Peptide Monograph
GHRP-2
Growth Hormone Releasing Peptide-2 / Pralmorelin
At a Glance
Mechanism of Action
GHRP-2 (also known as pralmorelin or KP-102) is a synthetic hexapeptide that functions as a potent growth hormone secretagogue by binding to the growth hormone secretagogue receptor type 1a (GHS-R1a), the same receptor targeted by the endogenous ligand ghrelin. GHRP-2 represents a structural refinement of the first-generation GHRP-6, with modifications that confer greater GH-releasing potency and improved selectivity.[1]
Like GHRP-6, GHRP-2 activates the phospholipase C/inositol trisphosphate (PLC/IP3) signaling cascade in pituitary somatotrophs, increasing intracellular calcium and triggering GH exocytosis. This mechanism is complementary to GHRH signaling (which operates via cAMP), and co-administration of GHRP-2 with a GHRH analog produces synergistic GH release that significantly exceeds either compound alone.[2]
GHRP-2 retains some ghrelin-mimetic properties, including moderate appetite stimulation, but this effect is less pronounced than with GHRP-6. GHRP-2 also stimulates cortisol and prolactin release, though to a lesser degree than GHRP-6. This positions GHRP-2 as a second-generation GH secretagogue with an improved selectivity profile compared to GHRP-6 but less selective than the third-generation compound ipamorelin (which produces virtually no cortisol, prolactin, or appetite effects).[3]
GHRP-2 is notable for its approval in Japan under the trade name GHRP Kaken (pralmorelin) as a diagnostic agent for growth hormone deficiency. The reliability and reproducibility of the GH response to GHRP-2 make it well-suited for GH stimulation testing, and Japanese clinical practice guidelines include pralmorelin as a standard GH provocation test.[4]
Evidence Summary
GHRP-2 has been studied in clinical settings primarily as a diagnostic agent and pharmacological research tool. It is approved in Japan for GH deficiency diagnosis. No large-scale therapeutic efficacy trials have been completed outside Japan. All therapeutic applications beyond diagnosis are investigational.
GH Release Potency
Comparative studies have demonstrated that GHRP-2 produces a more robust GH release than GHRP-6 on a per-microgram basis. Bowers et al. showed that GHRP-2 is among the most potent of the synthetic hexapeptide GH secretagogues, with a GH response that exceeds GHRP-6 by approximately 30–50% at equivalent doses. Peak GH levels occur 15–30 minutes after subcutaneous or intravenous administration.[1][2]
Diagnostic Validation (Japan)
Pihoker et al. and subsequent Japanese clinical studies validated the reliability of GHRP-2 (pralmorelin) as a GH provocation agent. In the standardized test, 100 mcg of pralmorelin is administered intravenously, and serum GH is measured at 15, 30, 45, and 60 minutes. A peak GH response below defined cut-offs (typically 9–15 ng/mL depending on the assay) is considered indicative of GH deficiency. The test demonstrates excellent reproducibility and correlates well with insulin tolerance test results.[3][4]
Selectivity Profile
Howard et al. characterized the molecular pharmacology of GHS-R1a and demonstrated that different GH secretagogues activate the receptor with varying degrees of selectivity for downstream signaling pathways. GHRP-2 activates GH release more selectively than GHRP-6, with reduced cortisol and prolactin co-stimulation, but less selectively than ipamorelin. This intermediate selectivity profile has limited its therapeutic development in favor of more selective agents.[5]
Primary Uses (in Research)
Based on the available literature, GHRP-2 has been investigated for the following applications:
- GH deficiency diagnosis (approved in Japan) — Standardized IV provocation test using 100 mcg pralmorelin to assess pituitary GH reserve. Approved and routinely used in Japanese clinical practice.[4]
- GH axis stimulation — Research tool for studying GHS-R1a pharmacology, somatotroph function, and interactions between GHRP and GHRH signaling pathways.[1]
- Body composition research — Investigation of chronic GH secretagogue administration on lean body mass, fat mass, and metabolic parameters. Studies suggest favorable effects on body composition with sustained GH elevation, though data is limited.[2]
- Anti-aging research — Studied in the context of age-related GH decline (somatopause) to determine whether restoring pulsatile GH secretion improves age-related metabolic and body composition changes.
Contraindications
No established therapeutic contraindications exist outside Japan's diagnostic labeling. The following precautions are based on the peptide's known pharmacological mechanisms:
- Active malignancy — GH promotes cell proliferation and IGF-1 elevation. GH secretagogues should be avoided in individuals with active cancer or a history of GH-responsive tumors.
- Pregnancy and lactation — No reproductive toxicology data is available. Use is strongly discouraged.
- Diabetes mellitus — GHRP-2 can elevate blood glucose through GH-mediated insulin resistance. Diabetic patients may experience worsened glycemic control.
- Pituitary tumors — GH secretagogues may stimulate growth of pituitary adenomas. Avoid in patients with known or suspected pituitary tumors.
- Cushing's syndrome / hypercortisolism — GHRP-2 stimulates cortisol release, though less than GHRP-6. Use in patients with existing hypercortisolism may exacerbate the condition.[3]
- Known hypersensitivity — Discontinue use if signs of allergic reaction develop.
Standard Protocols
The following protocols are derived from clinical research studies and community-reported protocols. Outside of the Japanese diagnostic indication, no dosing regimen has been validated in pivotal human clinical trials. These should not be interpreted as medical prescriptions.
| Protocol | Route | Dose | Frequency | Duration |
|---|---|---|---|---|
| GH release (standard) | SubQ | 100 – 200 mcg | 2–3x daily | 8–12 weeks |
| GH release (higher dose) | SubQ | 200 – 300 mcg | 2–3x daily | 8–12 weeks |
| Combined with GHRH analog | SubQ | 100 mcg GHRP-2 + 100 mcg GHRH analog | 2–3x daily | 8–12 weeks |
| Diagnostic (Japan — pralmorelin) | IV bolus | 100 mcg | Single dose | N/A — GH measured at 15, 30, 45, 60 min |
As with other GH secretagogues, GHRP-2 is typically administered on an empty stomach (fasting for at least 30 minutes before and after) to maximize GH pulse amplitude. Common administration times are upon waking, pre-workout, and before bed. Saturation dose appears to be around 100–200 mcg, beyond which additional GH release is minimal while side effects increase.[2]
Common Stacks & Synergies
In the peptide research community, GHRP-2 is frequently combined with other compounds. The following stacks are commonly discussed but have limited or no published human clinical evidence supporting their combined therapeutic use:
- GHRP-2 + GHRH analog (CJC-1295 or Mod GRF 1-29) — The most widely used combination. Synergistic GH release via complementary PLC/IP3 (GHRP-2) and cAMP (GHRH) pathways. Well-supported by published pharmacology research demonstrating that combined administration produces GH release several-fold greater than either agent alone.[2]
- GHRP-2 + Ipamorelin — Some protocols combine second-generation (GHRP-2) and third-generation (ipamorelin) secretagogues. The rationale is unclear given overlapping receptor targets; ipamorelin is generally preferred as a standalone due to superior selectivity.
- GHRP-2 + BPC-157 or TB-500 — Anecdotally combined in tissue repair protocols. GH elevation from GHRP-2 is theorized to complement the healing properties of BPC-157 or TB-500. No controlled evidence supports this combination.
Preparation & Administration
GHRP-2 is supplied as a lyophilized (freeze-dried) powder in vials, typically containing 5 mg or 10 mg of peptide. It must be reconstituted with bacteriostatic water (BAC water) before injection.
Reconstitution
For a standard 5 mg vial reconstituted with 2.5 mL of bacteriostatic water, each 0.1 mL (10 units on a standard insulin syringe) delivers 200 mcg. For detailed step-by-step reconstitution instructions and a concentration calculator, see the Reconstitution Guide.
Injection
Subcutaneous injections should be administered using a 29–31 gauge insulin syringe. Common injection sites include the abdominal subcutaneous tissue (periumbilical area). Rotate injection sites to avoid lipodystrophy. For injection technique, site selection, and sterile procedure, see the Injection Safety Guide.
Intranasal
Intranasal GHRP-2 has been explored in research settings. Bioavailability via the intranasal route is lower than subcutaneous, and dosing adjustments are required. This route is not well-standardized and is not commonly used in research protocols.
Side Effects & Adverse Events
The adverse event profile described below is drawn from phase 1/2 clinical studies, the Japanese diagnostic approval data, and uncontrolled reports. Long-term safety data from large-scale therapeutic trials is not available.
Commonly reported side effects:
- Hunger increase (moderate): GHRP-2 stimulates appetite through ghrelin receptor agonism, but the effect is notably less intense than GHRP-6. Most users report a moderate increase in appetite within 20–30 minutes of administration.[3]
- Water retention: Mild fluid retention, potentially manifesting as puffy appearance or slight weight gain.
- Cortisol elevation: Measurable but less than GHRP-6. Chronic use may contribute to insulin resistance.
- Prolactin elevation: Less pronounced than GHRP-6 but still measurable, particularly at higher doses.[3]
- Numbness and tingling: Transient paresthesias in hands and feet related to acute GH release.
- Joint pain: Arthralgia associated with GH-mediated fluid retention.
- Injection site reactions: Redness, swelling, or mild pain at the injection site.
- Flushing and warmth: Reported occasionally after injection.
Drug Interactions
No formal drug interaction studies have been conducted with GHRP-2 for therapeutic use. The following theoretical interactions are based on the peptide's known pharmacological mechanisms:
- Insulin and oral hypoglycemics — GH elevates blood glucose via insulin resistance. Diabetic patients using insulin or sulfonylureas may require dose adjustments. Monitor blood glucose closely.
- Corticosteroids — GHRP-2 stimulates cortisol release. Concurrent exogenous corticosteroid use may amplify hypercortisolism-related adverse effects.
- Somatostatin analogs (octreotide, lanreotide) — Somatostatin suppresses GH release and will antagonize the effects of GHRP-2. Concurrent use is counterproductive.
- Other GH secretagogues — Combining multiple GHS-R1a agonists (GHRP-2, GHRP-6, ipamorelin, MK-677) may produce additive side effects without proportional GH benefit due to receptor saturation.
Storage & Handling
| Form | Condition | Stability |
|---|---|---|
| Lyophilized powder (sealed) | Room temperature (below 25°C / 77°F), away from direct light | Stable for extended periods (months to years if sealed) |
| Lyophilized powder (sealed) | Refrigerated (2–8°C / 36–46°F) | Optimal for long-term storage |
| Reconstituted solution | Refrigerated (2–8°C / 36–46°F) | Use within 28 days |
| Reconstituted solution | Room temperature | Not recommended; use within 24–48 hours if unavoidable |
Do not freeze reconstituted solution. Protect from prolonged light exposure. If the solution appears cloudy, discolored, or contains particulate matter, discard the vial. Always use bacteriostatic water (not sterile water) for reconstitution to provide antimicrobial preservation for multi-dose use.
Legal & Regulatory Status
- Japan (PMDA) — Approved as a diagnostic agent for GH deficiency under the trade name GHRP Kaken (pralmorelin). Available by prescription for GH stimulation testing in clinical settings.[4]
- FDA (United States) — Not approved for any indication. Not scheduled as a controlled substance. Sold under the research chemical designation "not for human consumption."
- European Union (EMA) — Not approved as a medicinal product. Available as a research chemical.
- WADA (World Anti-Doping Agency) — Prohibited at all times under class S2 (Peptide Hormones, Growth Factors, Related Substances, and Mimetics). Athletes subject to anti-doping testing should not use GHRP-2.
- Australia (TGA) — Not approved. Classified as a Schedule 4 prescription-only substance.
Open Questions
Key unresolved questions regarding GHRP-2 include:
- Therapeutic potential beyond diagnosis — Whether GHRP-2 has genuine therapeutic utility for GH deficiency treatment, age-related sarcopenia, or body composition improvement, beyond its established diagnostic role, remains untested in large-scale trials.
- Comparison with newer agents — How GHRP-2 compares clinically with ipamorelin (more selective) or tesamorelin (FDA-approved GHRH analog) for sustained GH elevation and clinical outcomes has not been formally assessed.
- Long-term safety of chronic GHS-R1a agonism — The consequences of prolonged ghrelin receptor activation on metabolic health, appetite regulation, and cancer risk are not established.
- Intranasal bioavailability — Whether intranasal administration can achieve clinically meaningful GH release with acceptable reproducibility remains an open question.
- Optimal diagnostic cut-offs — GH assay variability across laboratories means that universal diagnostic thresholds for the pralmorelin stimulation test are not firmly established outside Japan.
Bibliography
- Bowers CY. "Growth hormone-releasing peptide (GHRP)." Cell Mol Life Sci. 1998;54(12):1316-1329. doi:10.1007/s000180050257. PMID:9893709.
- Bowers CY, Reynolds GA, Durham D, Barrera CM, Pezzoli SS, Thorner MO. "Growth hormone (GH)-releasing peptide stimulates GH release in normal men and acts synergistically with GH-releasing hormone." J Clin Endocrinol Metab. 1990;70(4):975-982. doi:10.1210/jcem-70-4-975. PMID:2108187.
- Pihoker C, Badger TM, Reynolds GA, Bowers CY. "Treatment effects of intranasal growth hormone releasing peptide-2 (GHRP-2) in children with short stature." J Endocrinol. 1997;155(1):79-86. doi:10.1677/joe.0.1550079. PMID:9390007.
- Muccioli G, Tschop M, Papotti M, Deghenghi R, Heiman M, Ghigo E. "Neuroendocrine and peripheral activities of ghrelin: implications in metabolism and obesity." Eur J Pharmacol. 2002;440(2-3):235-254. doi:10.1016/S0014-2999(02)01432-2. PMID:12007539.
- Howard AD, Feighner SD, Cully DF, Arena JP, Liberator PA, Rosenblum CI, Hamelin M, Hreniuk DL, Palyha OC, Anderson J, Paress PS, Diaz C, Chou M, Liu KK, McKee KK, Pong SS, Chaung LY, Elbrecht A, Dashkevicz M, Heavens R, Rigby M, Sirinathsinghji DJ, Dean DC, Melillo DG, Van der Ploeg LH. "A receptor in pituitary and hypothalamus that functions in growth hormone release." Science. 1996;273(5277):974-977. doi:10.1126/science.273.5277.974. PMID:8688086.