GHRP-6 was one of the first growth hormone releasing peptides discovered. It effectively stimulates GH release — but it also raises cortisol (stress hormone), prolactin (reproductive hormone), and aldosterone (blood pressure regulator), and produces intense hunger (ghrelin-like appetite stimulation).¹

For researchers, these off-target effects create experimental noise. If you treat an animal with GHRP-6 and observe metabolic changes, you can't determine whether those changes came from GH, cortisol, prolactin, or the altered feeding behavior. The compound answers your question while simultaneously introducing new confounders.

Ipamorelin's selectivity was demonstrated in a definitive 1998 study by Raun et al. At doses producing equivalent GH release to GHRP-6, Ipamorelin showed no statistically significant elevation of cortisol, prolactin, or aldosterone. Even at supraphysiological doses (far above those needed for GH release), off-target hormone changes remained minimal.²

This selectivity revolutionized GH secretagogue research. For the first time, researchers had a tool that could stimulate GH without confounding hormonal changes — allowing cleaner experimental designs and more interpretable results.

The OSYRIS catalog prioritizes research tools that produce interpretable results. Ipamorelin's selectivity makes it the superior research tool for any protocol where GH-specific effects are the question. GHRP-6's historical value was establishing that GH secretagogues were possible. Ipamorelin's value is showing that they can be selective.

Researchers who specifically need to study the multi-hormonal effects of non-selective GHS-R1a activation (the cortisol + prolactin + appetite changes alongside GH) would need GHRP-6. But for the vast majority of GH research, Ipamorelin's clean profile is preferred.