GHRP-2 (Pralmorelin): Growth Hormone Secretagogue Peptide Monograph

Overview: what GHRP-2 is

GHRP-2, also called pralmorelin and by the development code KP-102, is a synthetic hexapeptide with the sequence D-Ala-D-2-Nal-Ala-Trp-D-Phe-Lys-NH2. It belongs to the growth hormone releasing peptide (GHRP) family, a group of small peptides that grew out of a synthetic hexapeptide shown by Cyril Bowers and colleagues in the 1980s to release growth hormone directly at the pituitary ^[1]. GHRP-2 is one of the more potent members of that family and is studied as a growth hormone secretagogue, meaning a molecule that prompts the pituitary to release its own growth hormone (GH) rather than supplying GH from outside.

This monograph is a scientific reference for research use only. It reports what the published literature says, separates animal and cell data from genuine human data, and gives no dosing guidance and no instructions for administration to people.

Structure and physicochemistry

GHRP-2 is a six-residue peptide amide built partly from D-amino acids and containing an unnatural 2-naphthylalanine residue. Those features slow enzymatic breakdown relative to native peptides. The free base has the molecular formula C45H55N9O6 and a molar mass of about 818 g/mol; the CAS (Chemical Abstracts Service number) number for the free base is 158861-67-7. Research material is usually supplied as a lyophilized (freeze-dried) powder, often as an acetate salt. Everything stated here concerns the physicochemical properties of the substance under laboratory conditions and is not preparation or dosing guidance.

Mechanism of action

GHRP-2 does not act on the growth hormone releasing hormone (GHRH) receptor. It binds the growth hormone secretagogue receptor type 1a (GHS-R1a), a G-protein-coupled receptor identified in the pituitary and hypothalamus in 1996 ^[2]. For several years this receptor was an orphan, meaning its natural ligand was unknown, until ghrelin, an acylated peptide from the stomach, was described as the endogenous agonist in 1999 ^[3]. GHRP-2 is therefore a synthetic ghrelin-receptor agonist that predates the discovery of ghrelin itself.

Activation of GHS-R1a couples to Gq/11, phospholipase C, and the inositol trisphosphate pathway, raising intracellular calcium in pituitary somatotrophs and promoting release of stored GH ^[4]. The peptide is thought to act at two levels: directly on the somatotrophs and on the hypothalamus, where it can increase GHRH release and blunt somatostatin, the natural brake on GH. This dual action, reviewed in detail for the GHRP class, is part of why GHRPs can produce GH responses larger than GHRH alone and can act synergistically with GHRH ^[5][6].

Research evidence: preclinical versus human

Preclinical (animal and in vitro). The founding pharmacology of this peptide class was established in cell cultures and animals, where the parent hexapeptide released GH specifically at the pituitary ^[1]. For GHRP-2 itself, chronic administration was tested in the GHRH-knockout mouse, a model with disrupted GHRH signaling; long-term GHRP-2 raised GH and IGF-1 and supported growth, evidence that the peptide can drive the GH axis even when GHRH signaling is impaired, while also noting that these are animal endpoints ^[11]. Animal data serve as mechanistic support, not clinical outcomes, and cross-species differences complicate extrapolation to humans.

Human data (reported as literature facts). GHRP-2 has genuinely been studied in people, which sets it apart from many research peptides. In healthy men, single doses produced a marked, dose-related rise in GH that exceeded the response to a maximal dose of GHRH, along with smaller increases in prolactin, ACTH, and cortisol ^[7]. In a separate controlled study in healthy men, an infusion of GHRP-2 increased food intake, mirroring the appetite effect of ghrelin and confirming that the compound engages ghrelin-receptor biology beyond GH release ^[10]. In children of short stature, intranasal GHRP-2 reliably raised GH and was associated with increased growth velocity over several months in an early open study ^[8], and eight months of graded subcutaneous GHRP-2 in GH-deficient children increased overnight GH secretion and growth velocity during treatment ^[9].

The honest counterpoint comes from a later, larger, placebo-controlled trial: in prepubertal children with GH deficiency, an intranasal GHRP-2 spray increased endogenous GH secretion but produced no meaningful growth over 48 weeks compared with placebo, the authors reasoning that the GH exposure achieved was too small to translate into growth ^[12]. Taken together, the human literature shows that GHRP-2 does what its mechanism predicts, releasing GH and stimulating appetite acutely, but does not establish it as an effective treatment for any growth or body-composition indication.

Regulatory context. The clearest real-world use of GHRP-2 is diagnostic. In Japan, pralmorelin is approved as a single-injection provocative agent to test the pituitary's capacity to release GH when GH deficiency is suspected. That is a diagnostic approval, not approval as a therapy, and no jurisdiction has approved GHRP-2 as a treatment.

Pharmacokinetics and metabolism

GHRP-2 is a short-acting peptide: after parenteral dosing the GH response is rapid and transient, consistent with a plasma half-life on the order of tens of minutes. Analytical work in humans has characterized how the intact peptide and a specific metabolite (designated AA-3) appear in urine after intravenous dosing, which matters both for metabolism and for anti-doping detection, since GHRP-2 is a prohibited substance in sport ^[13].

Safety and handling (research context)

Reported acute effects in human studies are usually mild and reflect the receptor pharmacology: transient rises in prolactin, ACTH, and cortisol accompany the GH response, and GHRP-2 tends to raise cortisol and prolactin somewhat more than some other GHRPs ^[7]. Appetite stimulation is expected from ghrelin-receptor agonism ^[10]. Long-term safety in humans is not established, because the compound has never completed the trials a therapeutic approval would require. Laboratory handling of the lyophilized peptide follows standard practice for such material: cold storage, protection from moisture and light, and reconstitution only for in vitro or animal work. None of this is guidance for use in people.

Research status and disclaimer

GHRP-2 remains a tool for studying the ghrelin, GHS-R1a, GH, and IGF-1 axis and, in one jurisdiction, a diagnostic agent. It has no approved therapeutic indication anywhere. This page is a neutral summary of the scientific literature, provided strictly for research purposes, with no dosing recommendations and no suggestion of human use. Regimen tables, where they exist elsewhere on this site, are separate reference material and are likewise not medical advice.