Evidence-Based Summary
GHRP-6 and ipamorelin both release growth hormone by activating the ghrelin receptor (GHS-R1a). The main difference is selectivity. In Novo Nordisk's 1998 animal experiments, ipamorelin released about as much GH as GHRP-6, but unlike GHRP-6 and GHRP-2 it did not raise ACTH or cortisol in swine. That selectivity was shown in animals; we found no published human study that directly compared the two. In people, ipamorelin's main efficacy trial (a Phase 2 study in 114 bowel-surgery patients) found no significant benefit for recovery of gut function, and GHRP-6's main trial (a Phase 3 stroke trial of a combination product) missed its primary endpoint. Neither is FDA-approved, both are on FDA's compounding safety list, and both are banned in sport.
Quick Comparison: GHRP-6 vs Ipamorelin
A high-level comparison of molecule class, molecular receptor targets, FDA regulatory approvals, and verified clinical programs.
| Feature | GHRP-6 | Ipamorelin |
|---|---|---|
| Class | First-generation synthetic hexapeptide GHRP (1984) | Synthetic pentapeptide GH secretagogue (Novo Nordisk, 1998) |
| Target receptor | GHS-R1a (ghrelin receptor) | GHS-R1a (ghrelin receptor) |
| Selectivity | Raised ACTH and cortisol in swine; FDA notes possible cortisol effects | Did not raise ACTH or cortisol above GHRH levels in swine (animal finding) |
| How it has been given in studies | Single intravenous test administrations; infusion in a combination stroke product | Intravenous infusions in human pharmacology and bowel-surgery trials |
| U.S. regulatory status | Not FDA-approved; FDA 503B category 2 | Not FDA-approved; FDA 503B category 2 |
| Strongest human evidence | Diagnostic study with GHRH; Phase 3 combination stroke trial missed its endpoint | Phase 2 bowel-surgery RCT (114 patients) missed its efficacy endpoint |
| Main safety concerns | Cortisol and blood-sugar effects; immunogenicity and impurities | FDA cites serious adverse events including death with intravenous use; immunogenicity and impurities |
| WADA status (2026) | Prohibited at all times, class S2 | Prohibited at all times, class S2 |
Same Receptor, Different Hormone Side-Effects
Both peptides activate the GH secretagogue receptor, later identified as the ghrelin receptor. Ipamorelin was built from the GHRP-1 structure without its central Ala-Trp pair, and its developers reported it as the first selective GH secretagogue.
GHRP-6
Primary Target: GHS-R1a (ghrelin receptor)
Affinity Profile: Full GH secretagogue; also stimulates ACTH and cortisol
Releases GH directly from pituitary cells and acts in the hypothalamus. In the 1998 swine experiments it raised ACTH and cortisol, and FDA notes cortisol and blood-sugar concerns.
Ipamorelin
Primary Targets: GHS-R1a (ghrelin receptor)
Affinity Profile: GH release similar to GHRP-6 in rat and swine experiments, with little ACTH or cortisol effect
In swine, ACTH and cortisol stayed at levels seen after GHRH even at very high doses relative to the GH-releasing dose. This selectivity is an animal finding; a human study confirmed a single short GH pulse but did not compare it with GHRP-6.
FDA, Development History and Anti-Doping Status
United States status checked 11 October 2026. Both peptides are named on FDA's list of bulk drug substances that may present significant safety risks in compounding.
GHRP-6 Status & Formulations
Not FDA-approved. FDA 503B category 2 since September 29, 2023, citing possible immunogenicity, impurities, cortisol effects and blood-sugar increases from reduced insulin sensitivity. WADA class S2.
Ipamorelin Status & Formulations
Not FDA-approved. FDA 503B category 2 since September 29, 2023. FDA cites immunogenicity and impurity concerns, non-natural amino acids, and a published report of serious adverse events including death when ipamorelin was given intravenously for gut motility. Two Phase 2 bowel-surgery trials sponsored by Helsinn Therapeutics are listed as completed; no approval followed. WADA class S2.
Critical Regulatory Distinction
Being studied in a regulated trial is not approval. Products sold online as 'research peptides' are not approved medicines and are not the material used in the published trials.
Hormone Studies and Two Negative Larger Trials
Each peptide has a handful of human studies. The larger trials tested specific clinical uses (stroke recovery, gut recovery after surgery) and neither succeeded.
GHRP-6: Clinical Evidence Overview
A 250-person multicenter study showed that GHRH plus GHRP-6 could diagnose adult GH deficiency, but GHRP-6 was not tested alone. A nine-man Phase 1 study described its pharmacokinetics. COURAGE-2, a Phase 3 open-label trial in 188 stroke patients, combined GHRP-6 with epidermal growth factor and did not improve disability, daily function or survival versus standard care.
Ipamorelin: Clinical Evidence Overview
A human pharmacology study in healthy men (eight per dose level) found a single GH pulse after each intravenous infusion, with a short half-life of about two hours. In a Phase 2 double-blind trial of 114 bowel-resection patients, ipamorelin was well tolerated, but time to first tolerated meal (25.3 vs 32.6 hours) did not differ significantly from placebo. A larger second Phase 2 trial (320 enrolled, registry record in References) is listed as completed with no posted results.
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 |
|---|---|---|---|---|---|---|
| Raun et al., 1998 (direct animal comparison) | Rat pituitary cells, anaesthetised rats, conscious swine | Ipamorelin vs GHRP-6 and GHRP-2 | Acute experiments | GH, ACTH and cortisol release | Similar GH release to GHRP-6; only GHRP-6 and GHRP-2 raised ACTH and cortisol. | Animal data from the developer; not confirmed head-to-head in people. |
| Gobburu et al., 1999 (ipamorelin) | Healthy male volunteers, eight per dose level | Escalating intravenous infusions | Single administrations | Pharmacokinetics and GH response | Single GH pulse at every level; half-life about 2 hours. | Pharmacology only; no comparison with GHRP-6 and no clinical endpoint. |
| Beck et al., 2014 (ipamorelin, NCT00672074) | 114 adults after bowel resection | Ipamorelin vs placebo | Up to 7 days | Time to first tolerated solid meal | 25.3 vs 32.6 hours; not significant (p = 0.15). | Small proof-of-concept trial with mixed underlying conditions. |
| Popovic et al., 2000 (GHRP-6) | 125 adults with pituitary disease and 125 controls | GHRH plus GHRP-6 test | Single test | Diagnostic accuracy | Combined test separated GH-deficient from healthy adults. | GHRP-6 not tested alone. |
| 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. | Open-label; combination product; 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.
Both are on FDA's compounding safety list
FDA lists GHRP-6 and ipamorelin acetate among bulk substances that may present significant safety risks. For ipamorelin, FDA points to a published report of serious adverse events, including death, with intravenous use for gut motility, and says it lacks safety information for other injectable routes.
| Safety Consideration | GHRP-6 | Ipamorelin |
|---|---|---|
| Cortisol / ACTH | Raised in animal studies; FDA notes possible cortisol effects | Not raised in swine; human confirmation limited |
| Blood sugar | FDA cites reduced insulin sensitivity | No specific FDA statement |
| Trial tolerability | No side effects reported in the 250-person diagnostic study | Adverse events similar to placebo in the 114-patient Phase 2 trial (87.5% vs 94.8%) |
| Product quality | Immunogenicity and impurity concerns | Immunogenicity and impurity concerns; non-natural amino acids |
What GHRP-6 and Ipamorelin Have in Common
Where the two compounds overlap in biology, evidence or regulatory context.
Ghrelin-receptor agonists
Both release GH through GHS-R1a rather than the GHRH receptor.
No proven treatment use
Each compound's main efficacy trial missed its primary endpoint.
Same regulatory status
Not FDA-approved, on FDA's 503B safety list, and prohibited by WADA (S2).
Key Scientific & Clinical Differences
Meaningful distinctions in mechanism, strength of evidence, safety and regulatory status.
Selectivity
In animal experiments ipamorelin released GH without raising ACTH or cortisol; GHRP-6 raised both.
Structure
GHRP-6 is a hexapeptide; ipamorelin is a pentapeptide with non-natural amino acids.
Clinical targets tested
GHRP-6 was tested in diagnostic GH testing and stroke; ipamorelin in recovery of gut function after bowel surgery.
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.
Ipamorelin is the 'clean' GHRP with no side effects
Partly supportedNot FDA-approved; on FDA's compounding safety list.
Its selectivity for GH over cortisol was shown mainly in swine. That is not the same as having no side effects, and FDA cites serious adverse events with intravenous use.
Either peptide builds muscle, burns fat or slows aging
Not supportedBoth prohibited in sport (WADA S2).
No controlled human trial has tested body composition, performance or aging outcomes for either peptide.
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.
Acute GH release in people
Both reliably cause a short GH pulse in small human studies.
Selectivity (sparing cortisol)
The direct comparison comes from developer animal experiments.
Any clinical treatment benefit
GHRP-6's combination stroke trial and ipamorelin's Phase 2 gut-recovery trial both missed their primary endpoints.
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 human head-to-head study
Selectivity differences have not been confirmed in a direct human comparison.
Unpublished trial
Ipamorelin's larger Phase 2 trial (320 enrolled) has no posted results or matching publication that we could find.
Long-term safety
There are no long-term human safety data for repeated use of either peptide.
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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Discovery pharmacology (rat cells, rats, swine)
Ipamorelin, the first selective growth hormone secretagogue.Animal and cell work by Novo Nordisk scientists; compares ipamorelin with GHRP-6 and GHRP-2 in the same experiments.
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Human pharmacokinetic/pharmacodynamic study
Pharmacokinetic-pharmacodynamic modeling of ipamorelin, a growth hormone releasing peptide, in human volunteers.
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Phase 2 randomized placebo-controlled trial
Prospective, randomized, controlled, proof-of-concept study of the Ghrelin mimetic ipamorelin for the management of postoperative ileus in bowel resection patients.Sponsored by Helsinn Therapeutics; see the trial registry record in References.
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Trial registry record
Safety and Efficacy of Ipamorelin for Management of Post-Operative IleusPhase 2; Completed; 117 enrolled (actual); no results posted on the registry. Checked 11 October 2026.
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Trial registry record
Safety and Efficacy of Ipamorelin Compared to Placebo for the Recovery of Gastrointestinal FunctionPhase 2; Completed; 320 enrolled (actual); no results posted on the registry and no matching publication found. Checked 11 October 2026.
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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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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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Anti-doping rule
World Anti-Doping Code International Standard: Prohibited List 2026