What is Ghrelin? (Peptide Glossary)

Ghrelin is a 28-amino-acid peptide hormone produced primarily in the stomach, best known as the body's hunger signal - levels rise before meals and fall after eating. Its receptor, the growth hormone secretagogue receptor (GHS-R1a), does double duty: it stimulates appetite and triggers growth hormone release from the pituitary.

The entire GHRP class of research peptides consists of synthetic ghrelin receptor agonists. GHRP-6, GHRP-2, hexarelin, and ipamorelin all activate GHS-R1a, but with different selectivity profiles documented in published research: GHRP-6 strongly stimulates appetite, GHRP-2 is milder, and ipamorelin is the most selective - stimulating GH release in research models with minimal effect on hunger, cortisol, or prolactin.

This selectivity spectrum is why ipamorelin became the dominant research secretagogue despite being neither the strongest nor the cheapest. When comparing suppliers for GHRP-class peptides, note that these are all short, simple hexapeptides or pentapeptides - inexpensive syntheses where quality differences come down to purification and honest filling rather than exotic manufacturing.