Ghrelin vs GHRP-6

GHRP-6 was discovered before ghrelin itself and acts on the same receptor, GHS-R1a. Ghrelin is the native, acylated 28-amino-acid hormone; GHRP-6 is a small synthetic peptide that mimics its GH-releasing and appetite effects.

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Ghrelin

The endogenous 28-amino-acid stomach hormone that activates the growth-hormone secretagogue receptor — the natural ligand every synthetic secretagogue imitates.

BEST STUDIED FOR

GH secretagogues

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GHRP-6

One of the first synthetic growth-hormone-releasing hexapeptides, a ghrelin-receptor agonist studied for GH release and as a diagnostic probe.

BEST STUDIED FOR

GH secretagogues

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SIDE BY SIDE

	Ghrelin	GHRP-6
The key difference	Endogenous hormone	Synthetic hexapeptide agonist
Class	GH secretagogues	GH secretagogues
Mechanism	Discovered in 1999 as the natural ligand of GHS-R1a, acylated ghrelin stimulates pituitary GH release and is a powerful orexigenic (appetite) signal.	GHRP-6 binds the ghrelin receptor (GHS-R1a) and stimulates pituitary GH release; it was used to characterise that receptor before ghrelin itself was discovered.
Status	Endogenous hormone and research tool; synthetic ghrelin-receptor agonists (anamorelin, macimorelin) have reached approval in specific indications elsewhere.	A research and diagnostic tool from the 1990s onward; not an approved medicine. Banned in sport.
Reported safety signals	As a research reagent it is a physiological hormone; increased appetite and GH/cortisol release are expected pharmacology.	Older diagnostic studies used single doses. Class-wide, GHRPs raise cortisol/prolactin and increase hunger; there are no long-term human safety data.
A key study	The discovery paper identifying ghrelin as the endogenous, acylated ligand of the GH secretagogue receptor. (Nature 1999, PMID 10604470)	Assessed GHRP-6 as a provocative test of pituitary GH reserve in the diagnosis of GH deficiency. (J Pediatr Endocrinol Metab 1996, PMID 8887178)

WHEN TO RESEARCH WHICH

Ghrelin for endocrine physiology; GHRP-6 for a stable, synthetic probe of the same receptor. Both are discussed here strictly as research compounds; nothing on this page is medical advice or a dosing guide.

REFERENCES (PUBMED)

[Ghrelin] Ghrelin is a growth-hormone-releasing acylated peptide from stomach — Nature 1999. PMID 10604470
[Ghrelin] Ghrelin — Mol Metab 2015. PMID 26042199
[Ghrelin] Ghrelin and Neurodegenerative Disorders-a Review — Mol Neurobiol 2017. PMID 26809582
[GHRP-6] Growth hormone releasing hexapeptide-6 (GHRP-6) test in the diagnosis of GH-deficiency — J Pediatr Endocrinol Metab 1996. PMID 8887178
[GHRP-6] Growth hormone-releasing peptides and their analogs — Front Neuroendocrinol 1998. PMID 9465289
[GHRP-6] Beyond the androgen receptor: the role of growth hormone secretagogues in the modern management of body composition in hypogonadal males — Transl Androl Urol 2020. PMID 32257855

FREQUENTLY ASKED

What is the difference between Ghrelin and GHRP-6?

What is the regulatory status of Ghrelin and GHRP-6?

Ghrelin: Endogenous hormone and research tool; synthetic ghrelin-receptor agonists (anamorelin, macimorelin) have reached approval in specific indications elsewhere. GHRP-6: A research and diagnostic tool from the 1990s onward; not an approved medicine. Banned in sport.

What safety signals have been reported?

Ghrelin: As a research reagent it is a physiological hormone; increased appetite and GH/cortisol release are expected pharmacology. GHRP-6: Older diagnostic studies used single doses. Class-wide, GHRPs raise cortisol/prolactin and increase hunger; there are no long-term human safety data.

Which studies is this comparison based on?

For Ghrelin: “Ghrelin is a growth-hormone-releasing acylated peptide from stomach” (PMID 10604470); “Ghrelin” (PMID 26042199); “Ghrelin and Neurodegenerative Disorders-a Review” (PMID 26809582). For GHRP-6: “Growth hormone releasing hexapeptide-6 (GHRP-6) test in the diagnosis of GH-deficiency” (PMID 8887178); “Growth hormone-releasing peptides and their analogs” (PMID 9465289); “Beyond the androgen receptor: the role of growth hormone secretagogues in the modern management of body composition in hypogonadal males” (PMID 32257855).