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GHRP-2 and GHRP-6 are the two classic “numbered” growth-hormone-releasing peptides — both hexapeptides on the same ghrelin receptor, one generation apart. GHRP-6 came first and made history; GHRP-2 was tuned from it for more growth hormone and less hunger. Choosing between them is really choosing what you want the ghrelin arm to do.
Research reference only. Not medical advice, prescribing guidance, or a product recommendation.
| Dimension | GHRP-2 | GHRP-6 |
|---|---|---|
| Generation | Second-generation (refined from GHRP-6) | First-generation (the original GHRP) |
| Receptor | GHS-R1a (ghrelin receptor) | GHS-R1a (ghrelin receptor) |
| GH potency | Higher — more GH per dose | Lower than GHRP-2 |
| Appetite stimulation | Modest | Strong — its hallmark effect |
| Cortisol / prolactin | Can rise at higher doses (less selective than ipamorelin) | Can rise (least selective of the family) |
| Regulatory status | Approved in Japan as a GH-deficiency diagnostic (pralmorelin) | None — research compound |
| Historical role | Refined successor | The probe that led to cloning GHS-R1a (1996) and discovering ghrelin (1999) |
| Chain | 6 aa (hexapeptide) | 6 aa (hexapeptide) |
| Molecular weight | 818.0 Da | 873.0 Da |
| FDA approval | None (US) | None |
GHRP-6 is where this entire class begins. Developed out of Cyril Bowers’ work on enkephalin-derived peptides, it was among the first compounds shown to release growth hormone through a receptor separate from GHRH — an orphan receptor whose natural ligand was unknown. GHRP-6 became the pharmacological probe used to find it: the hunt led to cloning the GH-secretagogue receptor (GHS-R1a) in 1996 and, in 1999, to identifying its endogenous ligand, the hunger hormone ghrelin. That lineage is why GHRP-6’s signature effect is appetite — it is, in effect, a synthetic mimic of a hormone discovered only afterward, and it provokes the sharpest hunger of the family.
GHRP-2 (pralmorelin) is the engineered successor. It keeps the same ghrelin-receptor mechanism but was tuned for more growth hormone per dose and markedly less of GHRP-6’s hunger — and it went further than almost any GHRP toward legitimacy, earning approval in Japan as a single-injection diagnostic for pituitary GH reserve. Both remain less selective than ipamorelin, and at higher doses each can nudge cortisol and prolactin. So the practical split is clear: GHRP-2 for a stronger, cleaner GH signal; GHRP-6 when the ghrelin-like appetite effect is itself the point (or the object of study).
GHRP-2 is the more useful GH secretagogue of the two — more potent, much less hunger, and the only one with a regulatory approval anywhere (Japan, as a diagnostic). GHRP-6 is historically the more important molecule, the probe that opened up the ghrelin system, and it remains the reference when the appetite effect matters. Neither is FDA-approved, both are less selective than ipamorelin, and both are commonly studied alongside a GHRH analog for complementary, pulse-preserving release. This page is a research and educational reference.
Both are hexapeptide GHRPs that release growth hormone via the ghrelin receptor. GHRP-2 (pralmorelin) is the more potent, more refined successor — more GH per dose and much less appetite stimulation — and is an approved diagnostic in Japan. GHRP-6 is the original, less potent, and causes the strongest hunger of the family.
GHRP-6, by a wide margin. Its strong, ghrelin-like appetite stimulation is its hallmark effect; GHRP-2 was specifically tuned to release GH with much less of that hunger.
GHRP-6 was the pharmacological probe used to identify the GH-secretagogue receptor (GHS-R1a, cloned 1996) and its natural ligand, ghrelin (1999) — a discovery that reframed GHRP-6 as a synthetic mimic of a hormone found only afterward.
No. GHRP-2 is approved in Japan as a diagnostic (pralmorelin) but not by the FDA; GHRP-6 is a research compound. This page is a research and educational reference.
Mechanism, evidence, and trade-offs between GHRP-2 and GHRP-6 — citation-backed answers grounded in PubMed, PubChem, and ClinicalTrials.gov.