Ibutamoren (INN) (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. It has been shown to increase the secretion of several hormones including GH and insulin-like growth factor 1 (IGF-1) and produces sustained increases in the plasma levels of these hormones while also raising cortisol levels.

Effect on lean mass

Ibutamoren has been shown to sustain activation of the GH–IGF-1 axis, increasing growth hormone secretion by up to 97%, 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, and human studies have shown it to increase both muscle mass and bone mineral density, making it a promising potential therapy for the treatment of frailty in the elderly. As of June 2017, ibutamoren is in the preclinical stage of development for growth hormone deficiency.

Effect on sleep architecture

In a small study of 14 subjects, MK-677 dosed at 25mg/day at bedtime was shown to increase REM sleep by 20% and 50% in young and older subjects respectively. Treatment with MK-677 also resulted in an approximate 50% increase in deep sleep in young subjects.

Growth hormone deficiency

In a study of children with growth hormone deficiency, MK-677 performed better than other growth hormone secretagogues at improving growth hormone levels. An ongoing study compares MK-677 directly to injectable hGH in terms of height velocity in this population.

Non-research use

Since MK-677 is still an Investigational New Drug, it has not yet been approved to be marketed for consumption by humans in the United States. However, it has been used experimentally by some in the bodybuilding community. The use of MK-677 is banned in most sports.