GHRP-1

What is GHRP-1?

GHRP-1 (Ala-His-D-β-Nal-Ala-Trp-D-Phe-Lys-NH2) is a synthetic growth hormone-releasing heptapeptide developed by Cyril Y. Bowers at Tulane University and Frank Momany at the U.S. Department of Agriculture in the late 1970s through systematic structural optimization of Met-enkephalin. Bowers had observed in the early 1970s that Met-enkephalin and its analogs unexpectedly stimulated growth hormone release in pituitary cell cultures — an effect not explained by classical opioid pharmacology. Working with Momany at USDA's Northern Regional Research Center (using protein-folding modeling that was unusually sophisticated for the time), Bowers and Momany systematically substituted residues to enhance GH-releasing activity while reducing opioid activity, eventually arriving at His-D-Trp-Ala-Trp-D-Phe-Lys-NH2 — initially called GHRP, later renamed GHRP-6. A subsequent series of analogs in the late 1970s and early 1980s produced a numbered set of growth hormone-releasing peptides, with GHRP-1 being one of the early members of the series. The 1981 Endocrinology paper by Momany, Bowers, and colleagues (PMID 6109621) is the foundational publication. GHRP-1 produces dose-dependent growth hormone release through what was later identified as the ghrelin receptor GHSR1a (Howard et al., Science 1996, PMID 10592437) — the molecular target that for years was an orphan receptor known only by its responsiveness to the GHRP class until the endogenous ligand ghrelin was identified by Kojima, Kangawa, and colleagues in 1999 (Nature, PMID 10604470). Although GHRP-1 was clinically tested in children and adolescents (Laron 1993, PMID 8279223) and was characterized for endocrine effects including thyroid pharmacology (Kraiem 1995, PMID 7627332), it was rapidly superseded in research and clinical interest by the more potent and better-characterized GHRP-2 and GHRP-6, and subsequently by hexarelin, ipamorelin, and the orally-active small-molecule GH secretagogue MK-677 (ibutamoren). GHRP-1 has no current therapeutic role and is not commonly available even in research-chemical channels; it is primarily a historical reference.

What GHRP-1 Is Investigated For

GHRP-1 is a historical and pharmacology-reference topic, not a contemporary research or consumer peptide. Its place in the timeline matters: GHRP-1 was one of the earliest numbered members of the synthetic growth hormone-releasing peptide series developed by Cyril Bowers at Tulane and Frank Momany at USDA in the late 1970s and early 1980s, derived from systematic structural optimization of Met-enkephalin. The 1981 Momany Endocrinology paper (PMID 6109621) reports the design, synthesis, and biological activity of the GHRP series including GHRP-1. Clinical experience with GHRP-1 was limited but real — Laron and colleagues at Tel Aviv University reported intranasal GHRP-1 administration in children and adolescents with clinically measurable plasma GH and IGF-1 increases (Acta Endocrinol 1993, PMID 8279223), and Hayashi at Showa University reported similar intranasal GH-releasing effects (Endocrinol Jpn 1991, PMID 1915110). Kraiem at Rambam Medical Center identified an unusual additional pharmacology: GHRP-1 (the heptapeptide) inhibited TSH-stimulated thyroid hormone secretion and cAMP formation in cultured human thyroid cells (Eur J Endocrinol 1995, PMID 7627332) — a thyroid effect not shared with GHRH and not extensively characterized in the subsequent GHRP class. The molecular target turned out to be the orphan G-protein-coupled receptor that Howard and colleagues at Merck cloned in 1996 as GHS-R (Science, PMID 10592437) and that Kojima, Kangawa, and colleagues deorphanized in 1999 as the receptor for ghrelin (Nature, PMID 10604470). The discovery program that began with GHRP-1 in the late 1970s thus eventually delivered one of the most important hormone systems in modern endocrinology — but GHRP-1 itself was rapidly outpaced by GHRP-2 (which became the workhorse research GH secretagogue), GHRP-6 (which has the most consumer-research-channel presence), hexarelin (more potent), ipamorelin (more selective for GH versus cortisol/prolactin), and MK-677/ibutamoren (orally active small molecule). GHRP-1 has no current FDA approval, no clinical use, and is not commonly stocked even by research-chemical peptide vendors. Anyone considering GH secretagogue therapy should engage with the validated and currently-available options — and recognize that the regulatory and scientific landscape favors GHRH analogs (sermorelin, tesamorelin) and selective ghrelin receptor agonists rather than the historical GHRP series.

History & Discovery

GHRP-1 emerged from the structural-optimization research program of Cyril Y. Bowers at Tulane University School of Medicine in New Orleans and Frank A. Momany at the U.S. Department of Agriculture's Northern Regional Research Center in Peoria, Illinois. Bowers had observed in the early 1970s, while studying GH-releasing factors at Tulane, that Met-enkephalin and its synthetic analogs unexpectedly stimulated growth hormone release in pituitary cell cultures — an effect not explained by classical opioid pharmacology and inconsistent with the prevailing view that opioids would inhibit rather than stimulate pituitary GH release. The observation pointed to a non-opioid pharmacology embedded in the Met-enkephalin scaffold, and Bowers initiated a structural-optimization program to enhance the GH-releasing activity while minimizing opioid-receptor binding. Momany joined the program in the mid-1970s, bringing protein-folding modeling capabilities that were unusually sophisticated for the time. Momany's structure-activity work — using empirical pharmacology and computational modeling in tandem — produced a series of peptide analogs of Met-enkephalin with progressively enhanced GH-releasing activity and reduced opioid activity. The synthetic GHRP that became GHRP-6 (His-D-Trp-Ala-Trp-D-Phe-Lys-NH2) was identified in 1980 and reported in the 1981 Momany Endocrinology paper (PMID 6109621). Subsequent analogs in the late 1970s and early 1980s produced the numbered GHRP series, with GHRP-1 (Ala-His-D-β-Nal-Ala-Trp-D-Phe-Lys-NH2) one of the early members of the family. Clinical interest in GHRP-1 developed through the 1980s and early 1990s. Hayashi at Showa University reported intranasal GHRP administration in 1991 (Endocrinol Jpn, PMID 1915110), demonstrating measurable plasma GH and IGF-1 elevations and establishing intranasal as a viable administration route for the class. Laron and colleagues at Tel Aviv University Sackler Faculty of Medicine reported a 1993 study of intranasal GHRP-1 specifically in children and adolescents with growth hormone deficiency, normal short children, and healthy controls (Acta Endocrinol Copenh, PMID 8279223), with measurable GH and IGF-1 elevations across all groups. Kraiem and colleagues at Rambam Medical Center in Haifa identified an unusual additional pharmacology in 1995 (Eur J Endocrinol, PMID 7627332): GHRP-1 inhibited TSH-stimulated thyroid hormone secretion and cAMP formation in cultured human thyroid cells — a thyroid effect not shared with GHRH and not extensively characterized in subsequent GHRP-class research. The broader scientific significance of the GHRP discovery program emerged in the mid-to-late 1990s. Howard, Feighner, and colleagues at Merck Research Laboratories cloned the orphan receptor responsible for GHRP signaling in 1996 (Science, PMID 10592437), naming it the growth hormone secretagogue receptor (GHS-R, now GHSR1a). The receptor was identified specifically by its responsiveness to the GHRP class — the synthetic GHRPs developed by Bowers and Momany were the molecular bait that led to receptor identification. Three years later, in 1999, Kojima, Kangawa, Hosoda, and Matsuo at the National Cardiovascular Center in Osaka identified the endogenous ligand of GHSR1a (Nature, PMID 10604470) as ghrelin — a 28-amino-acid peptide produced by gastric X/A-like cells with a unique octanoyl modification on serine-3. The discovery of ghrelin and the elaboration of its physiological roles in growth hormone regulation, appetite, gastric motility, glucose metabolism, and reproductive biology has had downstream consequences across modern endocrinology — and GHRP-1 was an early piece of the pharmacology that led to it. GHRP-1 itself was rapidly overtaken in research and clinical interest by the more potent and better-characterized members of the GHRP series. GHRP-2 (D-Ala-D-β-Nal-Ala-Trp-D-Phe-Lys-NH2) became the workhorse research GH secretagogue and was developed clinically through phase 2 trials before commercial discontinuation. GHRP-6 (the original prototype) acquired the most consumer-research-channel availability. Hexarelin (His-D-2-Me-Trp-Ala-Trp-D-Phe-Lys-NH2) became a more potent option used in research. Ipamorelin (Aib-His-D-β-Nal-D-Phe-Lys-NH2) became the GHRP-class member most distinguished by selectivity for GH release without significant cortisol or prolactin elevation. The orally-active small-molecule GH secretagogue MK-677 (ibutamoren), developed at Merck through 1990s small-molecule optimization following the GHSR1a cloning, became the dominant ghrelin receptor agonist in research and consumer-research-channel use. GHRP-1 has no FDA approval, no current clinical use, and is not commonly available — it is primarily a historical reference and a footnote in the discovery story of the ghrelin/GHSR signaling system.

How It Works

GHRP-1 is one of the earliest synthetic growth hormone-boosting peptides ever made — designed in the late 1970s and early 1980s by researchers at Tulane and the USDA who started with Met-enkephalin (a small natural opioid peptide) and tweaked its structure until they got something that strongly stimulated growth hormone release without much opioid activity. GHRP-1 works by binding the ghrelin receptor (GHSR1a) on pituitary cells, which then release growth hormone. The discovery of GHRP-1 and its siblings (GHRP-2, GHRP-6, hexarelin, ipamorelin) eventually led scientists to discover ghrelin itself in 1999 — one of the most important hormone discoveries of the past 30 years. GHRP-1 was rapidly outclassed by its newer siblings and is mostly a historical reference today.

GHRP-1 (Ala-His-D-β-Nal-Ala-Trp-D-Phe-Lys-NH2) is a synthetic heptapeptide structurally derived from systematic optimization of Met-enkephalin. Bowers and Momany's design strategy in the late 1970s was driven by the observation that Met-enkephalin and analogs produced GH-releasing activity in pituitary cell cultures, and the optimization aim was to enhance GH-releasing potency while reducing opioid receptor binding. The series produced GHRP-1 (an early numbered member), GHRP-2 (the most-used research GH secretagogue, sequence D-Ala-D-β-Nal-Ala-Trp-D-Phe-Lys-NH2), GHRP-6 (sequence His-D-Trp-Ala-Trp-D-Phe-Lys-NH2), and hexarelin (sequence His-D-2-Me-Trp-Ala-Trp-D-Phe-Lys-NH2). All share a small (6-7 residue) peptide backbone with C-terminal lysinamide and the central Trp-D-Phe pharmacophore that drives ghrelin-receptor binding. GHRP-1 acts at the growth hormone secretagogue receptor (GHSR1a, also known as the ghrelin receptor), a class A G-protein-coupled receptor encoded by the GHSR gene on human chromosome 3q26.31. GHSR1a was cloned and characterized as an orphan receptor in 1996 by Howard, Feighner, and colleagues at Merck Research Laboratories (Science, PMID 10592437), identified specifically by its responsiveness to the synthetic GHRP class — the GHRPs were the molecular bait that led to receptor identification. The endogenous ligand of GHSR1a was identified three years later in 1999 by Kojima, Kangawa, Hosoda, and Matsuo at the National Cardiovascular Center in Osaka (Nature, PMID 10604470) as ghrelin, a 28-amino-acid peptide produced by gastric X/A-like cells with a unique octanoyl modification on serine-3. The receptor couples primarily to Gq/11 with phospholipase C activation and intracellular calcium mobilization, and to Gs/cAMP secondarily, producing growth hormone release in pituitary somatotrophs. GHRP-1 (like other GHRPs) drives this signaling and produces dose-dependent GH release in vivo. The pharmacology of GHRP-1 includes the standard GH secretagogue effects: pituitary GH release with downstream IGF-1 elevation, modest cortisol and prolactin elevations through pituitary GHSR1a expression, and central effects on appetite and gastric motility through hypothalamic and brainstem GHSR1a. Kraiem's 1995 Eur J Endocrinol paper (PMID 7627332) identified an unusual additional pharmacology specific to GHRP-1: inhibition of TSH-stimulated thyroid hormone secretion and cAMP formation in cultured human thyroid cells, suggesting a peripheral GHSR1a-independent action not shared with GHRH or with subsequent GHRP class members. This thyroid effect has not been extensively characterized in modern research. The administration profile of GHRP-1 in the historical literature was predominantly intranasal (Hayashi 1991 PMID 1915110; Laron 1993 PMID 8279223), which produced measurable plasma GH and IGF-1 elevations in healthy and growth-hormone-deficient subjects without requiring injection. The intranasal route reflected the formulation and bioavailability characteristics of GHRP-1 at the time and is broadly consistent with the GH secretagogue class, members of which have been developed for various administration routes (subcutaneous and IV for GHRP-2 and hexarelin; oral for MK-677/ibutamoren; intranasal explored for several). GHRP-1 is now of mainly historical interest. Its place in the timeline matters as part of the foundational pharmacology that led to the ghrelin receptor and ghrelin itself, but its potency is lower than GHRP-2 and hexarelin, its receptor selectivity is similar to other GHRPs (no special advantage over ipamorelin's GH-selective profile), and it does not have an oral formulation comparable to MK-677. Modern GH secretagogue research and clinical interest is focused on the validated and currently-available molecules.

Evidence Snapshot

Research Gaps & Open Questions

What the current literature has not yet settled about GHRP-1:

• 01Whether GHRP-1's distinctive thyroid pharmacology (inhibition of TSH-stimulated thyroid hormone secretion, identified by Kraiem 1995) is mechanistically discrete from other GHRP class members and clinically meaningful — not characterized in modern research.
• 02Whether GHRP-1 has any specific advantage over the better-characterized members of the GHRP series (GHRP-2, ipamorelin, hexarelin, MK-677) — the lack of a clear advantage is the principal reason GHRP-1 was not advanced into clinical development.
• 03What the long-term safety profile of any GHRP-class agent (including GHRP-1) is in chronic dosing — modern long-term safety data for the class is limited even for the more-studied members (MK-677, ipamorelin).
• 04Whether the GH secretagogue class will eventually find a clinical indication beyond the few niche uses (cachexia, post-operative ileus, diagnostic GH stimulation testing) where it has been characterized, given the dominance of recombinant GH (somatropin) and GHRH analogs (sermorelin, tesamorelin) in current clinical practice.

Forms & Administration

GHRP-1 is not formulated or approved as a therapeutic in any jurisdiction. The historical clinical literature predominantly used intranasal administration in single-dose pharmacology studies. There is no current FDA-approved pen, vial, or formulation, and the molecule is not commonly available even in research-chemical peptide vendor catalogs that stock GHRP-2, GHRP-6, hexarelin, and ipamorelin. Anyone seeking growth hormone secretagogue therapy should engage with currently-available options under medical supervision: GHRH analogs (sermorelin, tesamorelin) for medical indications, the ghrelin receptor agonists ipamorelin (research-channel) or MK-677/ibutamoren (research-channel small molecule), or recombinant human growth hormone (somatropin) for medically-validated indications.

Common Questions

Who GHRP-1 Is NOT For

Drug & Supplement Interactions

There is no validated human drug-interaction profile for GHRP-1 because no clinical product is in current use. Theoretical interactions extrapolate from the GH secretagogue class. Concurrent use with other GH secretagogues (GHRP-2, GHRP-6, hexarelin, ipamorelin, MK-677), GHRH analogs (sermorelin, tesamorelin), or somatropin would produce additive GH and IGF-1 elevations with theoretical concerns about insulin resistance, fluid retention, and edema. Concurrent use with corticosteroids would compound cortisol elevation and could exacerbate hypercortisolism. Concurrent use with insulin or insulin secretagogues in diabetic patients could worsen insulin resistance. The unusual thyroid pharmacology identified by Kraiem 1995 (inhibition of TSH-stimulated thyroid hormone secretion) raises a theoretical concern in patients on thyroid hormone replacement, though the clinical relevance is unknown. None of these interactions has been characterized in controlled human studies for GHRP-1.

Safety Profile

Legal Status

Regulatory status changes over time. Verify current local rules with a qualified professional.

Myths & Misconceptions