Evidence-Based Summary
GHRP-2 and GHRP-6 work the same basic way: both activate the growth hormone secretagogue receptor (GHS-R1a, the ghrelin receptor) and cause a short burst of growth hormone (GH) release. Early human work by the compounds' inventor reported that GHRP-2 released GH more effectively than GHRP-6, but that was not a randomized treatment comparison. The clearest human use for either is diagnostic: GHRP-2 (pralmorelin) is approved in Japan as a test for GH deficiency, and GHRP-6 was studied with GHRH as a diagnostic test in a 250-person study. Neither has shown a treatment benefit in a controlled trial; a 2026 Phase 3 stroke trial of a combination product containing GHRP-6 missed its primary endpoint. Both are unapproved in the U.S., both are listed by FDA as compounding substances that may present significant safety risks, and both are banned in sport.
Quick Comparison: GHRP-2 vs GHRP-6
A high-level comparison of molecule class, molecular receptor targets, FDA regulatory approvals, and verified clinical programs.
| Feature | GHRP-2 | GHRP-6 |
|---|---|---|
| Class | Synthetic hexapeptide GH secretagogue (also called pralmorelin, KP-102) | Synthetic hexapeptide GH secretagogue, first described in 1984 |
| Target receptor | GHS-R1a (ghrelin receptor) | GHS-R1a (ghrelin receptor) |
| How it has been given in studies | Single intravenous test administrations; short treatment courses in small studies | Single intravenous test administrations, usually with GHRH; infusion in a combination stroke product |
| Hormones affected besides GH | ACTH and cortisol rise; used in Japan to screen adrenal function | FDA notes possible cortisol effects and reduced insulin sensitivity |
| U.S. regulatory status | Not FDA-approved; FDA 503B category 2 for injectable and nasal routes | Not FDA-approved; FDA 503B category 2 |
| Approval elsewhere | Diagnostic agent in Japan (KEGG lists approval in 2004) | No approved product identified |
| Strongest human evidence | 135-person diagnostic validation study for adult GH deficiency | 250-person diagnostic study (with GHRH); 188-person Phase 3 stroke trial of a combination that missed its endpoint |
| WADA status (2026) | Prohibited at all times, class S2 | Prohibited at all times, class S2 |
Same Receptor, Small Structural Differences
Both peptides belong to the GH-releasing peptide (GHRP) family that led to the discovery of the GH secretagogue receptor in 1996, later found to be the receptor for the stomach hormone ghrelin. This pathway is separate from the GHRH receptor targeted by tesamorelin or sermorelin.
GHRP-2 (pralmorelin)
Primary Target: GHS-R1a (ghrelin receptor)
Affinity Profile: Full GH secretagogue; reported as a more effective GH releaser than GHRP-6 in early human work
Causes a short GH pulse and also raises ACTH and cortisol. Japanese clinicians use that ACTH response to check adrenal function during the same test. Contains a non-natural amino acid (D-2-naphthylalanine), which FDA says complicates quality testing.
GHRP-6
Primary Targets: GHS-R1a (ghrelin receptor)
Affinity Profile: Full GH secretagogue; the first GHRP studied extensively in people
The 1984 discovery work showed GH release from rat pituitary cells and several animal species. Like other GHRPs it can also affect cortisol, and FDA notes reduced insulin sensitivity as a concern.
FDA, International and Anti-Doping Status
United States status checked 11 October 2026. Neither peptide is in an FDA-approved product, and FDA's compounding safety list names both.
GHRP-2 Status & Formulations
Not FDA-approved. FDA placed GHRP-2 for injectable and nasal routes on its list of bulk drug substances that may present significant safety risks (503B, September 29, 2023), citing immunogenicity, impurities, a non-natural amino acid and reports of serious adverse events in study patients, though causality was not established. In Japan, pralmorelin is a diagnostic agent for pituitary GH secretion. WADA class S2.
GHRP-6 Status & Formulations
Not FDA-approved and no approved product identified elsewhere. FDA placed GHRP-6 on its significant-safety-risk list (503B, September 29, 2023), citing possible immunogenicity, impurities, cortisol effects and blood-sugar increases from reduced insulin sensitivity. WADA class S2.
Critical Regulatory Distinction
A diagnostic approval in Japan covers a single test administration under medical supervision; it is not evidence that repeated use is safe or useful. Products sold online as 'research peptides' are not approved medicines.
Diagnostic Tests, Small Treatment Studies and One Failed Phase 3 Trial
Human studies of both peptides mostly measure hormone levels after a single administration. These are useful for diagnosis but do not show that a person feels or functions better.
GHRP-2: Clinical Evidence Overview
GHRP-2's best evidence is diagnostic. A Japanese multicenter study of 135 people (77 healthy adults, 58 with GH deficiency) found much lower GH peaks in GH-deficient patients, with reproducible results. A 2022 study of 36 patients used its ACTH response to help detect adrenal insufficiency. Treatment studies are tiny: six GH-deficient children over eight months had more overnight GH but no rise in IGF-I, and in a 33-man critical-illness study GHRP-2 alone restored GH but did not reduce protein breakdown.
GHRP-6: Clinical Evidence Overview
A 250-person multicenter study (125 adults with pituitary disease, 125 controls) found that GHRH plus GHRP-6 separated GH-deficient adults from healthy people, but GHRP-6 was not tested alone. A nine-man Phase 1 study measured how quickly it leaves the blood. The only large trial, COURAGE-2 (188 adults with acute ischemic stroke in Cuba), tested GHRP-6 combined with epidermal growth factor and did not improve disability, daily function or survival versus standard care.
Curated Clinical Evidence Table
A curated selection of the primary studies behind each compound’s evidence profile. Results from different studies are not directly comparable.
| Study & Citation | Population | Comparison & Dosing | Duration | Main Endpoint | Key Finding | Methodological Limitations |
|---|---|---|---|---|---|---|
| Chihara et al., 2007 (GHRP-2) | 77 healthy adults and 58 with GH deficiency | GHRP-2 test in GH-deficient vs healthy adults | Single test | Peak GH response | GH peaks were far lower in GH deficiency; repeat tests agreed. | Diagnostic accuracy only; says nothing about treatment. |
| Van den Berghe et al., 2002 (GHRP-2) | 33 critically ill men | GHRP-2 alone or with TRH and GnRH vs placebo | 5 days | Hormone and metabolic markers | GHRP-2 restored GH and IGF-I; only the combination reduced protein breakdown. | Small and short; no survival or recovery endpoints. |
| Popovic et al., 2000 (GHRP-6) | 125 adults with pituitary disease and 125 controls | GHRH plus GHRP-6 test | Single test | Diagnostic accuracy for GH deficiency | The combined test separated GH-deficient from healthy adults. | GHRP-6 not tested alone; diagnosis, not treatment. |
| COURAGE-2, Hernández-Bernal et al., 2026 (GHRP-6) | 188 adults with acute ischemic stroke | Epidermal growth factor plus GHRP-6 vs standard care | Acute treatment with follow-up | Disability (primary) | Missed its primary endpoint; a severe-stroke subgroup looked better. | Open-label; combination product; subgroup result needs confirmation; developer-affiliated authors. |
What Is Known About Safety
None of these compounds has the long-term, large-scale safety data that come with an approved medicine. What is known comes from short hormone studies, small trials and FDA's compounding review.
FDA compounding safety listing
FDA lists both GHRP-2 (injectable and nasal routes) and GHRP-6 among bulk drug substances that may present significant safety risks in compounding. For GHRP-2, FDA cites reports of increased insulin needs, deaths of critically ill study subjects, infection and pancreatitis, while noting causality was not established.
| Safety Consideration | GHRP-2 | GHRP-6 |
|---|---|---|
| Non-GH hormone effects | Raises ACTH and cortisol | FDA notes possible cortisol effects |
| Blood sugar | FDA cites increased insulin requirements in reports | FDA cites blood-sugar increases from reduced insulin sensitivity |
| Product quality | Immunogenicity and impurity concerns; non-natural amino acid | Immunogenicity and impurity concerns |
| Long-term human safety data | None beyond small, short studies | None beyond small, short studies |
What GHRP-2 and GHRP-6 Have in Common
Where the two compounds overlap in biology, evidence or regulatory context.
Same receptor and family
Both are synthetic hexapeptides that act on GHS-R1a, the ghrelin receptor, to trigger GH release.
Mainly diagnostic human data
Their strongest human evidence comes from GH stimulation tests, not treatment trials.
Same regulatory picture in the U.S.
Neither is FDA-approved; both are on FDA's compounding safety list and banned in sport (WADA S2).
Key Scientific & Clinical Differences
Meaningful distinctions in mechanism, strength of evidence, safety and regulatory status.
A Japanese diagnostic approval
GHRP-2 (pralmorelin) is a diagnostic agent in Japan. No approved GHRP-6 product was identified.
Reported potency
Early human work reported GHRP-2 as a more effective GH releaser than GHRP-6; this was not a randomized comparison and doesn't show any clinical advantage.
Different late-stage testing
GHRP-6 reached a Phase 3 stroke trial as part of a combination product, which failed its primary endpoint. GHRP-2's treatment studies stayed small.
Scientific Comparison vs Clinical Recommendations
Inside Peptides compares scientific evidence, receptor pharmacology, and official regulatory documents to advance public and professional understanding. We do not determine which compound is appropriate for an individual patient, rank medications with arbitrary scores, or recommend initiating or switching treatments.
Decisions about any medicine require a licensed healthcare professional who can weigh personal medical history, contraindications, interactions and monitoring needs. Unapproved peptides have no established safe use, and products sold as “research chemicals” are not the preparations studied in clinical research.
Approved Uses vs Online Claims
A critical scientific distinction between verified, FDA-approved clinical uses and unverified claims circulating on social media and vendor platforms.
GHRP-2 or GHRP-6 builds muscle or burns fat
Not supportedNeither is FDA-approved; both are on FDA's compounding safety list and prohibited by WADA.
Human studies measured short GH pulses and diagnostic accuracy. No controlled trial has shown muscle gain, fat loss or performance benefit with either peptide.
GHRP-2 is simply a stronger, better GHRP-6
Partly supportedGHRP-2's only approval is diagnostic, in Japan.
Early human work reported stronger GH release with GHRP-2, but a bigger hormone spike is not the same as better outcomes, and the two have never been compared as treatments.
Evidence Strength Across Clinical Domains
Inside Peptides evaluates scientific certainty at the claim level. Because clinical evidence varies significantly depending on the therapeutic endpoint evaluated, each domain is assessed independently.
Diagnosing GH deficiency
GHRP-2 has a 135-person validation study and Japanese diagnostic approval; GHRP-6 was validated only in combination with GHRH.
Any treatment benefit
Small studies show hormone changes; GHRP-6's combination stroke trial missed its endpoint.
Direct comparison between the two
No randomized human study compared GHRP-2 with GHRP-6 for any clinical outcome.
What Research Still Doesn’t Tell Us
Identifying open scientific questions, pending active-comparator trials, and areas where long-term clinical data remain incomplete.
No head-to-head trial
Claims about which is 'better' rest on early potency reports and animal experiments, not controlled comparisons.
Repeated-use safety
There are no long-term human safety studies of either peptide, including effects on blood sugar and cortisol.
Unregulated products
What is sold online may differ in identity, purity and sterility from the material used in published studies.
Related Compound Profiles
Individual profiles provide full molecular datasheets, CAS numbers, preclinical histories, and compound monographs.
Related Educational Resources
Scientific & Regulatory References
Every pharmacological mechanism, clinical trial result, and regulatory approval cited on this page is traceable to official FDA prescribing documentation, ClinicalTrials.gov registries, or peer-reviewed medical publications.
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Diagnostic validation study (human)
A simple diagnostic test using GH-releasing peptide-2 in adult GH deficiency.
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Clinical diagnostic study (human)
Clinical Usefulness of the Growth Hormone-Releasing Peptide-2 Test for Hypothalamic-Pituitary Disorder.
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Uncontrolled treatment study (children)
Effects of eight months treatment with graded doses of a growth hormone (GH)-releasing peptide in GH-deficient children.
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Randomized study (critical illness)
The combined administration of GH-releasing peptide-2 (GHRP-2), TRH and GnRH to men with prolonged critical illness evokes superior endocrine and metabolic effects compared to treatment with GHRP-2 alone.
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Multicenter diagnostic study (human)
GH-releasing hormone and GH-releasing peptide-6 for diagnostic testing in GH-deficient adults.
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Phase 1 pharmacokinetic study
Pharmacokinetic study of Growth Hormone-Releasing Peptide 6 (GHRP-6) in nine male healthy volunteers.
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Phase 3 open-label randomized trial (combination product)
Phase III Open-Label, Randomized Clinical Trial of Epidermal Growth Factor and Growth Hormone Releasing Hexapeptide in Acute Ischemic Stroke.
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Discovery study (animal & in vitro)
On the in vitro and in vivo activity of a new synthetic hexapeptide that acts on the pituitary to specifically release growth hormone.
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Human pharmacology report and overview
GH releasing peptides--structure and kinetics.Reports GHRP-6, GHRP-1 and GHRP-2 as increasingly effective GH releasers in people; not a randomized trial.
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Receptor cloning study
A receptor in pituitary and hypothalamus that functions in growth hormone release.
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FDA compounding safety list
Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety RisksPage content current as of 22 April 2026; checked 11 October 2026.
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Drug database (Japan)
KEGG DRUG D02040: Pralmorelin dihydrochloride (GHRP), Japanese diagnostic agent
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Anti-doping rule
World Anti-Doping Code International Standard: Prohibited List 2026