GHRP-2 (pralmorelin) and GHRP-6
First-generation ghrelin-mimetic GH secretagogues
At a glance
What it is: First-generation ghrelin-mimetic GH secretagogues.
Primary research applications:
- Clinical: diagnostic GH stimulation testing (GHRP-2)
- Off-label: GH release for body composition
Editorial summary: GHRP-2 and GHRP-6 are older ghrelin-mimetics that predate ipamorelin. They release GH effectively, but with more off-target effects (cortisol, prolactin, hunger) than ipamorelin, which is why newer use has largely shifted away from them.
What is GHRP-2 / GHRP-6?
GHRP-2 (pralmorelin) and GHRP-6 are hexapeptides developed in the 1980s–1990s as the first practical ghrelin-mimetic GH secretagogues. GHRP-2 has some regulatory history as a GH stimulation test (approved in Japan as GHRP Kaken for diagnostic use).[1]
Mechanism of action
Both bind the GHS-R1a (ghrelin) receptor to stimulate GH release. GHRP-6 is notable for strong appetite stimulation through the same receptor's effects on hunger circuits. GHRP-2 is somewhat cleaner but both can elevate cortisol and prolactin.
What the research shows
The peer-reviewed literature on GHRP-2 / GHRP-6 is summarized below across two tiers: human research (the highest standard), and preclinical / emerging research (animal models and early-stage human work).
Claims and the evidence behind them
This table summarizes commonly discussed claims and how the published evidence weighs in. The aim is clarity — supported claims, claims that look promising but need more data, and claims that outrun the science.
| Claim | What the evidence shows | Verdict |
|---|---|---|
| Releases GH reliably in humans | Supported | Supported |
| Causes significant hunger (GHRP-6) | Yes, as expected from ghrelin mechanism | Supported |
| Is as clean as ipamorelin | No — cortisol and prolactin elevations are more prominent | Unsupported |
| Effective for body composition in healthy adults | No RCT evidence | Preliminary |
Reported user experiences
How the research describes administration
Subcutaneous injection. Used historically in research and diagnostic protocols.
Editorial note
Administration details above describe how the peptide is given in published studies. We summarize this for educational completeness — these descriptions are not protocols, dosing recommendations, or instructions for personal use. Decisions about treatment require an appropriately licensed clinician.
Safety considerations and open questions
The takeaway
Older, somewhat messier cousins of ipamorelin. Useful in historical context — they proved the ghrelin receptor strategy works — but there's little reason to prefer them over ipamorelin for the off-label uses common today.
Frequently asked questions
What's the difference between GHRP-2 and GHRP-6?
Both are ghrelin-receptor agonists. GHRP-6 strongly stimulates appetite (an advantage in bulking, a disadvantage otherwise). GHRP-2 has less appetite effect but more cortisol/prolactin elevation.
Is GHRP-2 approved anywhere?
Yes — it's approved in Japan as a diagnostic agent (GHRP Kaken) for growth hormone stimulation testing.
Why would I choose GHRP-2 over ipamorelin?
Generally you wouldn't. Ipamorelin has a cleaner side-effect profile and produces GH release without the cortisol/prolactin penalty.
References
- 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):975-82. https://pubmed.ncbi.nlm.nih.gov/2108187/
- Chihara K, Shimatsu A, Hizuka N, et al. A simple diagnostic test using GH-releasing peptide-2 in adult GH deficiency. Eur J Endocrinol. 2007;157(1):19-27. https://pubmed.ncbi.nlm.nih.gov/17609398/