What GHRP-6 is and how it works
GHRP-6, short for growth hormone releasing peptide 6, is a hexapeptide with the sequence His-D-Trp-Ala-Trp-D-Phe-Lys-NH₂. It came from work by the endocrinologist Cyril Bowers at Tulane University and the chemist Frank Momany, who started from met-enkephalin analogues that released growth hormone (GH) from pituitary tissue without acting as opioids, and used conformational energy calculations to choose the next variants to make. By the early 1980s that work had produced GHRP-6.
What made it unusual was that nobody knew what it bound to. It plainly did not act through the receptor for growth hormone-releasing hormone (GHRH): GHRH raises cyclic AMP in the pituitary cells that make GH, while GHRP-6 works through phospholipase C and a rise in intracellular calcium, and the two together released far more GH than either alone. Merck researchers cloned the target in 1996, a G-protein-coupled receptor now called GHS-R1a. Three years later Kojima, Kangawa and colleagues isolated its natural ligand from rat stomach and named it ghrelin. For more than a decade, GHRP-6 had been a synthetic key with no known lock.
GHRP-6 acts at two levels. In the anterior pituitary it stimulates the somatotroph cells that make GH; in the hypothalamus it increases release of the body's own GHRH and counters somatostatin, which holds GH secretion back. The hypothalamic part matters: where the pituitary is disconnected from the hypothalamus, the GH response largely disappears. The same receptor sits in the brain circuits that control feeding, which explains the other defining property of GHRP-6, a marked rise in appetite. It became the benchmark for later compounds, among them GHRP-2 and hexarelin, its methylated relative.
What the research on GHRP-6 shows
Most of the human literature is physiological: small studies built around a single intravenous injection, in healthy volunteers or in patients with pituitary or hypothalamic disease. They established that GHRP-6 releases GH reliably in people, and that GHRH plus GHRP-6 releases far more GH than the sum of the two given separately. That more-than-additive response became a diagnostic test for GH deficiency in adults, a combined bolus of both peptides. Evidence level: acute human physiology, not treatment trials.
The appetite effect appeared early in rats, where GHRP-6 injected into the brain increased eating at doses that did not change blood GH. It made sense once ghrelin turned out to rise before meals and to increase food intake in healthy volunteers. In GHRP-6 both effects run through one receptor, so a study of GH release involves the feeding pathway as well. Our comparison of growth hormone secretagogues sets this profile against the rest of the class.
Researchers have also used GHRP-6 outside the pituitary: a Cuban group, for instance, reported less heart-muscle damage with it in an animal model of myocardial infarction. Evidence level: animal models from a small number of laboratories.
What has not been shown matters as much: there are no long-term controlled trials of GHRP-6 for any outcome, and no approved medical use anywhere.
GHRP-6 doses used in published research
| Setting | Subjects | Route and schedule | Main read-out |
|---|---|---|---|
| Pituitary cell studies | Rat pituitary cells | Added to the culture medium, often with GHRH | GH release, signalling |
| Feeding studies | Rats | Injection into the brain ventricles, or systemic | Food intake, blood GH |
| Human physiology | Healthy adults; pituitary or hypothalamic disease | Single intravenous bolus in µg/kg, alone or with GHRH | GH over the next hour or two |
| Diagnostic research | Adults with suspected GH deficiency | Combined bolus of GHRH and GHRP-6 | Peak GH against a cut-off |
| Treatment trials | None published | – | – |
The human work used one-off stimulation tests with doses in micrograms per kilogram of body weight. They were designed to probe the GH axis on a single morning, not to test repeated dosing. No validated human dose of GHRP-6 exists. The table describes how GHRP-6 has been studied; it is not an instruction for use.
GHRP-6 safety and side effects
Safety information comes from short human studies and from what is known about the ghrelin receptor and about growth hormone excess. Long-term data do not exist.
- Appetite. Increased hunger is the expected result of ghrelin-receptor activation and the effect most associated with GHRP-6.
- Other pituitary hormones. Small rises in ACTH, cortisol and prolactin have been reported, as with the other early GHRPs. Ipamorelin was later called the first selective secretagogue because, in pig studies, it released GH without that response.
- Glucose control. Growth hormone opposes the action of insulin, so repeated GH elevation could affect blood glucose. This has not been studied properly for GHRP-6.
- Effects of raised GH. Fluid retention, joint pain and carpal tunnel symptoms are recognised effects of growth hormone treatment. Whether a secretagogue produces them depends on the size and duration of the GH rise, which is uncharacterised here.
- Material quality. There is no pharmaceutical-grade GHRP-6; identity and purity depend on the supplier and the certificate.
Regulatory status of GHRP-6 in Europe
GHRP-6 is not authorised as a medicine in the European Union, centrally or nationally, and it has no approved use elsewhere. Material sold in Europe is sold as a research chemical, not for human use; rules on possession and personal import differ between member states.
GHRP-6 is prohibited under S2 of the World Anti-Doping Agency Prohibited List, which covers peptide hormones, growth factors, related substances and mimetics and names the growth hormone releasing peptides. S2 substances are banned at all times, in and out of competition.
Sourcing GHRP-6 and checking quality
King Peptides does not stock GHRP-6. The closest product it carries is the CJC-1295 + Ipamorelin Blend 5/5 mg, which is not GHRP-6 in another form. Ipamorelin acts on the same ghrelin receptor but was selected for a narrower hormonal profile, while CJC-1295, a GHRH analogue, works through the other receptor on the somatotroph. The blend suits research on the combined GHRH and ghrelin-receptor response; it cannot stand in where GHRP-6 itself is the reference compound.
Whatever the source, check the certificate against the vial. HPLC purity should be at least 99%, the lot number on the document should match the label, and the mass should fit the compound: about 873 Da for GHRP-6, and for the blend a mass per component, 711.9 Da for ipamorelin and either 3647 Da with the DAC linker or 3368 Da without it, so check which form the product page states. King Peptides supplies a lot-specific certificate with HPLC and mass spectrometry and dispatches from the Netherlands; by the shop's own estimate delivery takes 1–2 business days within the Netherlands and 3–5 business days elsewhere in the EU, with no customs inside the EU. Our guides cover reading a certificate of analysis and storing lyophilised material at −20 °C.
GHRP-6: frequently asked questions
Is GHRP-6 the same as ghrelin? No. Ghrelin is a 28-amino-acid hormone made mainly in the stomach, and it needs an octanoyl fatty-acid group on its third amino acid to activate the receptor. GHRP-6 is a synthetic six-residue peptide that shares no sequence with it; the two meet only at GHS-R1a.
Why is GHRP-6 studied together with GHRH? The two act through different receptors and different intracellular signals, and together they release more GH than the sum of either alone. That combined effect is the basis of the GHRH plus GHRP-6 stimulation test.
Does the GH response fade with repeated dosing? A partial, reversible loss of response is documented in human studies of the closely related hexarelin, and desensitisation is a general property of the class. For GHRP-6 itself, human data on prolonged dosing are too thin to put a figure on it.
Where does GHRP-6 stand legally in Europe? It is not an authorised medicine and is sold only as research material; national rules decide what possession and import look like. For athletes the answer is simpler: prohibited at all times.
Research use only. GHRP-6 is described here for laboratory and scientific research. Research material carries no marketing authorisation, whatever the status of the molecule as a medicine elsewhere, and it is not intended for human or veterinary use. Nothing on this page is medical advice, and the dosing information above summarises published study designs. Always comply with the laws that apply in your country.