hexarelin: the synthetic GH secretagogue hexapeptide

hexarelin (also called examorelin, developmental code EP-23905) is a synthetic hexapeptide growth hormone secretagogue. it was developed in the 1990s as part of efforts to create orally or parenterally active small molecules that could stimulate GH release without requiring growth hormone itself. it acts primarily at the ghrelin receptor (GHSR-1a) in the pituitary and hypothalamus, and secondarily at the CD36 scavenger receptor in cardiovascular tissue. it has not received FDA or EMA approval and remains a research peptide.

what is hexarelin?

hexarelin is a six-amino-acid synthetic peptide with the sequence His-D-2-MeTrp-Ala-Trp-D-Phe-Lys-NH2. its design incorporates D-amino acids that confer proteolytic resistance relative to endogenous peptides. it belongs to the growth hormone releasing peptide (GHRP) family that includes GHRP-2, GHRP-6, and ipamorelin.

the GHRP family emerged from structure-activity studies on met-enkephalin in the 1980s, and hexarelin was among the first synthetic GHRPs shown to be potent GH releasers in humans. it stimulates GH release synergistically with GHRH, meaning that when co-administered with a GHRH analog, GH output is greater than either alone. early Phase 1 and Phase 2 studies in the 1990s documented robust GH release following subcutaneous administration in healthy adults, elderly patients, and GH-deficient subjects, cementing its pharmacological identity as the most potent GH-releasing peptide in the GHRP series [1].

despite its clear pharmacological activity, hexarelin was never taken through Phase 3 trials and was never approved. its development was eventually discontinued in favor of orally active small-molecule ghrelin mimetics and other approaches. it persists as a research tool and gray-market research peptide.

how does it work?

hexarelin activates the ghrelin receptor (GHSR-1a) on somatotrope cells in the anterior pituitary, triggering calcium mobilization and GH secretion. it also binds CD36, a scavenger receptor in cardiac and vascular tissue, which mediates cardiovascular effects independent of GH release.

the GHSR-1a mechanism is shared with endogenous ghrelin, which is why the GHRP family was renamed "ghrelin mimetics" after ghrelin's discovery in 1999. hexarelin is not structurally identical to ghrelin, but both activate the same receptor and produce overlapping downstream effects: GH release, appetite stimulation, and metabolic effects. unlike endogenous ghrelin, hexarelin does not require acylation for receptor binding, which is one reason it was easier to work with as a research compound. Mao and colleagues provided a useful overview of hexarelin's cardiovascular pharmacology in 2014 [2].

the CD36 pathway is the most pharmacologically distinctive feature of hexarelin relative to its GHRP relatives. CD36 is a scavenger receptor expressed in macrophages, platelets, cardiomyocytes, and endothelial cells. hexarelin binding at CD36 in animal models has been associated with reduced lipid accumulation and cardioprotective effects in ischemia-reperfusion injury, effects that appear to be at least partly independent of GH or IGF-1 changes. Mosa and colleagues reviewed the implications of hexarelin and ghrelin in diabetes and diabetes-associated heart disease, providing context for this receptor biology [3].

one limitation of hexarelin relative to ipamorelin is that it non-selectively stimulates cortisol and prolactin alongside GH, particularly at higher concentrations. this off-target endocrine activation is the main reason ipamorelin is generally considered the cleaner GH secretagogue for most research applications [4].

what does the evidence show?

Phase 1 and Phase 2 human studies in the 1990s demonstrated robust GH release, a modest but real IGF-1 increase, and cardiovascular effects in small patient populations. the evidence does not extend to large controlled outcome trials; no Phase 3 program was completed.

the early clinical pharmacology literature on hexarelin is primarily composed of small studies from Italian endocrinology groups (Ghigo, Arvat, Camanni at Turin) that characterized its GH-releasing properties across age groups, metabolic states, and in comparison with GHRH. Camanni, Ghigo, and Arvat provided a comprehensive review of the GHRP class in 1998 that remains a reference point for understanding where hexarelin fits within its family [5]. Maccario and colleagues later characterized the 24-hour GH secretion profile in humans under repeated hexarelin dosing [6], establishing the pulsatile pattern and the degree of prolactin and cortisol co-stimulation.

a parallel literature on cardiovascular effects exists, largely in rodent and ex-vivo models. the cardioprotective signals in ischemia-reperfusion and the CD36-mediated effects on lipid metabolism in animal models have attracted sustained research interest, but human outcome data in cardiac populations is limited to early-phase exploratory studies with no approved cardiovascular indication.

the review by Sigalos and Pastuszak in 2018 on the safety and efficacy of GH secretagogues provides a useful contemporaneous assessment of where the GHRP class stands across the evidence spectrum [4]. the honest summary is: hexarelin has clear pharmacological activity in humans and interesting preclinical cardiovascular signals, but no Phase 3 dataset, no approved indication, and no recent large human trials.

regulatory status and safety

hexarelin is not approved by the FDA, EMA, MHRA, TGA, or any major regulatory body. it is on the WADA prohibited list under S2 (peptide hormones and growth factors). safety data in humans comes from small Phase 2 studies conducted in the 1990s; long-term safety is uncharacterized.

the stimulation of cortisol and prolactin alongside GH is the most consistently documented neuroendocrine limitation. in short-term human studies, these elevations were transient and returned to baseline, but chronic effects in prolonged use are not known. at the concentrations studied in early clinical work, hexarelin was generally well tolerated, with injection-site reactions and mild transient hormonal perturbations as the main reported adverse effects.

like all GH-axis peptides, hexarelin is prohibited in WADA-governed competitive sport at all times under the S2.2 category covering growth hormone releasing factors. any competitive athlete subject to anti-doping rules should treat hexarelin as prohibited regardless of the route of administration.

where it fits among GH secretagogues

hexarelin sits in the GHRP/ghrelin receptor agonist branch of the GH axis, alongside ipamorelin, GHRP-2, and GHRP-6. it is the most potent GH releaser in the series but the least selective due to cortisol and prolactin co-stimulation. the GHRH-receptor branch (sermorelin, CJC-1295, tesamorelin) works at a different receptor and produces a different pulse profile.

the most common comparison is with ipamorelin, which shares the GHSR-1a mechanism but has a substantially more selective GH-only profile. ipamorelin has become the dominant GHRP in research and community use largely because of that selectivity, despite hexarelin's superior GH potency on a per-mole basis. GHRP-2 and GHRP-6 are structurally related but differ in their appetite-stimulatory and cortisol profiles; GHRP-6 in particular drives notable appetite stimulation via the ghrelin pathway. on the GHRH-receptor side, sermorelin and CJC-1295 work by amplifying hypothalamic input rather than bypassing it. combining a GHRP with a GHRH analog produces synergistic GH release, which is the mechanistic rationale behind combination stacks, though no controlled human safety data exists for such combinations.