes and other tissues — producing GH-independent cardiovascular effects that have driven a substantial and largely separate body of cardiac research.
The name hexarelin reflects its six-amino-acid structure. The D-amino acid substitutions at positions 2 and 5 (D-2-methyltryptophan and D-phenylalanine) are critical for protease resistance and receptor binding affinity — modifications that distinguish it pharmacologically from the endogenous GH secretagogue ghrelin, which Hexarelin predates as a synthetic tool. When ghrelin’s receptor (the growth hormone secretagogue receptor type 1a, GHS-R1a) was identified and deorphanized in 1999, it was partly through the use of Hexarelin and related synthetic GHRPs that had been employed as research tools for over a decade.
Hexarelin’s cardiac pharmacology emerged somewhat serendipitously. Researchers noted that Hexarelin produced cardiovascular effects — particularly improvements in cardiac output and reductions in left ventricular afterload — that were disproportionate to its GH-releasing activity and persisted in GH-deficient animals where no GH response was possible. This observation led to the identification of CD36 as a cardiac Hexarelin receptor that mediates direct myocardial and vascular effects independently of the pituitary GHS-R1a axis. The compound thus straddles two distinct research domains: endocrinological research into GH/IGF-1 axis modulation, and cardiovascular research into myocardial protection, cardiac remodeling, and ischemic injury.
An important practical consideration for Hexarelin research is tolerance development. Unlike GHRP-6 or Ipamorelin, Hexarelin’s GH-releasing effects show relatively rapid desensitization with continuous administration — GH responses diminish by 50–70% within 2–4 weeks of twice-daily dosing in human studies. This is thought to result from both GHS-R1a downregulation at the pituitary and an increase in hypothalamic somatostatin tone. Intermittent dosing strategies or on/off cycling are therefore important design considerations for longer-duration research protocols.
Explore Hexarelin side-by-side with other GHRPs in the Peptide Database, or use the dosage calculators to plan your research schedule.
Hexarelin’s primary endocrine mechanism is activation of the growth hormone secretagogue receptor type 1a (GHS-R1a), a seven-transmembrane G protein-coupled receptor expressed at high density on somatotroph cells in the anterior pituitary and at lower but functionally significant levels in the arcuate nucleus of the hypothalamus. GHS-R1a couples primarily to Gαq/11, triggering phospholipase C activation, IP3-mediated calcium release from the endoplasmic reticulum, and protein kinase C activation. The resulting calcium transient triggers exocytosis of GH-containing secretory granules from pituitary somatotrophs — the same cells that respond to endogenous GHRH. Hexarelin’s GH-releasing potency at GHS-R1a exceeds that of GHRP-2 and GHRP-6 due to its higher binding affinity (Ki approximately 0.1 nM) and the D-amino acid modifications that slow metabolic clearance. At the hypothalamic level, Hexarelin simultaneously stimulates GHRH release (amplifying pituitary stimulation) and, through a separate mechanism, suppresses somatostatin secretion — two complementary actions that explain why GHRPs produce larger GH bursts than GHRH alone. The combination of direct pituitary stimulation, enhanced GHRH drive, and reduced somatostatin inhibition makes Hexarelin a highly effective but complex neuroendocrine tool.
The cardioprotective pharmacology of Hexarelin operates through a completely separate receptor system. CD36, also known as fatty acid translocase, is a class B scavenger receptor and multi-ligand transporter expressed on the surface of cardiomyocytes, endothelial cells, vascular smooth muscle cells, macrophages, and platelets. Its canonical function involves binding and internalization of long-chain fatty acids, oxidized LDL, and thrombospondin, making it a nexus for cardiac lipid metabolism and atherogenic signaling. Hexarelin binds CD36 with nanomolar affinity, activating intracellular signaling cascades that include Src-family kinase activation, PI3K/Akt phosphorylation, and downstream activation of the nuclear receptor PPARγ (peroxisome proliferator-activated receptor gamma). PPARγ is a lipid-sensing transcription factor whose activation in cardiac tissue drives a gene expression program favoring mitochondrial fatty acid oxidation efficiency, anti-inflammatory cytokine profiles, and reduced cardiac fibrosis (through suppression of TGF-β target genes). The net result is a cardioprotective phenotype — reduced ischemic injury, attenuated adverse remodeling, and improved metabolic efficiency — that operates independently of any pituitary or GH-related mechanism.
A third mechanistic dimension of Hexarelin’s cardiac activity involves mitochondrial CD36. The heart is an obligate aerobic organ that derives approximately 70% of its ATP from mitochondrial beta-oxidation of long-chain fatty acids; the remainder comes from glucose oxidation. CD36 is expressed not only on the cardiomyocyte plasma membrane but also on the outer mitochondrial membrane, where it facilitates the transfer of activated fatty acids to the beta-oxidation machinery. Hexarelin’s engagement of mitochondrial CD36 appears to enhance the efficiency of this fatty acid import step, potentially increasing ATP production per unit substrate — a metabolic advantage that is particularly relevant in heart failure, where mitochondrial function is impaired and the heart tends to shift toward less efficient glucose-dependent metabolism while losing fatty acid oxidative capacity. By activating PPARγ (which transcriptionally upregulates beta-oxidation enzyme genes) while simultaneously facilitating fatty acid import through CD36, Hexarelin may act at multiple points in the cardiac fatty acid utilization pathway. Whether this metabolic enhancement translates to clinically meaningful improvements in cardiac efficiency is an active area of investigation in heart failure and diabetic cardiomyopathy animal models.
Cardiac fibrosis — the replacement of functional myocardium with collagen-rich scar tissue — is a central pathological mechanism in heart failure progression, ventricular hypertrophy, and diastolic dysfunction. It reduces cardiac compliance, impairs electrical conduction, and ultimately diminishes systolic function. Several animal model studies have demonstrated that Hexarelin treatment reduces the degree of cardiac fibrosis in hearts subjected to myocardial infarction, pressure overload, or doxorubicin-induced cardiotoxicity. Mechanistically, these anti-fibrotic effects appear to involve PPARγ-mediated suppression of TGF-β target genes in cardiac fibroblasts and macrophages — reducing myofibroblast differentiation and collagen deposition. Macrophage CD36 engagement by Hexarelin shifts macrophage polarization from a pro-fibrotic (M2-like) phenotype toward a resolution phenotype, further reducing fibrogenic cytokine output in the injured myocardium. Notably, these anti-fibrotic effects have been demonstrated in studies using GH-deficient hypophysectomized rats, confirming that they are mediated through CD36 rather than through GH/IGF-1 axis activation. The magnitude of fibrosis reduction in these models is substantial — histological studies report 30–50% reductions in collagen content in Hexarelin-treated versus vehicle-treated infarcted hearts — making this one of the most compelling aspects of the compound’s cardiac research profile.
Post-myocardial infarction cardiac remodeling involves a progressive deterioration of left ventricular geometry and function that begins with infarct expansion and wall thinning, proceeds through eccentric hypertrophy of non-infarcted myocardium, and ultimately results in a dilated, poorly functioning ventricle. Hexarelin treatment in rodent MI models has been shown to preserve left ventricular ejection fraction, reduce end-systolic and end-diastolic volumes, and attenuate wall motion abnormalities compared to saline controls when administered in the peri-infarction period. Echocardiographic studies following acute coronary ligation in rats demonstrate significantly better preserved fractional shortening (a surrogate for global systolic function) at 4 weeks in Hexarelin-treated animals. Importantly, the preservation of LV function appears to involve not only the acute anti-apoptotic effects of Hexarelin on cardiomyocytes in the peri-infarct border zone (reducing infarct expansion through Akt-mediated cell survival signaling) but also the chronic anti-fibrotic effects described above that prevent progressive remodeling over weeks to months. The combination of acute cellular protection and chronic structural preservation makes Hexarelin a potentially multi-mechanistic cardioprotective tool for research in acute coronary syndrome models.
Hexarelin’s vascular effects are distinct from its cardiomyocyte effects and involve a combination of endothelium-dependent and endothelium-independent mechanisms. In isolated perfused heart preparations (Langendorff model), Hexarelin increases coronary perfusion pressure-normalized flow, indicating direct coronary vasodilatory activity. This vasodilation appears to be partially nitric oxide-dependent, as it is attenuated by eNOS inhibitors, and partially involves direct smooth muscle effects mediated through CD36 expressed on vascular smooth muscle cells. In animal models of myocardial ischemia, pre-treatment with Hexarelin has been shown to improve coronary collateral flow in the peri-infarct region, potentially reducing ischemic injury extent by maintaining some oxygen delivery to at-risk myocardium. GHS-R1a is also expressed in vascular endothelium, and endothelial GHS-R1a activation by Hexarelin may contribute to NO-dependent vasodilation through eNOS phosphorylation downstream of PI3K/Akt signaling — the same pathway activated by cardioprotective interventions including ischemic preconditioning.
Hexarelin’s growth hormone-releasing effects in humans are among the most comprehensively characterized of any GHRP. Single subcutaneous or IV doses of 1–2 µg/kg body weight produce peak GH concentrations typically 5–10 times baseline within 15–30 minutes, with a return to baseline by 60–90 minutes. This represents a substantially larger GH pulse than equivalent doses of GHRP-2, GHRP-6, or Ipamorelin in most published comparative studies, consistent with Hexarelin’s higher GHS-R1a affinity and its broader hypothalamic effects on GHRH and somatostatin. However, tolerance development is a critical practical limitation of Hexarelin for chronic GH-stimulation research. Studies of twice-daily subcutaneous administration over 2–4 weeks in healthy adults showed progressive attenuation of GH response, with peak GH declining to 30–50% of initial values by day 14. This blunting is thought to involve both receptor desensitization and upregulation of hypothalamic somatostatin tone as a compensatory response to sustained GHS-R1a stimulation. Cycle designs using Hexarelin for limited periods (days to 1–2 weeks) with extended rest intervals, or combination with GHRH analogs that maintain pituitary sensitivity through a separate receptor pathway, are strategies used in research to maintain response magnitude over longer study periods.
Doxorubicin is a widely used chemotherapy agent whose clinical utility is limited by cumulative cardiotoxicity — it produces a dilated cardiomyopathy through oxidative stress, mitochondrial dysfunction, and apoptotic cardiomyocyte loss. This chemotherapy-induced cardiotoxicity model has been used as a research platform for Hexarelin because it creates robust, reproducible cardiac dysfunction in a short time frame without the technical challenges of surgical coronary artery ligation. Studies in rodent doxorubicin models have found that concurrent Hexarelin administration significantly reduces the degree of LV dilation, preserves ejection fraction, reduces cardiomyocyte apoptosis, and partially normalizes mitochondrial morphology and function compared to doxorubicin alone. The cardioprotective mechanism in this context is thought to involve anti-apoptotic Akt signaling through both GHS-R1a and CD36, along with PPARγ-driven upregulation of mitochondrial antioxidant enzymes including MnSOD. If these findings can be replicated and extended in larger animal models, they raise the possibility of Hexarelin or Hexarelin analogs as cardioprotective adjuncts during anthracycline chemotherapy — a clinically meaningful application given the prevalence of doxorubicin use in oncology.
In human GH stimulation research, single doses of Hexarelin have ranged from 0.5 to 2 µg/kg body weight administered subcutaneously or intravenously, with 1–2 µg/kg being the most commonly used range for maximal GH stimulation testing. These doses consistently produce peak serum GH concentrations of 30–80 ng/mL in healthy young adults, though responses are considerably lower in obese individuals (GH responses to GHRPs are blunted by obesity and associated somatostatin tone) and decline with age. In cardiac animal model studies, Hexarelin has been administered at doses of 80–100 µg/kg subcutaneously once or twice daily, which are substantially higher in relative terms than the GH stimulation doses used in humans — a scaling consideration that is relevant when interpreting animal cardioprotection data in a human research context.
Hexarelin is most commonly administered via subcutaneous injection in research settings. Intravenous administration produces a similar magnitude GH response but with faster onset and a more sharply peaked kinetic profile. Oral and intranasal delivery have been explored in the literature: oral bioavailability is low (typically <1% for the native peptide), and intranasal delivery has been studied as a non-invasive alternative with partial CNS delivery potential. For cardiac studies in animals, once or twice daily subcutaneous dosing has been the standard approach. Reconstituted solutions should be used promptly after preparation; the peptide is stable in lyophilized form at −20°C but has limited room-temperature solution stability due to susceptibility to oxidative degradation of the tryptophan residue.
Given the well-documented tolerance to Hexarelin’s GH-releasing effects with continuous administration, research designs intended to study sustained GH axis stimulation should incorporate tolerance management strategies. Options supported by the literature include: limiting continuous Hexarelin administration to no more than 7–14 days before a drug-free interval, alternating Hexarelin with GHS-R1a-independent GH secretagogues (e.g., GHRH analogs like CJC-1295), or using Hexarelin specifically for acute stimulation tests where a single-dose challenge rather than continuous treatment is the design. For research focused exclusively on CD36-mediated cardiac effects, tolerance to GH release is less relevant, as CD36 receptor desensitization appears to be substantially slower than GHS-R1a desensitization. Consult the AI Coach for detailed tolerance management protocol guidance.
Hexarelin lyophilized powder is typically reconstituted in bacteriostatic water or sterile saline. Given that the peptide contains a 2-methyltryptophan residue susceptible to oxidative degradation, reconstituted solutions should be stored at 4°C in amber vials and used within 2–3 weeks. Single-use aliquots frozen at −20°C are preferable for longer-term solution storage. Research-grade Hexarelin should meet ≥98% purity by HPLC (the high affinity for GHS-R1a means trace impurities could confound receptor-specific experimental designs) with mass spec verification of the correct molecular weight (887.1 Da). Use the peptide calculators for precise reconstitution volume and dosing calculations.
Human studies of Hexarelin for GH stimulation have generally shown a manageable acute safety profile. The most commonly reported adverse effects are transient and include facial flushing, mild nausea, brief elevation in blood pressure (attributed to GH-mediated vasoconstrictive effects and cortisol release), and injection site discomfort. Hexarelin, like other GHRPs, stimulates ACTH and cortisol release in addition to GH — an effect that is less pronounced with Ipamorelin and GHRP-2 but clinically relevant with Hexarelin at higher doses. Transient elevation in plasma cortisol following Hexarelin administration should be factored into research designs where cortisol levels are endpoint measures. Prolactin elevation has also been observed at pharmacological doses. These endocrine side effects are dose-dependent and typically resolve within 60–120 minutes of administration.
The cardiovascular effects of Hexarelin — while beneficial in the context of cardiac injury models — require consideration in research subjects without cardiac pathology. Hexarelin can produce modest acute increases in heart rate and blood pressure through sympathomimetic GH-mediated effects, and the vasodilatory coronary effects could theoretically cause hemodynamic changes in subjects with significant pre-existing coronary artery disease. In cardiac research, these cardiovascular effects are endpoints of interest; in endocrine research, they are potential confounds to monitor. No severe cardiovascular adverse events attributable specifically to Hexarelin have been reported in the published clinical research literature at doses used for GH stimulation testing.
Long-duration human safety data for Hexarelin are limited. The tolerance development that constrains chronic GH release research also means that most human studies have been short-duration designs, leaving chronic safety questions largely unaddressed. The combination of ACTH/cortisol stimulation with chronic dosing could be relevant to adrenal function in extended studies. Given that GHS-R1a is expressed in multiple peripheral tissues beyond the pituitary — including in gastrointestinal tissue, pancreas, and hypothalamic energy regulation circuits — chronic GHS-R1a stimulation could have metabolic and behavioral effects that warrant monitoring in extended studies. As with all peptide research, materials should be sourced from documented GMP-compliant suppliers with sterility and endotoxin certification for any in vivo application. Refer to the Peptide Database for the latest literature updates on Hexarelin safety.
Hexarelin produces a larger acute GH response than both GHRP-2 and GHRP-6 at equivalent doses in most published comparative studies, making it the most potent GH secretagogue in the synthetic GHRP family. However, Hexarelin also produces more cortisol and prolactin release than GHRP-2, and considerably more than Ipamorelin, which is more selective for GH release with minimal cortisol stimulation. Hexarelin is also the only GHRP with demonstrated CD36-mediated cardiac activity, making it uniquely positioned for cardiology research. The trade-off is faster tolerance development compared to GHRP-2 or Ipamorelin. The “best” GHRP depends entirely on the research application: for maximum acute GH response, Hexarelin; for selective GH release with minimal other hormone perturbation, Ipamorelin; for a balance, GHRP-2.
CD36 is a class B scavenger receptor expressed on cardiomyocytes, endothelium, vascular smooth muscle, macrophages, and platelets. In the heart, its most important canonical function is facilitating long-chain fatty acid uptake for mitochondrial beta-oxidation — the primary energy source for the healthy myocardium. CD36 is also a co-receptor for oxidized LDL, thrombospondin, and advanced glycation end products, making it a node for atherogenic and inflammatory signaling in the vasculature. Hexarelin binds CD36 with high affinity and activates intracellular signaling pathways (particularly Src kinase/PI3K/Akt and PPARγ activation) that produce cardioprotective gene expression changes. Because CD36 is a separate receptor from GHS-R1a, Hexarelin’s cardiac effects occur even in the absence of pituitary GH secretion — a fact confirmed in hypophysectomized animal studies that form the foundation of the CD36-cardiac pharmacology literature.
Tolerance to Hexarelin’s GH-releasing effects develops through two complementary mechanisms: downregulation and desensitization of GHS-R1a on pituitary somatotrophs (receptor-level tolerance), and compensatory upregulation of hypothalamic somatostatin secretion in response to the elevated GH levels (systems-level counter-regulation). The somatostatin upregulation is particularly important — even if GHS-R1a sensitivity is maintained, elevated somatostatin tone can blunt the GH response by opposing the stimulatory signals at the pituitary. Prevention strategies include limiting continuous use to 1–2 week periods with equivalent washout, co-administering somatostatin antagonists (research tools only, not clinically available), or alternating with GHRH analogs that don’t share the GHS-R1a pathway. For research focused on CD36-mediated cardiac endpoints, GH release tolerance is largely irrelevant.
Hexarelin stimulation tests have been studied as alternatives to insulin tolerance testing (ITT) for assessing GH reserve in suspected GH deficiency. The hexarelin challenge produces a robust GH response in subjects with intact pituitary function and a blunted response in verified GH deficiency, with sensitivity and specificity comparable to arginine-GHRH stimulation tests in some comparative studies. However, Hexarelin GH stimulation testing is not currently part of standard clinical endocrinology guidelines in most jurisdictions, where ITT, glucagon, and GHRH-arginine tests remain the preferred diagnostic tools. Hexarelin stimulation is used as a research assessment tool for GH secretory capacity in investigational studies.
As a potent GH secretagogue, Hexarelin would be expected to influence body composition through its effects on GH/IGF-1 levels — specifically by promoting lean mass accretion and (with longer-term elevation of IGF-1) potentially reducing adiposity. However, the tolerance development with chronic Hexarelin use substantially limits the sustained GH elevation that would be needed for meaningful body composition changes. Short-term acute GH responses, while large in magnitude, are unlikely to drive the persistent anabolic and lipolytic signaling that GH produces only with sustained elevation. Most body composition research using GH secretagogues has therefore used either pulsatile GHRH combinations or longer-acting secretagogues with less acute tolerance development.
GHS-R1a is expressed in multiple brain regions including the hippocampus, hypothalamus, and substantia nigra, and GHS-R1a activation by synthetic GHRPs including Hexarelin has been shown to have neuroprotective effects in rodent models of Parkinson’s disease (6-OHDA model) and excitotoxic injury. The proposed mechanisms include anti-apoptotic PI3K/Akt signaling, mitochondrial protective effects, and activation of anti-inflammatory microglial phenotypes. While Hexarelin has not been as extensively studied for neuroprotection as GHRP-6 (which has a more developed neuroprotection literature), the shared GHS-R1a mechanism means Hexarelin’s potential neuroprotective activity is biologically plausible and warrants investigation.
Hexarelin acts as a synthetic agonist at GHS-R1a — the same receptor activated by endogenous ghrelin. From the receptor’s perspective, Hexarelin and ghrelin produce qualitatively similar downstream signals, though with different kinetic and potency characteristics. One important difference is that ghrelin is acylated (octanoylated at Ser3), while Hexarelin is not — meaning ghrelin engages GOAT enzyme biology and energy sensing circuits that Hexarelin does not. Additionally, ghrelin has important roles in appetite stimulation and gastric motility via peripheral GHS-R1a and GHS-R1b receptors that may be engaged differently by Hexarelin. In research settings, Hexarelin is not typically used as a ghrelin mimetic for metabolic or appetite studies; its applications are focused on GH stimulation and cardiac protection where its receptor pharmacology and CD36 activity are the relevant features.
Disclaimer: This information is for research and educational purposes only. It is not medical advice. Consult a qualified healthcare professional before using any peptide.