MK-677 (Ibutamoren)
MK-677 (ibutamoren) is an orally active, non-peptide agonist of the ghrelin receptor that increases growth hormone and IGF-1 levels, is not FDA-approved for any indication, and is taken by mouth rather than injected, distinguishing it from the injectable peptide GH secretagogues.
This page is a research-orientation summary, not a dosing guide. For anything beyond general background, read the primary literature or talk to a qualified clinician — specifics like amount, frequency, or administration aren't something we publish here.
What it does & how it works
MK-677 is a small-molecule (non-peptide) agonist of the growth hormone secretagogue receptor (GHS-R1a), the same receptor activated by endogenous ghrelin, and its oral bioavailability and long plasma half-life (unlike the injectable GHRP peptides) allow it to produce sustained, around-the-clock elevation of growth hormone pulse amplitude rather than a single discrete pulse. Receptor activation in the hypothalamus and pituitary raises GH secretion, which subsequently increases hepatic IGF-1 production, while concurrent ghrelin-receptor activity elsewhere in the body also stimulates appetite.
Typical results seen in research
In a randomized, placebo-controlled trial in healthy older adults, MK-677 significantly increased GH and IGF-1 to levels resembling those of younger adults and increased fat-free mass, but this did not translate into measurable improvements in muscle strength or physical function, and treatment was accompanied by increased fasting glucose, reduced insulin sensitivity, and increased cortisol. Earlier trials found it increased markers of bone turnover and reversed some effects of diet-induced catabolism, but the totality of human evidence indicates metabolic side effects (impaired glucose handling, fluid retention, appetite stimulation) alongside its GH/IGF-1 and body-composition effects, and no trial has established a net clinical benefit sufficient for regulatory approval.
How it’s commonly used
MK-677 is taken orally, as it is absorbed through the gastrointestinal tract unlike the injectable growth hormone secretagogue peptides. It is not FDA-approved for any indication and is studied only in a research/investigational context; it is sold in some markets as an unregulated 'research chemical' outside of approved medical use.
- Annals of Internal Medicine · 2008 Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults: a randomized trial
- Journal of Clinical Endocrinology & Metabolism · 1998 MK-677, an orally active growth hormone secretagogue, reverses diet-induced catabolism
- Journal of Bone and Mineral Research · 1999 Oral administration of the growth hormone secretagogue MK-677 increases markers of bone turnover in healthy and functionally impaired elderly adults. The MK-677 Study Group
- Journal of Clinical Endocrinology & Metabolism · 1997 Oral administration of growth hormone (GH) releasing peptide-mimetic MK-677 stimulates the GH/insulin-like growth factor-I axis in selected GH-deficient adults
Curated from published literature for research orientation. Not an exhaustive review, and not a substitute for reading primary sources.