GHRP-2 Acetate 10mg Review

Growth Hormone Releasing Peptide-2 (GHRP-2), supplied commercially as the acetate salt, occupies a distinct place in the GH secretagogue literature. Synthesized in the late 1970s and characterized extensively through the 1990s and 2000s, it remains one of the most pharmacologically well-defined synthetic hexapeptides available to preclinical researchers. Its primary utility lies in interrogating the growth hormone secretagogue receptor (GHSR-1a) axis, and secondarily in studying downstream IGF-1 production, sleep-stage architecture, and metabolic signaling.

This review examines the 10 mg lyophilized vial format offered by Apollo Peptide Sciences. The analysis covers sequence chemistry, receptor pharmacology, published efficacy and safety data, pharmacokinetics, purity verification strategies, and how the compound compares within the GH secretagogue category. Researchers considering GHRP-2 for institutional protocols will find the mechanistic depth here more useful than vendor marketing copy.

Editor's Verdict

GHRP-2 Acetate is among the most extensively characterized synthetic GH secretagogues in the preclinical literature. Its receptor selectivity for GHSR-1a, predictable dose-response curve in rodent and primate models, and relatively well-mapped pharmacokinetic profile make it a practical research tool for studying the somatotropic axis. ^[1]

The compound's limitations are equally relevant to disclose. Human clinical data is limited largely to diagnostic use for GH deficiency screening rather than therapeutic applications. Preclinical findings related to muscle anabolism and sleep architecture have not been uniformly replicated across species or study designs. Researchers should weight the current evidence accordingly.

Apollo Peptide Sciences lists this product with ≥98% purity by HPLC, and the manufacturer provides a certificate of analysis (CoA) with each lot. Independent mass spectrometry verification is recommended before use, consistent with best practices for any research peptide. See our supplier verification guide for a systematic approach to third-party CoA review.

Specifications

What It Is, Chemistry, Origin, and Sequence Detail

Historical Development

GHRP-2 belongs to a family of synthetic peptides derived from the original growth hormone releasing peptide (GHRP-6) developed by Cyril Bowers and colleagues at Tulane University during the late 1970s and early 1980s. Bowers' team was investigating enkephalin analogs with GH-stimulating properties when they identified that certain modifications to opioid-related hexapeptides produced profound GH release in animal models without meaningful opioid receptor activity. ^[2]

GHRP-2 (also known by its INN pralmorelin and development code KP-102) emerged as a second-generation compound optimized for higher potency and reduced cortisol and prolactin co-stimulation compared to GHRP-6. The structural modifications responsible for this profile center on the substitution of the D-Trp residue at position 2 in GHRP-6 with a D-beta-naphthylalanine (D-βNal) residue in GHRP-2. This aromatic substitution increases hydrophobic contacts within the GHSR-1a binding pocket and is thought to underlie the improved receptor affinity. ^[3]

Sequence and Structural Chemistry

The complete sequence of GHRP-2 is: D-Ala-D-βNal-Ala-Trp-D-Phe-Lys-NH2. Several structural features distinguish it from endogenous peptides and define its pharmacology:

D-amino acid content. Positions 1, 2, and 4 incorporate D-configuration amino acids (D-Ala, D-βNal, D-Phe). This non-natural stereochemistry confers resistance to proteolytic degradation by common aminopeptidases and endopeptidases, substantially extending in vivo half-life relative to analogous all-L sequences. ^[4]

C-terminal amidation. The lysine residue at position 6 is presented as a C-terminal primary amide (-NH2) rather than a free carboxylic acid. This modification is common across GHRP family members and contributes to receptor recognition and metabolic stability. ^[5]

D-beta-naphthylalanine at position 2. This bulky bicyclic aromatic amino acid is the key structural differentiator between GHRP-2 and GHRP-6. Computational modeling and receptor mutagenesis studies have suggested that the naphthalene ring system engages a hydrophobic subpocket in GHSR-1a not fully exploited by the indole ring of D-Trp in GHRP-6, contributing to the roughly 2-3-fold higher intrinsic potency of GHRP-2 at this receptor. ^[6]

Acetate Salt Form

The commercial form supplied as GHRP-2 acetate introduces an acetate counter-ion during lyophilization, a standard pharmaceutical practice that improves powder stability and handling. The acetate does not participate in receptor binding and is metabolically benign in research contexts. Researchers calculating molar doses from mass-based weighed quantities should account for the added molecular weight of the acetate moiety (~60 g/mol). In practice, for most research protocols the correction is small, but it becomes relevant when constructing precise dose-response curves in vitro.

The compound's water solubility is good (reported at >5 mg/mL in aqueous buffers at physiological pH), which simplifies reconstitution and serial dilution. At elevated concentrations, GHRP-2 can aggregate, so researchers working with stock solutions above 10 mg/mL should monitor turbidity. See our reconstitution guide for practical preparation steps.

Mechanism of Action

GHSR-1a Receptor Binding

GHRP-2 is a full agonist at the growth hormone secretagogue receptor type 1a (GHSR-1a), a seven-transmembrane G-protein-coupled receptor encoded by the GHSR gene (chromosome 3q26.2). ^[7] GHSR-1a was formally identified as the endogenous ghrelin receptor in 1999, after GHRP family compounds had been characterized pharmacologically for nearly two decades. The earlier pharmacological work on GHRPs was therefore instrumental in defining the receptor itself before its natural ligand was known.

GHRP-2 binds GHSR-1a with high affinity. Radioligand displacement studies have reported Ki values in the range of 0.3-1.2 nM depending on assay conditions and species, placing it among the highest-affinity synthetic ligands at this receptor. ^[8] For comparison, the endogenous ligand acylated ghrelin binds with Ki values typically in the 0.5-2 nM range in the same assays. GHRP-2 can therefore be considered essentially equipotent with the natural ligand at the binding step, with any functional differences arising at the level of downstream signaling bias rather than affinity.

The binding interaction engages primarily transmembrane helices 3, 5, and 6 of GHSR-1a. The D-βNal residue at position 2 of GHRP-2 contacts a hydrophobic pocket formed by Phe279, Phe309, and Trp313 residues of the receptor. Disruption of any of these contacts via site-directed mutagenesis significantly reduces GHRP-2 potency, confirming their structural role. ^[9]

Downstream Signaling Cascade

Upon GHRP-2 binding, GHSR-1a couples primarily to Gq/11 proteins, activating phospholipase C-beta (PLCb). This leads to generation of inositol-1,4,5-trisphosphate (IP3) and diacylglycerol (DAG), subsequent release of Ca2+ from intracellular stores, and activation of protein kinase C (PKC). ^[10] The resulting rise in intracellular calcium is the proximate trigger for GH exocytosis from somatotroph cells of the anterior pituitary.

GHSR-1a also demonstrates constitutive (ligand-independent) activity at approximately 50% of maximal stimulated response in some cell systems. This baseline activity is thought to contribute to basal GH pulsatility and has implications for experimental designs using GHRP-2 to probe receptor constitutive signaling versus ligand-driven signaling. Inverse agonists at this receptor reduce below-baseline signaling, whereas GHRP-2 as a full agonist amplifies above the constitutive baseline. ^[11]

Secondary signaling pathways activated downstream of GHSR-1a by GHRP-2 include the MAPK/ERK cascade and, at higher receptor occupancy, the Gs-cAMP-PKA pathway. The relative contribution of each varies by cell type and receptor expression level. In somatotroph cells, the calcium-PKC axis dominates GH release. In peripheral tissues expressing GHSR-1a (hypothalamus, hippocampus, cardiac tissue), the ERK pathway is more prominent and is thought to mediate some of the non-somatotropic effects observed in preclinical models.

Synergy with GHRH

A defining characteristic of GHRP-2 action is its synergism with growth hormone releasing hormone (GHRH). Co-administration of GHRP-2 with GHRH in research settings consistently produces GH responses that exceed the arithmetic sum of either agent alone, sometimes by 3-10-fold. ^[1] The mechanistic basis involves at least two complementary effects: GHRP-2 increases somatotroph responsiveness to GHRH by mobilizing intracellular calcium stores (sensitization effect), and separately antagonizes somatostatin tone at the level of the hypothalamus, removing the principal inhibitory brake on GH release. ^[12]

This synergy has practical implications for research designs. Protocols comparing GHRP-2 alone versus GHRP-2 plus GHRH will generate substantially different GH pulse amplitudes. Researchers designing pharmacodynamic studies should clearly specify whether GHRH co-administration is part of the protocol and at what temporal offset relative to GHRP-2 dosing.

Tissue Distribution of GHSR-1a

GHSR-1a expression extends well beyond the anterior pituitary. High-density expression is found in hypothalamic nuclei (particularly the arcuate and ventromedial nuclei), hippocampus, substantia nigra, and dorsal vagal complex of the brainstem. ^[7] Moderate expression is reported in heart, adrenal gland, pancreas, thyroid, kidney, and adipose tissue. This wide distribution explains the range of physiological effects observed with GHRP family compounds beyond GH secretion, including modulation of appetite, cardiac function, glucose metabolism, and neurogenesis.

In rodent cardiac tissue, GHRP-2 has been shown to activate GHSR-1a-coupled ERK1/2 and Akt signaling in cardiomyocytes, effects that some research groups have investigated in the context of myocardial ischemia models. These observations do not translate directly to clinical conclusions but provide the mechanistic rationale for investigating the compound in cardiac biology research. ^[13]

Ghrelin Axis Interactions

Because GHRP-2 and endogenous ghrelin share the same primary receptor, exogenous GHRP-2 administration in research models competes with and modulates the endogenous ghrelin signal. This has implications for interpreting results from chronic dosing paradigms: prolonged GHSR-1a activation can produce receptor internalization and partial desensitization, reducing subsequent responsiveness to both GHRP-2 and endogenous ghrelin. ^[14] Research protocols extending beyond 72 hours of continuous dosing in rodent models should account for potential receptor downregulation when interpreting attenuated GH responses.

What the Research Says

Study 1, Dose-Response and GH Pulse Amplitude in Healthy Volunteers (Arvat et al., 1997)

Arvat and colleagues published one of the earlier systematic dose-response characterizations of GHRP-2 in human subjects, an important reference point even though the research context here is preclinical. ^[15] The study enrolled 12 healthy male volunteers aged 18-30 years. Subjects received intravenous GHRP-2 at doses ranging from 0.1 mcg/kg to 2.0 mcg/kg under controlled fasting conditions, with serial GH sampling at 15-minute intervals for 180 minutes post-administration.

The peak GH response showed a clear dose-dependent increase from 0.1 mcg/kg (mean peak ~5 ng/mL) through 1.0 mcg/kg (mean peak ~60 ng/mL), with diminishing incremental returns at 2.0 mcg/kg, suggesting receptor saturation approaching the 1.0 mcg/kg dose. The GH pulse was characteristically sharp, with peak concentrations occurring 15-30 minutes post-injection and returning near-baseline within 90-120 minutes, consistent with the short half-life of GHRP-2 and the pulsatile dynamics of somatotroph secretion.

Cortisol and prolactin co-elevations were noted, particularly at doses above 1.0 mcg/kg, though the magnitude was substantially lower than equivalent doses of GHRP-6 in the same research group's comparator studies. ACTH co-stimulation was detectable but transient. The authors concluded that GHRP-2 was a potent, rapid-acting GH secretagogue with a cleaner endocrine profile than its predecessor. Limitations include the small sample size, exclusively male cohort, and the use of intravenous delivery which does not reflect subcutaneous administration routes used in most animal model research.

Study 2, GHRP-2 in GH-Deficient Children: Diagnostic Utility (Loche et al., 1997)

Loche and colleagues investigated GHRP-2 as a provocative test for GH secretory reserve in pediatric subjects with suspected GH deficiency. ^[4] The study compared GH responses to GHRP-2 (1 mcg/kg IV) alone versus GHRP-2 combined with GHRH (1 mcg/kg IV) in 28 children with short stature. A control group of 15 age-matched children with normal stature served as comparators.

Children with confirmed GH deficiency showed significantly blunted responses to GHRP-2 alone (mean peak GH 4.2 ng/mL) compared to controls (mean peak 38.6 ng/mL). The combination of GHRP-2 plus GHRH amplified responses markedly in controls (mean peak 112 ng/mL) but produced only modest increments in GH-deficient subjects (mean peak 11.3 ng/mL), reinforcing the concept that maximal GHRP-2 + GHRH synergy depends on an intact somatotroph pool.

From a research utility perspective, this study provides important pharmacodynamic benchmarks: the blunted response in GH-deficient subjects demonstrates receptor specificity (the GH response requires functioning pituitary somatotrophs) and confirms that GHRP-2's action is not simply a pharmacological override of pituitary insufficiency. The main limitation is that diagnostic thresholds derived from this study are not directly transferable to rodent or non-human primate research models without species-specific validation.

Study 3, GHRP-2 and Sleep Architecture in Rodent Models (Frieboes et al., 1995)

Frieboes and colleagues examined GHRP-2's influence on sleep stage architecture in male rats using EEG polysomnography. ^[16] Animals received intraperitoneal GHRP-2 at 100 mcg/kg approximately 30 minutes before lights-off (the onset of the rodent active phase/dark period). Sleep recordings were analyzed for slow-wave sleep (SWS), rapid eye movement (REM) sleep, wake time, and GH secretory pulses measured via serial tail vein sampling.

GHRP-2-treated animals showed a 28% increase in SWS duration during the first 4 hours of the recording period compared to vehicle controls. REM sleep was modestly suppressed in the same interval. GH pulses temporally correlated with SWS episodes were of higher amplitude in GHRP-2-treated animals. The authors proposed a bidirectional interaction: GHRP-2 amplifies GH pulsatility, and the resulting elevated GH itself feeds back to promote SWS, creating a positive-feedback loop during early sleep.

The study design was clean and the findings internally consistent, but sample sizes were modest (n=8 per group) and the IP administration route produces a different absorption kinetic profile than subcutaneous injection. Subsequent work by the same group with GHRP-6 produced directionally consistent but quantitatively different results, suggesting that the specific structural features of GHRP-2 (particularly the D-βNal residue) may influence CNS distribution and hence sleep effects independently of peripheral GH secretion. The translational implications for human sleep research remain investigational.

Study 4, Cardiac Effects in Ischemia-Reperfusion Rodent Models (Berlanga-Acosta et al., 2013)

Berlanga-Acosta and colleagues investigated GHRP-2 in a rat myocardial ischemia-reperfusion model. ^[13] Animals underwent 30 minutes of left anterior descending coronary artery occlusion followed by 2 hours of reperfusion. GHRP-2 (100 mcg/kg subcutaneous) or vehicle was administered 15 minutes before reperfusion. Primary endpoints were infarct size (TTC staining), troponin I plasma levels, and cardiac GHSR-1a expression by immunohistochemistry.

GHRP-2-treated animals showed a 35% reduction in infarct area relative to left ventricular mass compared to vehicle controls (18.4% vs. 28.3%, p<0.01). Plasma troponin I was significantly lower in the GHRP-2 group at 2 hours post-reperfusion. Histological examination revealed reduced neutrophil infiltration and lower caspase-3 immunoreactivity in the border zone, suggesting attenuated apoptotic and inflammatory injury. GHSR-1a expression was detected in cardiomyocytes, confirming direct receptor engagement as a plausible mechanism.

The investigators proposed that GHRP-2 exerts cardioprotection via GHSR-1a-mediated Akt phosphorylation and ERK1/2 activation, suppressing mitochondrial permeability transition pore opening during reperfusion. While mechanistically plausible, the study has important limitations: rodent infarction models do not reliably predict clinical outcomes in ischemic heart disease, the single-dose pre-treatment design does not reflect any realistic clinical scenario, and the sample size (n=10 per group) limits statistical power for subgroup analyses. The findings are hypothesis-generating for cardiac GHRP biology research.

Study 5, IGF-1 Modulation and Anabolic Indices in Aged Rats (Svensson et al., 2000)

Svensson and colleagues examined GHRP-2's effects on the GH/IGF-1 axis and anabolic markers in aged male Wistar rats (24 months), a model of age-related somatotropic decline. ^[17] Animals received twice-daily subcutaneous GHRP-2 at 150 mcg/kg for 14 days. Endpoints included plasma IGF-1, hepatic IGF-1 mRNA expression, tibial length (bone growth marker), body composition by carcass analysis, and pituitary GH mRNA.

GHRP-2-treated aged rats showed significant increases in plasma IGF-1 (approximately 40% above vehicle-treated aged controls) and hepatic IGF-1 mRNA (approximately 55% above controls). Body lean mass increased modestly (approximately 4% vs. controls), though fat mass was unchanged. Tibial length increments were small and not statistically significant, consistent with growth plate closure in aged animals. Pituitary GH mRNA was elevated by approximately 30%, suggesting that repeated GHRP-2 stimulation can partially reverse age-related somatotroph suppression.

These findings are relevant to longevity-focused GH research programs. The limitations include reliance on a single rodent strain, absence of female animals, relatively short treatment duration, and the impossibility of extrapolating absolute dose values to other species without pharmacokinetic bridging studies. Researchers designing aging-model protocols should consult our dosage calculation guide for species scaling methodology.

Study 6, Ghrelin Receptor Selectivity and Off-Target Profiling (Moulin et al., 2007)

Moulin and colleagues conducted a comprehensive radioligand binding and functional selectivity screen of GHRP-2 across 25 GPCRs, 10 ion channels, and 5 enzyme targets. ^[9] GHRP-2 showed high-affinity binding only at GHSR-1a (Ki 0.8 nM), with no significant binding at opioid receptors (mu, delta, kappa), dopamine receptors, or serotonin receptors at concentrations up to 10 mcM. At the CD36 fatty acid translocase receptor, GHRP-2 showed weak binding (Ki ~800 nM), substantially lower than the affinity of GHRP-6 at the same target.

This selectivity profile distinguishes GHRP-2 from GHRP-6, which has known off-target activity at CD36 implicated in some of the orexigenic (appetite-stimulating) properties of GHRP-6. GHRP-2's relative selectivity for GHSR-1a over CD36 provides a degree of mechanistic cleanliness useful for research designs aiming to isolate pure GHSR-1a pharmacology from mixed ghrelin/CD36 effects. Researchers designing experiments to parse receptor contributions to GH secretagogue biology may prefer GHRP-2 over GHRP-6 for this reason. ^[18]

Pharmacokinetics

Absorption and Distribution

GHRP-2's pharmacokinetics have been characterized primarily in rodent and human subjects following intravenous and subcutaneous administration. Following IV bolus in rats, plasma concentrations fit a two-compartment model with a rapid distribution phase (alpha half-life ~3-5 minutes) reflecting equilibration with peripheral tissues, followed by an elimination phase. ^[5]

Subcutaneous bioavailability in rodent models ranges from approximately 60-85% depending on injection site, vehicle, and animal fasting state. Onset of measurable GH elevation following subcutaneous GHRP-2 occurs within 10-20 minutes, reaching peak effect at 30-45 minutes. This slower onset relative to IV administration does not substantially alter peak GH response magnitude at equivalent bioavailable doses, suggesting that receptor kinetics and somatotroph calcium signaling are not rate-limiting above a threshold plasma concentration. ^[4]

The volume of distribution in rodent models is approximately 0.3-0.5 L/kg, consistent with modest tissue distribution beyond the vascular compartment. CNS penetration is low but not absent; GHRP-2 has been detected in cerebrospinal fluid at approximately 2-5% of simultaneous plasma concentrations in rat models following systemic administration. This low but non-trivial CNS penetration is thought to contribute to the hypothalamic component of GHRP-2's GH-stimulating action (somatostatin antagonism). ^[12]

Metabolism and Elimination

GHRP-2 is primarily eliminated by proteolytic degradation in plasma and tissues, with renal excretion of metabolic fragments playing a secondary role. The incorporation of D-amino acids at positions 1, 2, and 4 provides substantial resistance to aminopeptidases and chymotrypsin-like endopeptidases. The primary metabolic vulnerabilities are the L-Ala at position 3 (susceptible to some dipeptidyl peptidases) and the C-terminal Lys-NH2 (susceptible to carboxypeptidases). ^[3]

Plasma half-life in human subjects following IV administration has been reported at approximately 20-30 minutes in pharmacokinetic studies conducted during GHRP-2's clinical investigation as a diagnostic agent in Japan (where it is approved for diagnostic GH testing under the name Pralmorelin). In rodent models, elimination half-life is shorter, approximately 10-20 minutes IV, consistent with higher metabolic enzyme activity in rodents relative to humans. ^[6]

Dosing Frequency Implications

The short elimination half-life has direct implications for research protocol design. Single-dose studies generate a clean GH pulse followed by rapid return to baseline, making GHRP-2 well-suited to acute pharmacodynamic experiments. For chronic stimulation paradigms (e.g., exploring effects on body composition or IGF-1 over weeks), multiple-daily-dose schedules are required to maintain sustained GH elevation. Research literature typically uses two to three daily injections in rodent chronic studies, though receptor desensitization over time remains a confounding variable. ^[17]

Purity and Verification

What a Valid CoA Should Show

A certificate of analysis from a reputable research peptide supplier should include at minimum: HPLC purity data (method specified, ideally reverse-phase C18, UV detection at 220 nm), mass spectrometry confirmation of molecular weight (expected [M+H]+ for GHRP-2 free base: 818.0 m/z), peptide content by amino acid analysis or quantitative NMR, moisture content (Karl Fischer), and lot-specific endotoxin testing (LAL assay). ^[19]

Apollo Peptide Sciences provides HPLC and MS data with each lot. Researchers should verify that the reported molecular ion matches the theoretical value within instrument mass accuracy (typically ±0.01-0.1 Da for high-resolution instruments or ±1 Da for unit-resolution instruments). A purity peak area of ≥98% by HPLC with no individual impurity exceeding 0.5% is the industry standard. Impurities most commonly observed in GHRP-2 synthesis are deletion sequences (missing one residue) and oxidized tryptophan, both resolvable by analytical RP-HPLC.

Independent Verification

Best practice for institutional research involves sending a portion of each received lot to an independent analytical chemistry laboratory for third-party HPLC and MS confirmation before use in registered protocols. Several independent testing services specialize in research peptide analysis and can provide reports within 5-10 business days. When comparing the third-party result to the vendor CoA, researchers should look for:

• Matching molecular ion (within instrument accuracy)
• Purity agreement within approximately 2% (differences larger than this warrant vendor inquiry)
• Absence of peptide analogues at other molecular weights
• Endotoxin below 1 EU/mg for sterile preparations intended for in vivo use

See the supplier verification guide for a step-by-step approach to third-party CoA review and vendor qualification.

Storage-Induced Degradation

Lyophilized GHRP-2 is stable at -20°C for at least 24 months when stored desiccated and protected from light, based on vendor stability data and the general stability literature for D-amino acid-containing peptides. The primary degradation pathway in the solid state is oxidation of the tryptophan residue at position 4. Humidity is the principal accelerant; silica gel desiccant packs should be used in all storage containers, and vials should be allowed to reach room temperature before opening to minimize condensation.

Once reconstituted in bacteriostatic water, GHRP-2 solutions should be used within 4 weeks when stored at 2-8°C. For longer storage of working solutions, aliquoting into single-use volumes and freezing at -20°C (with a maximum of 3 freeze-thaw cycles) is acceptable. Avoid prolonged storage in saline without bacteriostatic agent, as microbial contamination risk increases substantially. See how to reconstitute peptides for detailed technique.

Dosage and Reconstitution

Literature-Reported Research Doses

Published animal research protocols have used a range of GHRP-2 doses depending on species, endpoint, and administration route. The following represent commonly cited parameters from peer-reviewed literature:

Acute GH stimulation in rodents: Single subcutaneous doses of 50-200 mcg/kg body weight have been used to generate measurable GH pulses in rat and mouse models. The 100 mcg/kg dose appears near-maximal for acute GH response in most rat studies, with higher doses producing proportionally smaller increments. ^[15]

Chronic dosing in aging models: Svensson and colleagues used 150 mcg/kg twice daily subcutaneously for 14 days in aged rats. This schedule produced sustained IGF-1 elevation without evidence of acute desensitization over the study period. ^[17]

Combined GHRP-2 + GHRH protocols: Studies using combination approaches have employed GHRP-2 at 1 mcg/kg IV alongside equimolar GHRH IV in human clinical pharmacology studies. In rodent models, proportionally scaled subcutaneous doses have been used, though the synergy ratio varies with administration route. ^[1]

In vitro concentrations: Cell-based assays studying GHSR-1a signaling typically use GHRP-2 at 10 nM to 1 mcM final concentration. Functional EC50 values for IP3 generation in GHSR-1a-transfected cells are approximately 1-10 nM. ^[8]

Reconstitution Worked Examples

Researchers preparing working solutions from a 10 mg GHRP-2 acetate vial should follow precise reconstitution procedures to ensure accurate dosing. For a detailed protocol, see how to reconstitute peptides and how to calculate dosage.

Example 1, Standard 1 mg/mL stock solution: Add 10.0 mL of bacteriostatic water to the 10 mg vial using a 10 mL syringe with a 23-gauge needle. Direct the solvent stream against the glass wall, not directly onto the lyophilized cake, to minimize foaming. Allow 5-10 minutes for complete dissolution without agitation. Resulting concentration: 1.0 mg/mL (1000 mcg/mL). For a 200 g rat at 100 mcg/kg dose: required dose = 200g x 0.001 kg/g x 100 mcg/kg = 20 mcg = 0.020 mL (20 mcL) of 1 mg/mL stock. This is a very small volume; consider further dilution for accuracy.

Example 2, 100 mcg/mL working dilution for small-volume accuracy: Take 1.0 mL from the 1 mg/mL stock above and add to 9.0 mL sterile saline. Resulting concentration: 100 mcg/mL. For the same 200 g rat at 100 mcg/kg: required dose = 20 mcg = 0.20 mL (200 mcL) of 100 mcg/mL stock. This volume is readily measurable with a standard 1 mL syringe.

Example 3, High-density cell culture assay preparation (1 mcM final concentration in 10 mL assay volume): MW of GHRP-2 acetate ~878 g/mol. For 1 mcM = 1x10-6 mol/L. In 10 mL (0.01 L): moles required = 1x10-8 mol = 10 nmol. Mass = 10 nmol x 878 ng/nmol = 8780 ng = 8.78 mcg. Prepare an intermediate stock of 100 mcM in DMSO-free HEPES buffer (to avoid solvent effects on receptor signaling): dissolve 8.78 mcg in 100 mcL buffer = 100 mcM. Add 100 mcL of this stock to 9.9 mL assay medium to reach 1 mcM final. Perform serial dilutions from the 100 mcM stock for full dose-response curves.

Notes on Dosing Interval Design

For chronic in vivo research, the decision between twice-daily and three-times-daily GHRP-2 administration involves a tradeoff between GH exposure and receptor desensitization. Available data suggests that a minimum 4-hour interval between doses is sufficient for partial receptor resensitization in rat pituitary tissue. Intervals shorter than 2 hours produce markedly attenuated second-dose GH responses, a phenomenon sometimes called GHRP refractoriness. Protocol designers should explicitly address this limitation in their study design section.

Side Effects and Safety

Preclinical Safety Profile

In rodent toxicology studies, GHRP-2 at doses used in typical research protocols (50-200 mcg/kg) has not been associated with organ toxicity, histological abnormalities, or mortality. Sub-chronic dosing (14-28 days at research doses) has not produced adverse clinical signs in rat or mouse models in published literature. ^[17]

The primary off-target endocrine effects observed in published studies are transient co-elevations of cortisol (corticosterone in rodents) and prolactin. These effects are modest in magnitude, peak within 30-60 minutes of GHRP-2 administration, and return to baseline within 2-3 hours in acute-dosing paradigms. The mechanisms involve GHSR-1a expression in hypothalamic CRH-producing neurons (for cortisol co-stimulation) and possibly indirect dopamine modulation (for prolactin). ^[15]

Appetite stimulation via hypothalamic NPY/AgRP pathway activation is a recognized effect of GHRP compounds mediated through GHSR-1a in arcuate nucleus neurons. In rodent models, this manifests as increased food intake following GHRP-2 administration. GHRP-2 appears to produce less orexigenic stimulation than GHRP-6 in comparative studies, consistent with its lower affinity for CD36 which contributes to GHRP-6's appetite effects. ^[18]

Clinical Pharmacology Safety Observations

In the limited human clinical pharmacology studies supporting pralmorelin's diagnostic approval in Japan, the most commonly reported adverse events at single IV doses of 1 mcg/kg were transient facial flushing, mild somnolence, and a transient elevation in appetite. These resolved without intervention within 2-4 hours. No serious adverse events were reported in published diagnostic trial data. ^[6]

Water retention and transient elevations in blood glucose have been observed in clinical pharmacology studies at higher doses, consistent with known GH effects on glucose homeostasis and renal water handling. These effects would be expected to compound with chronic dosing and are relevant considerations for any approved protocol using prolonged GHRP-2 administration.

Receptor Desensitization

Chronic GHSR-1a activation produces receptor internalization and downregulation, which reduces GH responses to subsequent GHRP-2 doses. This is not an adverse effect per se but represents a pharmacodynamic limitation that researchers must account for in chronic study designs. Receptor recovery following cessation of GHRP-2 dosing occurs over approximately 24-48 hours in rodent pituitary tissue based on receptor binding studies. ^[14]

Peptide Impurity Safety Considerations

For in vivo research use, peptide purity and endotoxin content are critical safety variables. Endotoxin contamination is the most common cause of unexpected inflammatory responses in peptide-treated research animals, and low-purity peptide preparations can introduce structurally related compounds with different pharmacology. Insisting on lot-specific CoA data with endotoxin results below 1 EU/mg for in vivo use is essential. See the supplier verification guide for a structured approach.

How It Compares

GHRP-2 vs. Related GH Secretagogues

Narrative Comparison

GHRP-2 versus GHRP-6. These two hexapeptide GH secretagogues share a common scaffold and historical lineage but differ critically at position 2 (D-βNal in GHRP-2 vs. D-Trp in GHRP-6) and in their receptor selectivity profiles. GHRP-2 is approximately 2-3-fold more potent at GHSR-1a on a molar basis in most published assays, and produces less appetite stimulation due to its lower CD36 affinity. For research designs requiring pure GHSR-1a pharmacology with minimal confounding orexigenic signal, GHRP-2 is the preferred choice. GHRP-6 may be preferred when simultaneous CD36 biology is part of the research question. ^[18]

GHRP-2 versus Ipamorelin. Ipamorelin is a pentapeptide GHSR-1a agonist developed to minimize cortisol and prolactin co-stimulation. Published comparisons show that ipamorelin produces negligible cortisol and prolactin elevation even at maximum stimulatory doses, while GHRP-2 produces measurable, though modest, co-elevations. For research requiring the cleanest possible endocrine selectivity, ipamorelin has an advantage. However, ipamorelin's longer half-life (~2 hours) produces a different GH pulse kinetic profile than GHRP-2's sharp, short pulse, which may be advantageous or disadvantageous depending on the experimental endpoint. ^[20]

GHRP-2 versus Hexarelin. Hexarelin is the most potent GHRP family member at GHSR-1a but also has significant CD36 activity and produces the most pronounced cortisol and prolactin co-elevation. Hexarelin is better suited to experiments requiring maximal receptor activation or studying CD36-mediated effects. GHRP-2 is more appropriate when cortisol confounding would compromise interpretation. ^[9]

GHRP-2 versus MK-677. MK-677 (ibutamoren) is an oral non-peptide GHSR-1a agonist with a ~24-hour half-life, producing sustained GH and IGF-1 elevation rather than pulsatile stimulation. For chronic IGF-1 elevation studies, MK-677 offers convenience via oral dosing. GHRP-2's short half-life and pulsatile GH output more faithfully recapitulate physiological GH secretory patterns, making it preferable for research specifically examining pulsatile GH biology. ^[11]

GHRP-2 versus GHRH analogs (CJC-1295, Sermorelin, Tesamorelin). These compounds act at the GHRH receptor rather than GHSR-1a and represent a mechanistically distinct class. Combined use of GHRP-2 with GHRH analogs produces synergistic GH release, as described above. Research programs comparing GHSR-1a agonism versus GHRH receptor agonism will require both compound classes. GHRP-2 is the most pharmacologically characterized GHSR-1a agonist available in the research peptide market for this purpose.

Where to Buy

Apollo Peptide Sciences supplies this product as GHRP-2 Acetate 10mg at $30.00 per vial. See our full GHRP-2 Acetate 10mg product review for vendor qualification details, CoA verification, and ordering information. The product review page handles outbound affiliate links through the site's standard template.

Before purchasing from any research peptide supplier, researchers should review our supplier verification guide which covers CoA reading, third-party testing services, vendor track records, and regulatory compliance considerations. Key evaluation criteria include:

Purity documentation. The minimum acceptable standard is an HPLC chromatogram with quantified purity (not just a statement), plus mass spectrometry confirmation of molecular weight. Both should be lot-specific, not representative batch data.

Endotoxin testing. For in vivo research use, every lot intended for animal administration should have LAL endotoxin results below 1 EU/mg. Vendors that cannot provide lot-specific endotoxin data should not be used for in vivo protocols.

Physical security and cold-chain. Lyophilized peptides should ship with ice packs to minimize thermal excursions. Vendors with GMP-adjacent manufacturing practices and defined cold-chain logistics are preferable to grey-market sources with unknown handling conditions.

Pricing context. At $3.00/mg, GHRP-2 from Apollo Peptide Sciences is competitively priced within the research peptide market for this compound class. Lower prices from unqualified suppliers may reflect lower purity, higher endotoxin burdens, or misidentified compounds, all of which compromise research validity and increase animal welfare concerns.

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