In Plain English:
GHRP-2 (pralmorelin) is a synthetic six-amino-acid peptide that mimics ghrelin, the body's own hunger and growth hormone trigger. It binds the ghrelin receptor (GHS-R1a) in the pituitary gland, firing a rapid and potent GH pulse within 15–30 minutes of injection — the strongest GH output of any natural hexapeptide secretagogue. Unlike its cousin GHRP-6, it produces significantly less appetite stimulation, sitting in a middle ground: cleaner than GHRP-6, slightly more hormonal side effects than ipamorelin. In 2004 it became the only growth hormone secretagogue ever approved by a regulatory body, cleared by Japan's PMDA under the brand Pralmorelin Kaken as a single-dose diagnostic test for GH deficiency in adults and children. It is not approved for human therapeutic use anywhere and remains a research compound outside Japan.
Research Maturity
Limited Human (255 PubMed publications (1984–2026); human data limited to small acute trials (N≤10)+ Studies)
Focus
Body Composition
Growth Hormone Axis
Metabolic Signaling
Origin
Synthetic hexapeptide developed as a potent analogue of GHRP-6 by Kaken Pharmaceutical in Japan (internal code KP-102). Structurally derived from met-enkephalin analogues incorporating D-amino acids (D-Ala, D-β-naphthylalanine, D-Phe) for protease resistance and receptor selectivity. First characterised in the 1980s as part of Cyril Bowers' series of growth hormone secretagogues; developed through Phase II trials by Kaken and Wyeth-Ayerst in the 1990s-2000s. Japanese PMDA approval granted October 2004 for diagnostic GH stimulation testing — the first and still only regulatory approval for any growth hormone secretagogue worldwide.
Mechanism
Full agonist at GHS-R1a (growth hormone secretagogue receptor type 1a), a Gq-coupled GPCR expressed on anterior pituitary somatotroph cells and hypothalamic arcuate nucleus neurons. Binding activates phospholipase C → IP3/DAG cascade → intracellular Ca²⁺ mobilisation → pulsatile GH secretion. Simultaneously suppresses somatostatin tone in the hypothalamus and amplifies endogenous GHRH signalling, producing a synergistic GH pulse 3–10× greater than GHRH alone when co-administered. Receptor is partially non-selective: corticotroph cell GHS-R1a activation drives ACTH/cortisol co-secretion, and lactotroph activation causes mild prolactin elevation — effects absent with selective agents like ipamorelin. At the pituitary, GH release saturates at approximately 1 mcg/kg IV; higher doses produce proportionally greater ACTH/cortisol without additional GH benefit.
Outcome
Peak serum GH (Cmax ~50 ng/mL at diagnostic IV dosing; Tmax ~25 min), GH area under curve, serum IGF-1, ACTH/cortisol co-secretion, prolactin, food intake/caloric intake, body weight (cachexia/anorexia nervosa models), GH pulse amplitude and frequency.
