MK-677 is a nonpeptide, spiro piperidine sulfonamide reported functionally indistinguishable in vitro and in vivo from the peptide GH secretagogue GHRP-6. MK-677 also activates ghrelin receptors. MK-677 is active after oral administration in animals and humans. It is reported to increase the secretion of GH, insulin-like growth factor 1 (IGF-1), and IGFBP-3 levels in children with GH deficiency. It also produces sustained increases in the plasma levels of these hormones without affecting glucose, prolactin, triiodothyronine (T3), thyroxine (T4), and insulin levels. Most studies report no effects on cortisol, but there are human and laboratory animal studies that report MK-677 can increase cortisol (use w/ caution).