MK-677 (Ibutamoren)

An orally active, non-peptide growth hormone secretagogue that mimics ghrelin signaling to increase GH and IGF-1 levels. Though technically not a peptide, it is commonly grouped with GH peptides due to its mechanism and widespread use in the research community.

• Mimics ghrelin by agonizing the GHS-R1a receptor to stimulate pituitary GH release
• Produces sustained GH elevation by activating both hypothalamic and pituitary ghrelin receptors
• Increases appetite through hypothalamic NPY/AgRP signaling pathway
• Does not suppress natural GH pulsatility or HPTA function

• Insulin resistance or type 2 diabetes
• Active malignancy
• Congestive heart failure (fluid retention risk)
• Pregnancy or breastfeeding

Store at room temperature (15–25°C (59–77°F)) in a cool, dry place away from light and moisture. No reconstitution required.

MK-677 has been studied in multiple Phase II trials for muscle wasting, osteoporosis, and GH deficiency. A landmark 2-year study in elderly adults demonstrated sustained increases in GH and IGF-1 without tachyphylaxis, along with improved lean mass. However, concerns about insulin resistance and glucose metabolism have prevented FDA approval to date.