D tier · weak
GHRP-6 is the prototype of the class and its pharmacology is well described, but it is also the least selective member: the same doses that release GH reliably raise ACTH, cortisol and appetite, it has no approval anywhere, no controlled outcome trial, and FDA has flagged compounded product for immunogenicity risk.
ghrp-6
GHRP-6 is the original synthetic hexapeptide ghrelin-receptor agonist and the compound from which GHRP-2, hexarelin and ipamorelin were derived. It raises growth hormone in humans, but does so alongside consistent ACTH and cortisol release and a pronounced appetite effect, and no trial has tested it against a clinical or body-composition endpoint.
// we supply this one
available as a research reagent
≥ 99% HPLC · lyophilised powder · batch certificate published. Grade D above is our own and is not adjusted because we stock it.
the explanation
GHRP-6 was the first peptide of its kind and it does make the body release growth hormone. The problem is that it is the least clean of the family — it also pushes up stress hormones and makes people notably hungrier, and no proper trial has ever shown it changes muscle, fat or health.
regulatory status
Not approved for human use in any jurisdiction
FDA placed GHRP-6 in Category 2 of nominated bulk drug substances, stating it 'may pose risk for immunogenicity for certain routes of administration due to the potential for aggregation and peptide-related impurities'; WADA prohibits GHRP-6 at all times under S2.2.4 alongside the rest of the GHRP class.
how it works · proposed mechanism
GHRP-6 is the prototype ghrelin mimetic, and its mechanism is inseparable from its off-target profile because both run through the same receptor.
The original GHS-R1a ligand
GHRP-6 was the compound whose GH-releasing activity led to the discovery of the growth hormone secretagogue receptor and, subsequently, of endogenous ghrelin itself. It acts synergistically with GHRH because the two engage independent receptor systems on the somatotroph.
HPA axis co-activation
The same GHS-R1a engagement that releases GH also drives corticotroph ACTH secretion and downstream cortisol. This is not a contaminant effect or a dose artefact — it reproduces across healthy volunteers, Cushing's disease, Addison's disease and thyrotoxicosis cohorts.
Strong orexigenic drive
As the least selective ghrelin mimetic in common use, GHRP-6 produces the most pronounced hunger signal of the class through hypothalamic arcuate-nucleus activation. Appetite stimulation is the single most consistently reported subjective effect.
Sleep architecture shift
Repetitive nocturnal GHRP-6 boluses increased stage 2 sleep from 245.4 ± 25.8 to 270.1 ± 25.3 minutes without increasing slow-wave sleep (Frieboes 1995). This is the opposite pattern to GHRH, which increases slow-wave sleep and suppresses cortisol.
what’s reported
evidence shape
6 sourcesThe composition of the cited literature by study type. This describes the shape of the evidence, not its quality — and it does not by itself set the grade.
⚠ the catch
Every later peptide in this family — hexarelin, GHRP-2, and above all ipamorelin, which was explicitly developed and published as 'the first selective growth hormone secretagogue' — exists because GHRP-6's ACTH, cortisol and prolactin spillover was considered a defect worth engineering out. Choosing GHRP-6 today means accepting the exact off-target burden the field spent thirty years designing around, in exchange for no outcome evidence whatsoever.
key published findings
- Human PK study (Cabrales 2013, Eur J Pharm Sci, n=9 healthy males, IV boluses of 100, 200 and 400 µg/kg): biphasic kinetics with distribution half-life 7.6 ± 1.9 min and elimination half-life 2.5 ± 1.1 h; dose-proportional AUC; atypical concentration spikes during the elimination phase in 4 of 9 subjects.
- Human sleep-lab study (Frieboes 1995, Neuroendocrinology, healthy men, repetitive IV GHRP-6 vs placebo): nocturnal GH rose to 15.4 ± 9.6 ng/mL versus 5.5 ± 4.0 ng/mL on placebo (p<0.02), with concurrent elevation of ACTH and cortisol and an increase in stage 2 sleep to 270.1 ± 25.3 min versus 245.4 ± 25.8 min (p<0.02) — GH and stress-axis activation in the same subjects, same night.
- Human endocrine study (Oliveira 2003, J Endocrinol Invest, n=10 Cushing's disease patients): GHRP-6 significantly raised ACTH from a baseline of 15.5 to a peak of 45.1 pmol/L and cortisol from 583.0 to 1013.4 nmol/L, a response comparable to DDAVP — the clearest quantification of GHRP-6's corticotroph activity, though obtained in a disease cohort rather than healthy volunteers.
- Human route-comparison study (Frieboes 1999, J Neuroendocrinol): intranasal GHRP-6 significantly raised nocturnal GH with a concurrent trend toward increased first-half-night ACTH secretion; effects were dependent on dose, duration and route, with oral and sublingual routes performing worse than intranasal.
- Swine and rat comparison (Raun 1998, Eur J Endocrinol): in conscious swine, 'administration of both GHRP-6 and GHRP-2 resulted in increased plasma levels of ACTH and cortisol', whereas ipamorelin at doses more than 200-fold above its GH ED50 did not — the finding that made ipamorelin 'the first GHRP-receptor agonist with a selectivity for GH release similar to that displayed by GHRH', and that establishes GHRP-6's corticotroph activity as a recognised, deliberately designed-around defect. Notably, none of the secretagogues tested altered prolactin, FSH, LH or TSH in that swine model.
- Regulatory (FDA, Category 2 bulk drug substances): GHRP-6 'may pose risk for immunogenicity for certain routes of administration due to the potential for aggregation and peptide-related impurities.'
limitations of the evidence
- The best-quantified cortisol and ACTH data come from patients with Cushing's disease, thyrotoxicosis, Addison's disease and type 1 diabetes rather than from healthy adults, so the magnitude of HPA activation at typical exposures in healthy people is inferred rather than directly measured.
- The prolactin picture is genuinely inconsistent and should not be overstated: in humans, GHRP-2 and hexarelin produced significant but sub-TRH prolactin responses (Arvat 1997), while in conscious swine none of the secretagogues tested — GHRP-6 included — altered prolactin, FSH, LH or TSH (Raun 1998); GHRP-6-specific prolactin magnitudes in healthy adults have not been established.
- There is no randomised controlled trial of GHRP-6 with body composition, strength, injury recovery or any clinical endpoint as a primary outcome — the entire human literature is acute endocrine and pharmacokinetic testing.
documented safety signals
- Reproducible ACTH and cortisol elevation across multiple independent human cohorts, including a near-doubling of peak cortisol in one clinical study.
- Pronounced appetite stimulation via arcuate GHS-R1a activation — the most consistent subjective effect and directly counterproductive for fat-loss goals.
- Prolactin and cortisol elevations are catalogued among the reported adverse effects of self-administered GH-axis peptides in the 2026 Frontiers in Endocrinology review, alongside appetite changes, dysglycaemia and fluid retention.
- FDA Category 2 designation citing immunogenicity risk from aggregation and peptide-related impurities in compounded product.
- Unexplained plasma concentration spikes during the elimination phase in 4 of 9 subjects in the only published human PK study, indicating incompletely characterised disposition.
identity
| full name | Growth Hormone-Releasing Peptide-6 |
| category | Growth Hormone |
| modality | peptide |
| formula | C46H56N12O6 |
| molar mass | 873.02 g/mol |
| cas | 87616-84-0 |
| half-life | ~7.6 min distribution, ~2.5 h elimination (IV) |
| sequence | His-D-Trp-Ala-Trp-D-Phe-Lys-NH2 (C-terminally amidated) |
laboratory handling
| storage | Lyophilised powder is stored at -20 °C, desiccated and protected from light; reconstituted aqueous solution is refrigerated at 2-8 °C for short-term laboratory use or aliquoted and stored at -20 °C to avoid repeated freeze-thaw cycles. |
| solubility | Soluble in sterile or bacteriostatic water and in aqueous buffers; dilute acetic acid or DMSO is used for concentrated laboratory stock solutions. |
| co-studied with | GHRP-6 is most often studied in combination with a GHRH analogue, since the two receptor systems are independent and the combined GH pulse exceeds either alone — but combining also compounds the HPA-axis and appetite effects rather than offsetting them. |
Handling information describes laboratory practice for a research reagent. It is not a preparation guide for use in humans.
the receipts
6 citedU.S. Food and Drug Administration · 2023 · official
European Journal of Pharmaceutical Sciences · 2013 · peer-reviewed
Neuroendocrinology · 1995 · peer-reviewed
Journal of Endocrinological Investigation · 2003 · peer-reviewed
Frontiers in Endocrinology · 2026 · review
European Journal of Endocrinology · 1998 · preclinical
others in Growth Hormone