MK-677

MK-677 (ibutamoren) is unusual among growth-hormone secretagogues because it's an orally active, non-peptide molecule. It mimics ghrelin — the 'hunger hormone' — by binding ghrelin's receptor (GHS-R1a) in the brain.

Activating that receptor prompts the pituitary to release more growth hormone, raising both the size of GH pulses and the baseline level, which lifts IGF-1. Because it taps the ghrelin pathway, it also reliably increases appetite. Its big practical distinction is that it can be taken as a once-daily pill, unlike the injectable secretagogues.

The catch is in how it raises GH: chronically and continuously rather than in tight natural pulses. In the year-long trial in older adults it modestly increased lean mass but did not improve strength, and it raised fasting glucose and reduced insulin sensitivity. It is not approved for human use and carries those metabolic trade-offs.