Ibutamoren skeletal.svg
Clinical data
Synonyms MK-677; MK-0677; L-163,191; Oratrope
Routes of
By mouth
Legal status
Legal status
Pharmacokinetic data
Elimination half-life 4–6 hours (in beagles);[1]IGF-1 levels remain elevated in humans with a single oral dose for up to 24 hours[2]
CAS Number
PubChem CID
CompTox Dashboard(EPA)
ECHA InfoCard 100.236.734 Edit this at Wikidata
Chemical and physical data
Formula C27H36N4O5S
Molar mass 528.662 g/mol g·mol−1
3D model (JSmol)

Ibutamoren (INN) (developmental code names MK-677MK-0677L-163,191; former tentative brand name Oratrope) is a potent, long-acting, orally-activeselective, 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.[3][4][5][6][7] 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 without affecting cortisol levels.[8]

Ibutamoren has been shown to sustain activation of the GH–IGF-1 axis 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][9][10][11] and human studies have shown it to increase both muscle mass and bone mineral density,[12][13] making it a promising potential therapy for the treatment of frailty in the elderly.[14][15] As of June 2017, ibutamoren is in the preclinical stage of development for growth hormone deficiency.[3]

Since MK-677 is still a Investigational New Drug, it has not yet been approved to be marketed for consumption by humans in the United States.[3] However, it has been used experimentally by some in the bodybuilding community. Since it chemically mimics the hormone ghrelin, it functions as a neuropeptide in the central nervous system and crosses the blood-brain-barrier.[4][5][6][7] According to some recent research and discussion, there is a concern that its particularly longer half-life might over-stimulate the ghrelin receptors in the brain and lead to some harmful mental side effects


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