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