Growth Hormone · Body Composition · Bone Health
MK-677 (Ibutamoren)
Also known as: Ibutamoren, Ibutamoren mesylate, L-163,191
An orally active non-peptide ghrelin receptor agonist studied in Phase 2 trials for frailty, hip fracture recovery, and growth hormone deficiency.
Sign in to add to watchlistEvidence strength
Strength of human clinical evidence — A (strongest) to D (mostly preclinical). This reflects research maturity, not safety or suitability.
Vial Theory provides educational research summaries only. Content is not medical advice, diagnosis, treatment, dosing guidance, or individualized suitability screening. Regulatory status can change over time and varies by jurisdiction.
Key Takeaways
- ›MK-677 (ibutamoren) is an orally active, non-peptide ghrelin-receptor agonist that raises growth hormone and IGF-1.
- ›Phase 2 trials showed increased lean mass but not consistent strength gains, and development was discontinued.
- ›It can raise fasting glucose and HbA1c, a notable insulin-sensitivity concern.
- ›It is not approved, is on the WADA prohibited list, and long-term safety is uncharacterized.
- ›Claims exceed the evidence. Speak with a licensed healthcare professional before any health decisions.
What It Is
MK-677 (ibutamoren) is a small-molecule, orally bioavailable, non-peptide agonist of the growth hormone secretagogue receptor (GHSR-1a), the same receptor targeted endogenously by ghrelin. Unlike peptide GHRH analogs, MK-677 is not a peptide and survives oral administration, and its plasma half-life supports once-daily exposure.
It was developed by Merck Research Laboratories during a broader medicinal-chemistry program around growth hormone secretagogues. Mechanistically, GHSR-1a activation in the pituitary and hypothalamus produces pulsatile growth hormone release and downstream IGF-1 elevation; the receptor is also expressed in central appetite circuits, which contributes to the increased food intake commonly reported with the compound.
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Disclaimer: This content is for educational and research purposes only and is not medical advice. Always consult a licensed healthcare professional before making health-related decisions.