Ghrelin is an orexigenic peptide hormone mainly produced in the stomach as precursor preproghrelin. Cleavage of preproghrelin followed by modification leads to the formation of ghrelin with the addition of a fatty acid to its serine 3 residue; ghrelin is capable of activating the growth hormone release receptor (GHSR). Ghrelin is involved in appetite stimulation and growth hormone release.

Most circulating ghrelin is in the non-acylated form (des-octanoyl) ghrelin. (Des-octanoyl)-ghrelin has some distinct functions from ghrelin, the lack of acylation prevents binding to the ghrelin receptor and growth hormone release. However, (des-octanoyl) ghrelin has negative inotropic effects on papillary muscle and cardioprotective function. There is evidence (des-octanoyl) ghrelin inhibits proliferation of certain cancer cell lines, while promoting adipogenesis has been observed in other experiments in vivo.