GHRP-6 vs GHRP-2

GHRP-6 and GHRP-2 are different six-residue peptides that stimulate growth hormone through the ghrelin-receptor system. Controlled GHRP-2 meal studies found greater food intake, while GHRP-6 has direct human peptide measurements and detailed endocrine experiments. These sources do not establish which produces more muscle, better recovery or a stronger appetite effect in a direct comparison.

Research reviewed October 15, 2026. Educational information only.

Two different peptides acting on a shared hormone system

GHRP-6 and GHRP-2 are synthetic peptides containing six amino acids with different amino-acid structures. GHRP-2 is also called pralmorelin or KP-102; the Japanese pharmaceutical dossier identifies pralmorelin dihydrochloride as the diagnostic preparation. Neither name describes natural ghrelin, even though both belong to the group of compounds that activate the ghrelin-receptor system.

That receptor system influences growth hormone secretion and appetite. Growth hormone-releasing hormone, or GHRH, supplies another input to the pituitary through a different receptor. A secretagogue is a substance that stimulates secretion. Its response depends on the pituitary’s ability to release growth hormone and on other hormone signals. A larger hormone pulse is a measurement of secretion, whose clinical significance depends on what happens to symptoms, function and harms.

The main differences

What hormone-release experiments establish

Bowers and colleagues studied eighteen healthy men with intravenous GHRP-6, placebo, GHRH and selected combined conditions. Growth hormone rose with increasing GHRP-6 exposure. At submaximal conditions, combining GHRP-6 with GHRH produced a response greater than the sum expected from the individual stimuli. Prolactin and cortisol also rose about twofold in one condition, showing that the measured response extended beyond growth hormone.

In a separate experiment in nine healthy men, blocking GHRH reduced the maximum growth hormone rise after GHRP-6 from 33.8 ± 4.8 to 6.2 ± 1.8 micrograms/L, reported as means ± standard error. This experiment identifies a contribution from the body’s own GHRH. It does not test whether a combination improves strength or recovery.

GHRP-2 has also been studied as a supervised stimulation test. Chihara and colleagues compared seventy-seven healthy participants with fifty-eight patients whose insulin-tolerance tests showed low growth hormone release. The GHRP-2 test separated the groups, with interpretation dependent on the hormone assay. That diagnostic result addresses the ability to release growth hormone rather than a benefit from chronic exposure. The studies summarized here do not randomly compare GHRP-6 and GHRP-2 for a sustained functional outcome.

The measured human appetite evidence

Laferrère and colleagues compared GHRP-2 with saline during separate controlled visits in seven lean healthy men. The men received an infusion under the skin and later ate freely from a buffet meal. They ate an average 35.9% more during GHRP-2 exposure, and every participant increased intake. This establishes an acute eating response; it does not tell us how body weight, nutrition or physical function would change over months.

A second crossover study enrolled ten lean and nine obese adults, all healthy and weight-stable. During two GHRP-2 conditions, food intake increased by 10.2% and 33.5% relative to placebo. Obesity status did not establish a different intake response. Those measurements are useful because they concern food actually eaten, beyond a subjective report of hunger.

An assertion that GHRP-6 causes more hunger than GHRP-2 would require an appropriate direct comparison. The meal experiments cited here tested GHRP-2 against saline or placebo, with no GHRP-6 arm. They cannot provide that ranking, regardless of how commonly the ranking appears in product descriptions.

Pharmacokinetics: the peptide in blood and the hormone it releases

Cabrales and colleagues measured GHRP-6 itself in nine healthy men after injection into a vein. The plasma profile contained an early distribution phase and a later terminal decline, with mean half-lives of 7.6 ± 1.9 minutes and 2.5 ± 1.1 hours across the three studied exposure levels. The abstract does not state whether the accompanying variation is a standard deviation or standard error. Four participants had temporary concentration spikes during elimination.

A growth hormone curve measures a released hormone, not necessarily the secretagogue that caused its release. The GHRP-2 appetite and stimulation studies do not supply an equivalent intact-peptide human elimination estimate. The cited record therefore supports a route-specific GHRP-6 measurement, while leaving a matched exposure comparison with GHRP-2 unresolved. Half-life alone would not rank effects on appetite, muscle or recovery.

A later GHRP-6 combination trial asks a different question

The human literature is broader than acute hormone testing. In the 2026 COURAGE-2 stroke report, 188 adults were randomized to epidermal growth factor plus GHRP-6 with standard care, or standard care alone. The study was open-label and followed disability, daily activities and survival. It did not establish an overall improvement in these measures and missed its primary outcome; the published abstract does not report the overall disability values for each group.

Among twenty-seven participants with more severe strokes, the combination group had lower disability scores at six months: 2.6 versus 4.7 on a scale running from no symptoms to death (reported intervals 1.3–3.8 and 2.6–6.0; P=0.03). The small subgroup signal does not replace the overall trial result. Because the study combined two active agents and had no GHRP-2 arm, it cannot isolate a GHRP-6 effect or settle this comparison. The published abstract does not say whether the subgroup analysis was planned before the trial.

Safety depends on the actual preparation and setting

FDA identifies possible immune reactions to aggregated peptide or related impurities in compounded GHRP-2 and GHRP-6 preparations. For GHRP-6, the agency also describes cortisol and blood-glucose concerns associated with reduced insulin sensitivity. For GHRP-2, it lists reports including increased insulin requirements, infection, pancreatitis and deaths in critically ill study participants, while explicitly stating that causality has not been established. These reports do not support a simple relative-safety ranking.

The stroke combination trial also warrants care in interpreting adverse events. Severe events occurred in 30 of 95 combination recipients and 18 of 93 standard-care patients, an odds ratio of 1.92 with a 95% confidence interval of 0.981–3.767. The observed rate was higher with the combination, but the interval leaves the size and existence of a treatment effect uncertain. The authors judged none treatment-related. Neither their attribution nor the uncertain comparison establishes the safety of isolated GHRP-6 or a different product.

Short monitored physiology studies and a diagnostic pharmaceutical preparation answer narrower questions than prolonged use of an unapproved product. The Japanese pralmorelin dossier should be read in its diagnostic context; its existence does not establish an FDA-approved GHRP-2 treatment or make another supplied preparation equivalent.

Frequently asked questions

Profiles and related reading

References

1. 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. The Journal of clinical endocrinology and metabolism. 1990;70(4):975–982. DOI: 10.1210/jcem-70-4-975.

   In eighteen healthy men, GHRP-6 increased growth hormone, some combinations with GHRH produced a greater-than-additive response, and prolactin and cortisol rose in one condition.

2. Pandya N, DeMott-Friberg R, Bowers CY, Barkan AL, Jaffe CA. Growth hormone (GH)-releasing peptide-6 requires endogenous hypothalamic GH-releasing hormone for maximal GH stimulation. The Journal of clinical endocrinology and metabolism. 1998;83(4):1186–1189. DOI: 10.1210/jcem.83.4.4711.

   In nine healthy men, blocking the body’s own GHRH greatly reduced the growth hormone rise after GHRP-6.

3. Doi N, Hirotani C, Ukai K, Shimada O, Okuno T, Kurasaki S, Kiyofuji T, Ikegami R, Futamata M, Nakagawa T, Ase K, Chihara K. Pharmacological characteristics of KP-102 (GHRP-2), a potent growth hormone-releasing peptide. Arzneimittelforschung. 2004;54(12):857–867. DOI: 10.1055/s-0031-1297041.

   The original pharmacology paper identifies the modified peptide and dihydrochloride preparation.

4. Chihara K, Shimatsu A, Hizuka N, Tanaka T, Seino Y, Kato Y; KP-102 Study Group. A simple diagnostic test using GH-releasing peptide-2 in adult GH deficiency. European Journal of Endocrinology. 2007;157(1):19–27. DOI: 10.1530/EJE-07-0066.

   The diagnostic comparison reports reproducibility and calibration-dependent interpretation of provoked GH.

5. Laferrère B, Abraham C, Russell CD, Bowers CY. Growth hormone releasing peptide-2 (GHRP-2), like ghrelin, increases food intake in healthy men. The Journal of clinical endocrinology and metabolism. 2005;90(2):611–614. DOI: 10.1210/jc.2004-1719.

   Seven healthy men received subcutaneous GHRP-2 infusion and saline on separate visits. Investigators weighed buffet food consumed; participants ate more during GHRP-2 exposure.

6. Laferrère B, Hart AB, Bowers CY. Obese subjects respond to the stimulatory effect of the ghrelin agonist growth hormone-releasing peptide-2 on food intake. Obesity (Silver Spring, Md.). 2006;14(6):1056–1063. DOI: 10.1038/oby.2006.121.

   A larger crossover meal study found dose-dependent intake responses in lean and obese participants.

7. Cabrales A, Gil J, Fernández E, Valenzuela C, Hernández F, García I, Hernández A, Besada V, Reyes O, Padrón G, Berlanga J, Guillén G, González LJ. Pharmacokinetic study of Growth Hormone-Releasing Peptide 6 (GHRP-6) in nine male healthy volunteers. European journal of pharmaceutical sciences : official journal of the European Federation for Pharmaceutical Sciences. 2013;48(1-2):40–46. DOI: 10.1016/j.ejps.2012.10.006.

   A peptide-specific assay followed GHRP-6 in plasma after IV administration to nine healthy men. Concentrations had an early decline and a later elimination phase, with temporary rises during elimination in four participants.

8. Raun K, Hansen BS, Johansen NL, Thøgersen H, Madsen K, Ankersen M, Andersen PH. Ipamorelin, the first selective growth hormone secretagogue. European journal of endocrinology. 1998;139(5):552–561. DOI: 10.1530/eje.0.1390552.

   An animal comparator study records accompanying ACTH and cortisol responses to GHRP-2.

9. Pharmaceuticals and Medical Devices Agency. Pralmorelin hydrochloride / GHRP Kaken 100 application dossier. 2004. Japanese regulatory document.

   The dossier specifies the dihydrochloride chemistry and diagnostic purpose.

10. U.S. Food and Drug Administration. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks. Agency safety assessment; accessed 2026-10-13.

    The agency identifies substance- and route-specific safety concerns and gaps for compounded peptides.

11. Hernández-Bernal F, Subirós-Martínez N, Gutiérrez-Ronquillo JH, et al. Phase III Open-Label, Randomized Clinical Trial of Epidermal Growth Factor and Growth Hormone Releasing Hexapeptide in Acute Ischemic Stroke. Journal of Clinical Neuroscience. 2026;152:112195. doi:10.1016/j.jocn.2026.112195. PMID:42462342.

    The later stroke trial tested EGF plus GHRP-6, missed its primary outcome and reported a subgroup signal; it cannot isolate GHRP-6 or rank it against GHRP-2.