MK-677 (Ibutamoren)

MK-677 (Ibutamoren) is an orally active, non-peptide ghrelin receptor agonist that mimics ghrelin's action at the pituitary and hypothalamus, stimulating pulsatile GH secretion and raising circulating IGF-1 without requiring injection. Human trials — including studies lasting up to two years — confirm increases in lean body mass, reductions in fat mass, and improvements in sleep architecture (particularly REM and slow-wave sleep), with effects most pronounced in elderly and GH-deficient populations. Tolerability issues include mild fluid retention, increased appetite, and, with prolonged use, elevated fasting glucose and reduced insulin sensitivity due to sustained IGF-1 elevation. It is not FDA-approved and is classified as an investigational new drug; despite its oral convenience, it carries similar long-term concerns to injectable GH secretagogues, including theoretical mitogenic risks from chronically elevated IGF-1.

Evidence last reviewed: 19 Apr 2026