What is Swiss Chems MK677 Ibutamoren? MK-677, often known as ibutamoren or ibutamoren mesylate, is usually a peptide that belongs to The expansion hormone secretagogues group (GHSR). It works by mimicking the motion of your starvation hormone ghrelin. It binds to at least one of The expansion hormone secretagogue receptors (GHSR) while in the brain