GHRP-2: Complete Research Guide & Chemical Profile

GHRP-2 (Growth Hormone Releasing Peptide-2), also known by its INN pralmorelin, is a synthetic hexapeptide growth hormone secretagogue that activates the growth hormone secretagogue receptor type 1a (GHS-R1a). Developed by Cyril Y. Bowers through structure-activity relationship optimization of the original GHRP-6 scaffold, GHRP-2 is considered the most potent member of the classical hexapeptide growth hormone secretagogue family on a molar basis.

• Generic Name: GHRP-2 (Pralmorelin)
• INN: Pralmorelin
• CAS Registry Number: 158861-67-7
• Molecular Formula: C₄₅H₅₅N₉O₆
• Molecular Weight: 817.97 Da
• Amino Acid Sequence: D-Ala-D-2Nal-Ala-Trp-D-Phe-Lys-NH₂
• Peptide Length: 6 amino acid residues (hexapeptide)
• Classification: Synthetic growth hormone secretagogue, GHS-R1a agonist
• Regulatory Status: Approved in Japan as diagnostic agent for GH deficiency (PMDA, 2004)

GHRP-2 is a linear hexapeptide with the sequence D-Ala-D-2Nal-Ala-Trp-D-Phe-Lys-NH₂. The key structural distinction from GHRP-6 is the substitution of D-2-naphthylalanine (D-2Nal, also written as D-beta-Nal) at position 2, replacing the D-tryptophan found in GHRP-6. This single amino acid change substantially enhances GH-releasing potency while modifying the selectivity profile. Additionally, position 1 uses D-alanine instead of histidine.

The D-2-naphthylalanine residue features a bicyclic naphthalene ring system that provides an extended aromatic surface for hydrophobic interactions within the GHS-R1a binding pocket. This larger aromatic surface area compared to the single indole ring of D-tryptophan in GHRP-6 results in enhanced receptor binding affinity and increased potency. Like GHRP-6, the C-terminus is amidated (-NH₂) for metabolic stability.

• Position 1 — D-Ala (D-Alanine): Small hydrophobic D-amino acid; differs from His in GHRP-6. Provides DPP-4 resistance at the N-terminus.
• Position 2 — D-2Nal (D-2-Naphthylalanine): Critical modification. The bicyclic naphthalene ring enhances hydrophobic interactions in the GHSR-1a binding pocket. This substitution is the primary driver of GHRP-2's enhanced potency over GHRP-6.
• Position 3 — Ala (L-Alanine): Hydrophobic spacer residue, same as GHRP-6
• Position 4 — Trp (L-Tryptophan): Aromatic residue essential for receptor activation, same as GHRP-6
• Position 5 — D-Phe (D-Phenylalanine): D-amino acid that engages the hydrophobic binding pocket, same as GHRP-6
• Position 6 — Lys (L-Lysine): Positively charged residue with C-terminal amidation (-NH₂), same as GHRP-6

GHRP-2 activates the GHS-R1a receptor through the same Gq/11-coupled signaling mechanism as GHRP-6 and endogenous ghrelin. Upon binding, the receptor activates phospholipase C (PLC), generating inositol trisphosphate (IP₃) and diacylglycerol (DAG). IP₃ triggers calcium release from intracellular stores, and the resulting calcium elevation drives growth hormone vesicle exocytosis from anterior pituitary somatotrophs.

The enhanced binding affinity of GHRP-2 compared to GHRP-6 translates to greater GH release per unit dose. However, GHRP-2 also stimulates ACTH, cortisol, and prolactin secretion, placing its selectivity profile between GHRP-6 (moderate non-selectivity) and hexarelin (highest non-selectivity). The relative stimulation of these secondary hormones is dose-dependent and more pronounced at higher concentrations.

• Primary Target: GHS-R1a (ghrelin receptor) — Gq/11-coupled GPCR
• GH Release Potency: Most potent of the classical hexapeptide GHRPs per unit dose
• ACTH/Cortisol Stimulation: Present but less than hexarelin; more than ipamorelin
• Prolactin Stimulation: Mild elevation at standard research concentrations
• Appetite Stimulation: Less pronounced than GHRP-6, likely due to the D-Ala/D-2Nal substitutions affecting hypothalamic receptor engagement

GHRP-2 occupies a specific position in the selectivity spectrum of growth hormone secretagogues. It produces the strongest GH release of the classical hexapeptide GHRPs on a molar basis, while its effects on secondary hormones (ACTH, cortisol, prolactin) are intermediate between GHRP-6 and hexarelin.

• GH Selectivity Ranking (most to least selective): Ipamorelin > GHRP-6 > GHRP-2 > Hexarelin
• GH Potency Ranking (most to least potent): Hexarelin > GHRP-2 > GHRP-6 > Ipamorelin
• Appetite Stimulation Ranking (most to least): GHRP-6 > GHRP-2 > Hexarelin > Ipamorelin
• ACTH/Cortisol Stimulation: GHRP-2 stimulates approximately 2-3x less ACTH/cortisol than hexarelin but more than ipamorelin (which produces negligible ACTH/cortisol stimulation)

This intermediate selectivity profile makes GHRP-2 a versatile research tool. It is potent enough to produce robust GH responses while its moderate effects on secondary hormones provide a useful window for studying multi-hormone pituitary release patterns without the overwhelming non-selectivity of hexarelin.

GHRP-2 is widely used in endocrinology research and has the distinction of being the only growth hormone secretagogue with any form of regulatory approval worldwide. Key research areas include:

• GH Deficiency Diagnostics: GHRP-2 (pralmorelin) is approved in Japan as a provocative test agent for the diagnosis of growth hormone deficiency. The GHRP-2 stimulation test offers advantages over insulin tolerance testing (ITT) due to its superior safety profile and reproducibility.
• Pituitary Function Testing: Investigating somatotroph reserve capacity and the integrity of the GHS-R1a signaling pathway in various hypothalamic-pituitary conditions.
• GH Secretagogue Pharmacology: Comparative studies of GH secretagogue potency, selectivity, and structure-activity relationships using GHRP-2 as a high-potency reference compound.
• Aging and GH Axis: Studying age-related changes in GHS-R1a receptor density, signaling efficiency, and GH pulse amplitude using GHRP-2 as a standardized stimulus.
• Sleep and Circadian Biology: Investigating the effects of GHS-R1a activation on sleep architecture, slow-wave sleep, and circadian GH secretion patterns.
• Immune Modulation: Exploring GH-axis stimulation effects on immune cell function, thymic involution, and inflammatory responses in preclinical models.

GHRP-2 shares the rapid pharmacokinetic profile characteristic of unmodified hexapeptide secretagogues. Its short half-life and fast onset make it well-suited for acute GH stimulation studies and diagnostic applications but limit sustained GH elevation.

• Half-life: Approximately 20-30 minutes
• Onset of Action: GH elevation detectable within 5-15 minutes after administration
• Peak GH Response: 30-60 minutes post-administration (slightly delayed vs. GHRP-6)
• Duration of GH Elevation: Approximately 3-4 hours
• Metabolism: Rapid proteolytic degradation by serum peptidases; the D-amino acids at positions 1, 2, and 5 provide moderate protection against aminopeptidases
• Bioavailability: Subcutaneous ~50-65%; intranasal delivery has been investigated with moderate bioavailability; oral bioavailability negligible

Understanding the structural and pharmacological differences between GHRP-2 and related secretagogues is essential for selecting the optimal research tool.

• GHRP-2 vs. GHRP-6: GHRP-2 is more potent (stronger GH release per dose), has less appetite stimulation, and shows slightly more ACTH/cortisol co-stimulation. Key structural difference: D-2Nal (GHRP-2) vs. D-Trp (GHRP-6) at position 2, and D-Ala (GHRP-2) vs. His (GHRP-6) at position 1. GHRP-2 MW: 817.97 Da vs. GHRP-6 MW: 873.01 Da.
• GHRP-2 vs. Ipamorelin: Ipamorelin is pentapeptide (5 residues) with near-perfect GH selectivity — no significant ACTH, cortisol, or prolactin stimulation. GHRP-2 is more potent for total GH release but less selective. Choose GHRP-2 for maximum GH output; ipamorelin for clean GH-only signaling.
• GHRP-2 vs. Hexarelin: Hexarelin is the most potent hexapeptide GHRP overall but is the least selective — strongest ACTH/cortisol/prolactin co-stimulation. GHRP-2 offers a better selectivity-to-potency ratio for most research applications.
• GHRP-2 vs. CJC-1295: CJC-1295 is a GHRH analogue (not a GHRP). It activates the Gs/cAMP pathway rather than the Gq/Ca²⁺ pathway. GHRP-2 and CJC-1295 produce synergistic GH release when combined due to complementary signaling mechanisms.

GHRP-2 is a stable hexapeptide with storage requirements similar to GHRP-6. The D-2-naphthylalanine residue introduces a unique consideration — the extended aromatic system is somewhat more susceptible to photo-oxidation than standard amino acids.

• Lyophilized Powder: Store at -20°C. Stable for 36+ months when dry and sealed under inert gas. Short-term storage at 2-8°C acceptable for weeks.
• Reconstituted Solution: Store at 2-8°C. Use within 21-28 days in bacteriostatic water; 7-14 days in sterile water.
• Reconstitution Vehicle: Bacteriostatic water (0.9% benzyl alcohol) for multi-use; sterile water for single-use preparations.
• Light Protection: Store in amber vials. The Trp residue (position 4) and D-2Nal residue (position 2) are both aromatic and susceptible to UV-induced oxidation.
• pH Stability: Stable across pH 3.0-7.0. Optimal at pH 4.0-5.5.
• Solubility: Freely soluble in water (>10 mg/mL). Also soluble in DMSO, methanol, and dilute acetic acid.

Analytical characterization of GHRP-2 follows standard hexapeptide protocols with special attention to the non-coded D-2-naphthylalanine residue. The slightly lower molecular weight compared to GHRP-6 (817.97 vs. 873.01 Da) requires accurate mass determination for identification.

• RP-HPLC (C18 Column): Standard C18 column, 100-120 Å pore size. Gradient: 10-60% acetonitrile/water with 0.1% TFA over 20 minutes. UV detection at 220 nm and 280 nm. The D-2Nal residue provides strong UV absorbance at 280 nm. Purity threshold: ≥95% for research grade.
• Mass Spectrometry: ESI-MS or MALDI-TOF to confirm MW of 817.97 Da. Expected [M+H]⁺ = 818.98. Compare against GHRP-6 [M+H]⁺ = 874.02 to distinguish the two peptides.
• Amino Acid Analysis: Should show Ala:Trp:Phe:Lys in expected ratios. D-2Nal is a non-coded amino acid that will NOT appear in standard AAA databases — its presence must be confirmed by MS or NMR.
• Chiral Amino Acid Analysis: Marfey's method to confirm D-configuration at positions 1 (D-Ala), 2 (D-2Nal), and 5 (D-Phe). Three of six residues are D-amino acids — enantiomeric purity is critical for biological activity.
• MS/MS Sequencing: Collision-induced dissociation (CID) of the intact peptide. The D-2Nal residue produces a characteristic immonium ion at m/z 170.1 that serves as a diagnostic fingerprint.
• CoA Requirements: HPLC chromatogram, MS spectrum, net peptide content, appearance, and solubility data. Chiral analysis results are highly recommended.

GHRP-2 (pralmorelin) holds the unique distinction of being the only growth hormone secretagogue to receive regulatory approval for clinical use. In October 2004, pralmorelin was approved by the Japanese Pharmaceuticals and Medical Devices Agency (PMDA) as a diagnostic agent for growth hormone deficiency assessment in both adults and children. This approval was based on clinical data demonstrating that the GHRP-2 stimulation test provides reliable assessment of somatotroph function with a favorable safety profile compared to the insulin tolerance test.

Beyond the approved diagnostic indication, GHRP-2 has been investigated in Phase 2 clinical trials for short stature assessment and continues to be actively researched for effects on sleep architecture, immune function, appetite regulation, and aging-related GH decline. In research settings, GHRP-2 remains a preferred tool compound when maximum GH-releasing potency from a hexapeptide secretagogue is required, while researchers seeking clean GH selectivity typically opt for ipamorelin. The peptide's well-characterized pharmacological profile, combined with its regulatory precedent in Japan, makes it one of the most thoroughly documented growth hormone secretagogues available for laboratory research.

Explore detailed chemical profiles and research guides for compounds discussed in this article:

• GHRP-6: Complete Research Guide → /learn/ghrp-6-research-guide-chemical-profile

• Read more: Ipamorelin + CJC-1295 (No DAC) Stack: Synergy Research Guide → https://www.chemverify.com/learn/ipamorelin-cjc-1295-no-dac-stack-synergy
• Read more: Peptide Cycling: How Long to Research and When to Pause → https://www.chemverify.com/learn/peptide-cycling-research-duration-pause
• Read more: Growth Hormone Secretagogues Explained: How Ipamorelin, CJC-1295 and GHRP-6 Work → https://www.chemverify.com/learn/growth-hormone-secretagogues-explained-ipamorelin-cjc1295
• Read more: Semax for Cognitive Research: ACTH(4-10) Analog Mechanism → https://www.chemverify.com/learn/semax-cognitive-research-acth-mechanism