The GHRP Family
Growth Hormone Releasing Peptides (GHRPs) are a class of compounds that stimulate GH release through the Ghrelin receptor (GHSR). GHRP-2, GHRP-6, and Ipamorelin are all members of this class but differ significantly in their selectivity and side effect profiles.
GHRP-2 and GHRP-6: The Older Compounds
GHRP-2 and GHRP-6 were developed before Ipamorelin and both produce meaningful GH stimulation. However, they also significantly stimulate cortisol and prolactin release through off-target receptor activity. GHRP-6 additionally stimulates appetite strongly — useful for some applications, problematic for others. These off-target effects limit their utility in general GH optimization protocols.
Ipamorelin: Selectivity Is the Key Advantage
Ipamorelin was specifically developed to maximize GH stimulation while minimizing cortisol and prolactin stimulation. Animal studies confirm that Ipamorelin produces robust GH release with significantly less cortisol and prolactin stimulation than GHRP-2 or GHRP-6. This selectivity is the primary reason physicians designing GH optimization protocols typically prefer Ipamorelin.
Practical Implication
When a physician designs a GH optimization protocol, the goal is to raise GH and IGF-1 toward upper-normal ranges without unwanted hormonal side effects. Ipamorelin’s selectivity makes it easier to achieve this goal cleanly. When combined with CJC-1295 (which acts on a different receptor — GHRH-R rather than GHSR), the two compounds provide complementary, additive GH stimulation through independent pathways.