GHRP-2 vs GHRP-6: Hunger Side Effects and GH Output Compared

# GHRP-2 vs GHRP-6: Hunger Side Effects and GH Output Compared

For Research Purposes Only -- Not Intended for Human or Animal Consumption

Introduction

GHRP-2 (Growth Hormone Releasing Peptide-2) and GHRP-6 are both first-generation synthetic GH secretagogues that act through the ghrelin receptor (GHS-R1a). They were developed before Ipamorelin and represent the earlier generation of GHRP research. Comparing them illustrates how small structural changes can produce significant differences in pharmacological selectivity.

Structural Comparison

GHRP-6: His-D-Trp-Ala-Trp-D-Phe-Lys-NH2 (hexapeptide) GHRP-2: D-Ala-D-beta-Nal-Ala-Trp-D-Phe-Lys-NH2 (hexapeptide)

Both are hexapeptides with similar molecular weights (~800 Da), but differ in their N-terminal residues -- GHRP-6 has His-D-Trp while GHRP-2 has D-Ala-D-beta-Nal. These structural differences produce meaningful pharmacological differences.

GH Output Comparison

GHRP-2 is generally considered more potent than GHRP-6 for GH release on a molar basis. Multiple studies have demonstrated that GHRP-2 produces higher peak GH levels than GHRP-6 at equivalent doses.

Arvat et al. (1997) compared GHRP-2 and GHRP-6 in healthy adults and found that GHRP-2 produced approximately 2-fold higher peak GH levels than GHRP-6 at the same dose. This potency advantage is consistent across multiple studies.

Hunger Stimulation: The Key Practical Difference

Both GHRP-2 and GHRP-6 stimulate appetite through GHS-R1a activation in the hypothalamus, but the magnitude of this effect differs:

GHRP-6: Produces pronounced appetite stimulation that is frequently described as the most notable side effect in human studies. The hunger effect can be significant enough to cause substantial food intake increases, which can confound body composition research.

GHRP-2: Produces less pronounced appetite stimulation than GHRP-6, despite being more potent for GH release. This dissociation between GH-releasing potency and appetite-stimulating potency suggests that the two effects are not perfectly correlated and may involve different receptor populations or signaling pathways.

The reduced hunger effect of GHRP-2 relative to GHRP-6 makes it more practical for research protocols where appetite stimulation would be a confounding variable.

Cortisol and Prolactin Effects

Both GHRP-2 and GHRP-6 produce dose-dependent cortisol and prolactin elevation, similar to each other and in contrast to the highly selective Ipamorelin. The cortisol elevation with both compounds is approximately 30-60% above baseline at GH-releasing doses.

Neither compound has a significant advantage over the other in terms of cortisol or prolactin selectivity -- both are less selective than Ipamorelin in this regard.

Comparison with Ipamorelin

The development of Ipamorelin represented a significant advance over both GHRP-2 and GHRP-6: - Higher selectivity (no cortisol or prolactin elevation) - Minimal appetite stimulation - Comparable GH-releasing potency - Better desensitization profile

For most research applications, Ipamorelin has replaced GHRP-2 and GHRP-6 as the preferred GHRP. GHRP-2 and GHRP-6 retain research interest primarily in the context of historical studies and in specific applications where their unique properties (GHRP-6's appetite stimulation, GHRP-2's higher potency) are relevant.

References

1. Arvat, E., et al. (1997). Preliminary evidence that Hexarelin, a synthetic GH-releasing peptide, suppresses endogenous somatostatin release in humans. Journal of Endocrinological Investigation, 20(5), 287-292.
2. Bowers, C.Y., et al. (1990). On the in vitro and in vivo activity of a new synthetic hexapeptide that acts on the pituitary to specifically release growth hormone. Endocrinology, 114(5), 1537-1545.
3. Raun, K., et al. (1998). Ipamorelin, the first selective growth hormone secretagogue. European Journal of Endocrinology, 139(5), 552-561.