Ibutamoren (INNTooltip International Nonproprietary Name) (developmental code names MK-677, MK-0677, LUM-201, L-163,191; former tentative brand name Oratrope) is a potent, long-acting, orally-active, selective, and non-peptide agonist of the ghrelin receptor and a growth hormone secretagogue, mimicking the growth hormone (GH)-stimulating action of the endogenous hormone ghrelin.

[8] Ibutamoren has been shown to sustain activation of the GH–IGF-1 axis, increasing growth hormone secretion by up to 97%,[9] and to increase lean body mass with no change in total fat mass or visceral fat.

It is under investigation as a potential treatment for reduced levels of these hormones, such as in children or elderly adults with growth hormone deficiency,[3][10][11][12] and human studies have shown it to increase both muscle mass and bone mineral density,[13][14] making it a promising potential therapy for the treatment of frailty in the elderly.

[15][16] As of June 2017, ibutamoren is in the preclinical stage of development for growth hormone deficiency.

[18] An ongoing study compares MK-677 directly to injectable hGH in terms of height velocity in this population.