Hexarelin

This is hexarelin’s strongest and most human evidence base — and also the application that contains its own refutation.

The acute effect is real and well characterized. In healthy adult men, IV hexarelin releases GH dose-dependently and more potently than GHRH, with marked synergy when the two are given together ^{1,2Reference 1Massoud AF et al. · 1996Clinical trialHexarelin-induced growth hormone, cortisol, and prolactin release: a dose-response study — human (clinical trial)View study →Reference 2Massoud AF et al. · 1996Clinical trialThe effect of repeated administration of hexarelin, a growth hormone releasing peptide, and growth hormone releasing hormone on growth hormone responsivity — human (clinical trial)View study →}. In children and GH-deficient patients — idiopathic GH deficiency, homozygous β-thalassemia, and various hypothalamic-pituitary abnormalities — it reliably stimulates GH ^{3,4Reference 3Loche S et al. · 1995Clinical trialThe effect of hexarelin on growth hormone (GH) secretion in patients with GH deficiency — human (clinical trial)View study →Reference 4Tolis G et al. · 1997Clinical trialGrowth hormone release by the novel GH releasing peptide hexarelin in patients with homozygous beta-thalassemia — human (clinical study)View study →}; the response is reproducible within individuals and augmented by sex steroids in childhood ^{5Reference 5Loche S et al. · 1997The growth hormone response to hexarelin in children: reproducibility and effect of sex steroids — human (children)View study →}, and it is blunted by higher body-fat mass and by aging ^{10,11Reference 10Arvat E et al. · 1997ReviewAge-related growth hormone-releasing activity of growth hormone secretagogues in humans — reviewView study →Reference 11Rahim A et al. · 1998The effect of body composition on hexarelin-induced growth hormone release in normal elderly subjects — humanView study →}. Importantly, hexarelin is not GH-selective: it acutely raises ACTH, cortisol and prolactin as well ^{12Reference 12Maccario M et al. · 2002RCTImpact of two or three daily subcutaneous injections of hexarelin, a synthetic growth hormone (GH) secretagogue, on 24-h GH, prolactin, adrenocorticotropin and cortisol secretion in humans — human (randomised clinical trial)View study →}, and when given repeatedly during sleep in healthy volunteers it stimulated GH, ACTH, cortisol and prolactin while decreasing slow-wave sleep ^{15Reference 15Frieboes RM et al. · 2004Clinical trialHexarelin decreases slow-wave sleep and stimulates the secretion of GH, ACTH, cortisol and prolactin during sleep in healthy volunteers — human (controlled clinical trial)View study →}.

The chronic effect is where it falls apart. Twelve healthy elderly subjects received 1.5 µg/kg subcutaneously twice daily for 16 weeks. The area under the GH curve fell from 19.1 µg/L·h at baseline to 13.1 at week 1, 12.3 at week 4 and 10.5 at week 16 — a significant decline by week 4 and a highly significant one by week 16. Four weeks after stopping, it returned to 19.4, statistically indistinguishable from baseline, so the desensitization is partial and reversible ^{13,14Reference 13Rahim A · 1998Clinical trialDoes desensitization to hexarelin occur? — human (clinical trial; same 12-subject 16-week dataset as reference 14)View study →Reference 14Rahim A et al. · 1998Clinical trialGrowth hormone status during long-term hexarelin therapy — human (clinical trial, 16 weeks; null for IGF-1, body composition and BMD)View study →}. (These two references report the same 12-subject dataset — a full paper and a conference-proceedings version — and are cited together throughout rather than as independent replications.) Over the full 20 weeks, serum IGF-1 and IGFBP-3 did not change, and total body fat, lean body mass and bone mineral density were all unchanged at week 16 ^{14Reference 14Rahim A et al. · 1998Clinical trialGrowth hormone status during long-term hexarelin therapy — human (clinical trial, 16 weeks; null for IGF-1, body composition and BMD)View study →}. The investigators concluded that the biological impact of this schedule on the GH–IGF-1 axis appeared minimal.

That is the whole therapeutic problem in one study: the pituitary stops responding, and even before it does, the downstream axis the GH pulse is supposed to drive never moves.

Gap: the human data are abundant but are almost entirely acute pharmacodynamic and diagnostic-test data. There is no approved indication and no demonstrated clinical outcome, and the single chronic study is 12 subjects — enough to establish that tachyphylaxis occurs, not enough to characterize it across doses, schedules or populations. Whether an intermittent or lower-dose schedule could avoid desensitization has never been tested.

Small human studies consistently report that a single IV dose of hexarelin (2 µg/kg) produces a short-lived rise in left-ventricular ejection fraction, and — this is the interesting part — that it does so without going through growth hormone.

In healthy men, LVEF rose measurably within 15–30 minutes without change in blood pressure or heart rate, an effect not reproduced by recombinant GH at matched GH levels ^{6Reference 6Bisi G et al. · 1999Acute cardiovascular and hormonal effects of GH and hexarelin, a synthetic GH-releasing peptide, in humans — human (acute haemodynamic study)View study →}.

The cleanest demonstration of GH-independence comes from hypopituitary adults: in seven GH-deficient men, the GH response to hexarelin was negligible (peak 1.9 vs 45.7 µg/L in controls) yet LVEF still rose (50 → 57%), with no change in catecholamines, blood pressure or cardiac output ^{8Reference 8Bisi G et al. · 1999Cardiac effects of hexarelin in hypopituitary adults — human (acute study, GH-deficient adults)View study →}.

A companion study in 7 normal adults, 7 severe GH-deficient patients and 12 patients with dilated cardiomyopathy found the same: LVEF rose significantly in the normal and GH-deficient groups — but not in the dilated-cardiomyopathy group ^{7Reference 7Broglio F et al. · 2001Clinical trialGrowth hormone-independent cardiotropic activities of growth hormone-releasing peptides in normal subjects, in patients with growth hormone deficiency, and in patients with idiopathic or ischemic dilated cardiomyopathy — human (acute study; null in dilated cardiomyopathy)View study →}.

In a controlled study of coronary-artery-disease patients undergoing bypass surgery, hexarelin — but not GHRH, recombinant GH or placebo — acutely improved cardiac index and output ^{9Reference 9Broglio F et al. · 2002Clinical trialEffects of acute hexarelin administration on cardiac performance in patients with coronary artery disease during by-pass surgery — human (controlled clinical trial)View study →}.

A useful contrast: a physiological dose of human ghrelin itself produced no acute cardiac effect in severe GH-deficient patients, distinguishing hexarelin’s action from simple ghrelin-receptor agonism ^{16Reference 16Janssen JA et al. · 2004Clinical trialThere are no acute cardiac effects of a single iv dose of human ghrelin in severe growth hormone deficient patients — human (clinical study; negative control for hexarelin’s effect)View study →}.

Gap: every one of these is an acute hemodynamic study with a surrogate endpoint (LVEF), n = 7–24, in a research setting, from a small number of connected groups in Turin. None measured symptoms, exercise capacity, hospitalization or survival, none dosed beyond a single administration, and the effect was absent in the one diseased cardiac population tested — which is precisely the population a cardiac therapy would target. There has never been a hexarelin cardiac outcome trial.

A multi-laboratory rodent literature reports that chronic hexarelin protects the heart, and does so independently of GH. In 24-month-old rats, 21 days of subcutaneous hexarelin produced near-complete recovery of post-ischemic left-ventricular developed pressure (90% of pre-ischemic values vs 37% in controls) and cut creatine-kinase leakage — outperforming GH itself, and, critically, “divorced from any detectable alteration of somatotropic function” as measured by pituitary GH mRNA and plasma IGF-1 ^{17Reference 17Rossoni G et al. · 1998AnimalProtectant activity of hexarelin or growth hormone against postischemic ventricular dysfunction in hearts from aged rats — animal (rat)View study →}.

Hexarelin improved cardiac function and remodeling after experimental myocardial infarction in rats ^{18Reference 18Tivesten A et al. · 2000AnimalThe growth hormone secretagogue hexarelin improves cardiac function in rats after experimental myocardial infarction — animal (rat)View study →}; protected cardiomyocytes from doxorubicin-induced death and from calcium-paradox injury, the latter again where GH did not ^{19,20Reference 19Filigheddu N et al. · 2001In vitroHexarelin protects H9c2 cardiomyocytes from doxorubicin-induced cell death — in vitroView study →Reference 20Torsello A et al. · 2001In vitroHexarelin, but not growth hormone, protects heart from damage induced in vitro by calcium deprivation replenishment — animal (rat, ex vivo)View study →}; attenuated cardiac fibrosis and hypertrophy in spontaneously hypertensive rats ^{22Reference 22Xu X et al. · 2012AnimalChronic administration of hexarelin attenuates cardiac fibrosis in the spontaneously hypertensive rat — animal (rat)View study →}; and preserved cardiac morphology and function after ischemia-reperfusion in mice via neuroinflammatory and autonomic pathways ^{23Reference 23McDonald H et al. · 2020AnimalHexarelin targets neuroinflammatory pathways to preserve cardiac morphology and function in a mouse model of myocardial ischemia-reperfusion — animal (mouse)View study →}.

One mouse study reported that even a single oral dose given acutely after MI protected chronic cardiac function ^{24Reference 24Mao Y et al. · 2014AnimalOne dose of oral hexarelin protects chronic cardiac function after myocardial infarction — animal (mouse)View study →} — striking, though hard to reconcile with ~0.3% oral bioavailability in humans.

Mechanistically, the myocardial target was identified as CD36, a receptor distinct from pituitary GHS-R1a: a photoactivatable hexarelin derivative labeled an 84-kDa cardiac binding protein whose N-terminal sequence was identical to rat CD36, and the response was absent in CD36-null mice and in CD36-deficient hypertensive rats ^{25,27Reference 25Bodart V et al. · 1999AnimalIdentification and characterization of a new growth hormone-releasing peptide receptor in the heart — animal (rat; receptor identification and coronary vasoconstriction)View study →Reference 27Bodart V et al. · 2002AnimalCD36 mediates the cardiovascular action of growth hormone-releasing peptides in the heart — animal (rat/mouse; coronary vasoconstriction, proposed vasospasm mechanism)View study →}. This is real, well-executed receptor pharmacology and it is reviewed in detail elsewhere ^{43Reference 43Mao Y et al. · 2014ReviewThe cardiovascular action of hexarelin — reviewView study →}.

Two honest caveats belong with it. First, the functional readout in both CD36 papers was coronary vasoconstriction — hexarelin raised coronary perfusion pressure dose-dependently, and the authors proposed CD36 as a mediator of the coronary vasospasm seen in hypercholesterolemia and atherosclerosis ^{25,27Reference 25Bodart V et al. · 1999AnimalIdentification and characterization of a new growth hormone-releasing peptide receptor in the heart — animal (rat; receptor identification and coronary vasoconstriction)View study →Reference 27Bodart V et al. · 2002AnimalCD36 mediates the cardiovascular action of growth hormone-releasing peptides in the heart — animal (rat/mouse; coronary vasoconstriction, proposed vasospasm mechanism)View study →}. These are receptor-identification and vasoactivity papers, not cardioprotection papers; the same mechanism that underwrites the metabolic story is a plausible cardiac liability. Second, the widely cited heart-failure result treated four different GHRPs together — GHRP-1, GHRP-2, GHRP-6 and hexarelin, all at 100 µg/kg — and reported outcomes for “GHRP treatment” as a class, so it cannot be attributed to hexarelin specifically ^{21Reference 21Xu XB et al. · 2005AnimalGH-releasing peptides improve cardiac dysfunction and cachexia and suppress stress-related hormones and cardiomyocyte apoptosis in rats with heart failure — animal (rat; pooled GHRP-1/-2/-6 and hexarelin, class-level result)View study →}. (That study does contain a genuinely GH-independent observation: GHRP reduced myocardial creatine-kinase release in hypophysectomized rats subjected to acute ischemia.)

Gap: entirely animal and in-vitro. No human cardioprotection outcome trial exists, and the acute human inotropy data are the only bridge — small, acute, surrogate, and null in cardiomyopathy. A mechanism this well characterized has had 25 years to produce a clinical trial and has not.

In macrophages and rodents, hexarelin binds the scavenger receptor CD36 and, through a PPARγ-dependent pathway, up-regulates the cholesterol-efflux transporters ABCA1 and ABCG1 and reduces foam-cell formation; treating ApoE-null mice on a lipid-rich diet with hexarelin significantly reduced atherosclerotic lesions, and the response was strongly impaired in PPARγ-heterozygous macrophages ^{26Reference 26Avallone R et al. · 2006In vitroA growth hormone-releasing peptide that binds scavenger receptor CD36 and ghrelin receptor up-regulates sterol transporters and cholesterol efflux in macrophages through a PPARγ-dependent pathway — in vitro / animal (ApoE-null mouse)View study →}. Chronic hexarelin suppressed plaque development in a high-lipid-diet/vitamin-D₃ rat model ^{28Reference 28Pang J et al. · 2010AnimalHexarelin suppresses high lipid diet and vitamin D3-induced atherosclerosis in the rat — animal (rat)View study →}, and attenuated atherosclerosis in ApoE-knockout mice by inhibiting LOX-1/NF-κB-mediated uptake of oxidized LDL by macrophages ^{29Reference 29Cheng XL et al. · 2019AnimalHexarelin attenuates atherosclerosis via inhibiting LOX-1-NF-κB signaling pathway-mediated macrophage ox-LDL uptake in ApoE−/− mice — animal (mouse)View study →}.

Gap: animal and in-vitro only — no human lipid, imaging or cardiovascular-event data of any kind. And the receptor biology genuinely cuts both ways: the same CD36 binding that reduces macrophage lipid uptake produces coronary vasoconstriction in perfused hearts, which the same research group proposed as a vasospasm mechanism in exactly the atherosclerotic setting this application targets ^{25,27Reference 25Bodart V et al. · 1999AnimalIdentification and characterization of a new growth hormone-releasing peptide receptor in the heart — animal (rat; receptor identification and coronary vasoconstriction)View study →Reference 27Bodart V et al. · 2002AnimalCD36 mediates the cardiovascular action of growth hormone-releasing peptides in the heart — animal (rat/mouse; coronary vasoconstriction, proposed vasospasm mechanism)View study →}.

Working through CD36, hexarelin induced a brown-fat-like phenotype in mouse 3T3-L1 white adipocytes and in the epididymal white fat of treated mice — depletion of intracellular lipid, dense mitochondrial cristae formation, raised cytochrome-c-oxidase activity, and up-regulation of the thermogenic markers PGC-1α and UCP-1. The in-vivo effect was lost in CD36-null mice, tying it to the scavenger receptor rather than to GH ^{30Reference 30Rodrigue-Way A et al. · 2007In vitroA growth hormone-releasing peptide promotes mitochondrial biogenesis and a fat burning-like phenotype through scavenger receptor CD36 in white adipocytes — in vitro / animal (mouse)View study →}.

In non-obese insulin-resistant MKR mice, hexarelin improved glucose and insulin tolerance and lowered plasma and liver triglycerides while shifting body composition toward lean mass ^{31Reference 31Mosa R et al. · 2017AnimalHexarelin, a growth hormone secretagogue, improves lipid metabolic aberrations in nonobese insulin-resistant male MKR mice — animal (mouse)View study →}.

A related study found hexarelin protected rodent pancreatic β-cell function against streptozotocin cytotoxicity via mitochondrial anti-apoptotic pathways ^{32Reference 32Zhao Y et al. · 2016In vitroHexarelin protects rodent pancreatic β-cells function from cytotoxic effects of streptozotocin involving mitochondrial signalling pathways — animal (rat) / in vitroView study →}.

Gap: animal and in-vitro only — there is no human metabolic, glycemic or fat-loss trial. This mechanism is the entire scientific basis for community “fat-loss” marketing, and the one human study that actually measured the outcome found total body fat unchanged after 16 weeks of twice-daily dosing ^{14Reference 14Rahim A et al. · 1998Clinical trialGrowth hormone status during long-term hexarelin therapy — human (clinical trial, 16 weeks; null for IGF-1, body composition and BMD)View study →}. A mouse adipocyte phenotype is not a human fat-loss result, and here the human result already points the other way.

In rats, hexarelin (alongside the related GH secretagogue JMV2894) protected skeletal muscle from mitochondrial damage in a cisplatin-induced cachexia model, preserving mitochondrial biogenesis markers (PGC-1α, NRF-1, TFAM, mtDNA) and limiting autophagy and ROS markers ^{33Reference 33Sirago G et al. · 2017AnimalGrowth hormone secretagogues hexarelin and JMV2894 protect skeletal muscle from mitochondrial damages in a rat model of cisplatin-induced cachexia — animal (rat)View study →}.

In aged dogs, 16 weeks of hexarelin produced changes in the somatotropic axis and muscle morphology ^{34Reference 34Cella SG et al. · 1996Sixteen weeks of hexarelin therapy in aged dogs: effects on the somatotropic axis, muscle morphology, and bone metabolism — animal (dog)View study →}.

GHRP-class peptides were also reported to alleviate cardiac cachexia in heart-failure rats — but that study pooled GHRP-1, -2, -6 and hexarelin and reported results for the class, so it is not hexarelin-specific evidence ^{21Reference 21Xu XB et al. · 2005AnimalGH-releasing peptides improve cardiac dysfunction and cachexia and suppress stress-related hormones and cardiomyocyte apoptosis in rats with heart failure — animal (rat; pooled GHRP-1/-2/-6 and hexarelin, class-level result)View study →}.

Gap: animal only, and thin even there — one rat cachexia model, one dog study, and a pooled-GHRP result. There is no human cachexia, sarcopenia or muscle-building trial. The bodybuilding use has no controlled human evidence at all, and the only chronic human study to measure lean body mass found no change ^{14Reference 14Rahim A et al. · 1998Clinical trialGrowth hormone status during long-term hexarelin therapy — human (clinical trial, 16 weeks; null for IGF-1, body composition and BMD)View study →}.

This row is scored low because of human data, not for lack of it.

The animal signal is genuine: in gonadectomized (osteopenic) male rats, 30 days of hexarelin prevented the androgen-deficiency-driven rise in bone-resorption markers and the fall in bone mineral density at the femur and lumbar vertebrae, with evidence that it inhibits resorption through a route beyond its GH-releasing action ^{35Reference 35Sibilia V et al. · 1999AnimalHexarelin, a growth hormone-releasing peptide, counteracts bone loss in gonadectomized male rats — animal (rat)View study →}. Aged dogs treated for 16 weeks showed changes in bone metabolism alongside somatotropic and muscle effects ^{34Reference 34Cella SG et al. · 1996Sixteen weeks of hexarelin therapy in aged dogs: effects on the somatotropic axis, muscle morphology, and bone metabolism — animal (dog)View study →}.

It did not translate. In the only long-term human study — 12 healthy elderly subjects, 1.5 µg/kg subcutaneously twice daily for 16 weeks — bone mineral density did not change (nor did total body fat or lean body mass). Of the several bone formation and resorption markers measured, only the C-terminal propeptide of type I collagen moved at all ^{14Reference 14Rahim A et al. · 1998Clinical trialGrowth hormone status during long-term hexarelin therapy — human (clinical trial, 16 weeks; null for IGF-1, body composition and BMD)View study →}.

Gap: a well-evidenced human negative that outweighs the rodent data for translational purposes. The honest caveats are that the human study was small (n=12), ran only 16 weeks — short for a BMD endpoint — and was conducted in healthy elderly subjects rather than an osteoporotic population, and that GH-response tachyphylaxis over that same window may itself explain the null. No osteoporosis trial has ever been run.

The evidence here is a single animal study. In golden hamsters subjected to optic-nerve transection, daily intraperitoneal hexarelin for five days dose-dependently increased retinal ganglion cell survival at seven days — 51.2% in saline controls versus 62.4%, 68.5% and 74.6% at 25, 50 and 100 µg/kg, with twice-daily dosing raising survival further ^{36Reference 36Chow KBS · 2026Hexarelin promotes the survival of retinal ganglion cells after optic nerve transection — animal (hamster)View study →}. The authors attribute this to the known anti-apoptotic signaling of GHS-R1a agonism.

Gap: one model, one laboratory, one species, no replication and no human neurological data of any kind. Community claims of neuroprotective or cognitive benefit have nothing else behind them, and are not scored here.