Hexarelin

Hexarelin is the most potent synthetic growth hormone releasing peptide (GHRP) in the hexapeptide class, producing robust GH release through GHS-R1a receptor activation. Its structure incorporates the unusual D-2-methyltryptophan residue, which contributes to its enhanced receptor binding affinity and metabolic stability compared to earlier GHRPs.

Research has demonstrated hexarelin produces the largest GH pulses among synthetic GH secretagogues, though this potency comes with broader hormonal effects including modest elevation of cortisol, prolactin, and ACTH. These secondary effects distinguish it from more selective peptides like ipamorelin.

Unique among GH secretagogues, hexarelin has demonstrated significant cardioprotective properties independent of GH release. Research shows direct cardiac effects mediated through cardiac GHS-R1a receptors, including positive inotropic effects, protection against ischemia-reperfusion injury, and anti-fibrotic activity in cardiac tissue.

However, hexarelin exhibits more pronounced desensitization with repeated dosing compared to other GHRPs, with GH response diminishing significantly over extended administration periods. This property makes it valuable for studying receptor downregulation mechanisms but may limit its utility in chronic research protocols.