GHRP-2

Overview

GHRP-2 (Growth Hormone Releasing Peptide-2), also known by its research designations KP-102 and Pralmorelin, is a synthetic hexapeptide growth hormone secretagogue developed in the early 1990s. It is considered the most potent GHRP on a per-milligram basis, producing greater peak GH release than GHRP-6, Ipamorelin, or Hexarelin at equivalent doses.

GHRP-2 occupies an intermediate position in the GHRP selectivity spectrum. It produces significantly less appetite stimulation than GHRP-6, making it more practical for research subjects who do not desire increased hunger. However, it produces more pronounced cortisol and prolactin elevation than Ipamorelin, though less than Hexarelin. This intermediate profile has made GHRP-2 a common choice in research protocols where maximal GH output is prioritized.

In Japan, GHRP-2 (as Pralmorelin) received regulatory approval for diagnostic use — specifically as a provocative agent for testing GH secretory capacity in suspected GH deficiency. This represents one of the few regulatory approvals for any GHRP compound, though it is approved for single-dose diagnostic administration rather than therapeutic use.

GHRP-2 was extensively studied by Cyril Bowers and other endocrinology researchers throughout the 1990s and 2000s, contributing significantly to the understanding of the ghrelin/GHS-R1a signaling axis.

Amino Acid Sequence

GHRP-2 is a hexapeptide with the following structure:

D-Ala-D-2-Nal-Ala-Trp-D-Phe-Lys-NH₂

• Molecular formula: C₄₅H₅₅N₉O₆
• Molecular weight: 817.97 g/mol
• CAS Number: 158861-67-7

Structural features:

• D-Ala at position 1 — D-amino acid enhances protease resistance and oral stability
• D-2-Nal (D-2-naphthylalanine) at position 2 — critical for high-affinity GHS-R1a binding; also present in Ipamorelin
• D-Phe at position 5 — further protease resistance
• C-terminal amidation — standard modification for receptor binding and stability
• Compared to GHRP-6, GHRP-2 substitutes D-Ala for His at position 1 and D-2-Nal for D-Trp at position 2, which accounts for its different selectivity profile

Mechanism of Action

GHS-R1a Receptor Agonism

GHRP-2 is a high-affinity agonist of the growth hormone secretagogue receptor (GHS-R1a). Its binding affinity exceeds that of GHRP-6, contributing to its greater potency. Receptor activation triggers the same intracellular signaling cascade:

• Phospholipase C activation
• IP3-mediated calcium release
• PKC activation
• GH vesicle exocytosis from somatotrophs

GH Release Potency

GHRP-2 produces the highest peak GH levels among commonly studied GHRPs at equivalent doses. Comparative studies have ranked GH release potency as:

1. GHRP-2 (highest per-dose GH output)
2. Hexarelin (comparable peak but more rapid desensitization)
3. GHRP-6 (moderate)
4. Ipamorelin (moderate, but most selective)

Cortisol and Prolactin Effects

GHRP-2 stimulates cortisol and prolactin release to a greater degree than Ipamorelin but less than Hexarelin:

• Cortisol elevation: Mediated through stimulation of hypothalamic CRH neurons and possible direct adrenal effects. Typically returns to baseline within 1–2 hours
• Prolactin elevation: Modest and transient at standard doses; mechanism may involve hypothalamic dopamine pathway modulation

These effects are dose-dependent and considered clinically insignificant at standard research doses in most studies, but they are a common point of discussion when comparing GHRPs.

Appetite Effects

GHRP-2 produces mild to moderate appetite stimulation — significantly less than GHRP-6 but more than Ipamorelin. The reduced orexigenic effect is attributed to structural differences that alter the balance between pituitary GHS-R1a activation (GH release) and hypothalamic GHS-R1a activation (appetite).

Synergy with GHRH Analogs

Like all GHRPs, GHRP-2 demonstrates synergistic GH release when combined with GHRH analogs such as CJC-1295 no DAC or Sermorelin. The complementary mechanisms — GHRH priming GH synthesis while GHRP triggers release and suppresses somatostatin — produce a supraadditive response.

Research Summary

Pharmacokinetics

• Half-life: Approximately 30–60 minutes
• Onset of action: GH elevation within 10–15 minutes of subcutaneous injection
• Peak GH levels: 15–30 minutes post-injection
• Duration of GH elevation: 2–3 hours
• Peak cortisol elevation: 30–60 minutes, returning to baseline within 1–2 hours
• Route: Subcutaneous injection (primary); intravenous (diagnostic/research); intranasal (studied)
• Metabolism: Hepatic and renal clearance; D-amino acid substitutions provide protease resistance
• Food interaction: GH response blunted by food intake; fasting administration recommended

Dosing Protocols

The following dosing information is compiled from published research and community discussion for educational purposes only. No FDA-approved human dosing guidelines exist for most research peptides. Always consult a qualified healthcare professional.

Reconstitution

Dosing Schedule

Syringe Measurements (U-100 insulin syringe)

Cycle Guidelines

• Cycle length: 8-16 weeks
• Route: Subcutaneous injection
• Timing: Evening administration may align with natural nocturnal GH rhythms; administer fasted
• Injection sites: Rotate between abdomen, thighs, and upper arms

Common Discussion Topics

1. GHRP-2 vs. Ipamorelin — The most frequent comparison. GHRP-2 produces greater peak GH but with cortisol and prolactin trade-offs that Ipamorelin avoids. The choice often depends on whether maximal GH output or cleaner selectivity is prioritized.

2. Cortisol concerns — The cortisol elevation from GHRP-2, while transient, generates discussion particularly for those considering chronic use. The concern is whether repeated acute cortisol spikes could have cumulative effects, though most studies suggest the elevations are clinically insignificant at standard doses.

3. Prolactin monitoring — Some community protocols suggest periodic prolactin monitoring with chronic GHRP-2 use, though published data shows only modest, transient elevations.

4. Combination protocols — GHRP-2 + CJC-1295 no DAC is a common pairing for those who prefer maximal GH output over Ipamorelin's cleaner but potentially lower-amplitude profile.

5. Diagnostic approval in Japan — The Pralmorelin approval provides a degree of clinical validation that other GHRPs lack, though it is important to note this is for single-dose diagnostic use.

6. Desensitization — Like other GHRPs, discussion exists around whether chronic use leads to GHS-R1a downregulation and reduced responsiveness over time.

Related Compounds

• GHRP-6 — the foundational GHRP; comparable GH release with more appetite stimulation and less cortisol elevation
• Ipamorelin — the most selective GHRP; less peak GH but minimal cortisol, prolactin, and appetite effects
• CJC-1295 — a GHRH analog commonly combined with GHRPs for synergistic GH release
• Sermorelin — an alternative GHRH analog with FDA history
• Hexarelin — the most potent GHRP by peak amplitude but with rapid desensitization and the greatest cortisol/prolactin elevation
• MK-677 (Ibutamoren) — an oral non-peptide GHS-R1a agonist; long-acting alternative to injectable GHRPs