MK-677, also known as Ibutamoren, is a selective agonist of the ghrelin receptor and a growth hormone secretagogue. It is often classified as a growth hormone secretagogue (GHS) or growth hormone secretagogue receptor (GHSR) agonist. This means that it stimulates the secretion of growth hormone (GH) and increases the levels of insulin-like growth factor 1 (IGF-1) in the body.