MK-677 acts as a ghrelin receptor (GHS-R1a) agonist. By binding to the ghrelin receptor in the brain (particularly in the pituitary and hypothalamus), it triggers the secretion of growth hormone in a pulsatile fashion – effectively simulating the effect of ghrelin without actually making you hungry (though it does still tend to increase appetite). This leads to elevated GH and subsequently IGF-1 levels in the bloodstream, creating an anabolic environment. The increase in IGF-1 is one of the primary reasons for muscle growth, improved recovery, and potential fat loss; IGF-1 supports muscle cell differentiation and growth. MK-677’s GH-boosting effect also causes enhanced lipolysis (fat breakdown), improved nitrogen retention, and collagen synthesis (good for joints, skin, and connective tissue). Importantly, it does all this without stimulating cortisol or other stress hormones (unlike some peptides). Additionally, ghrelin has roles in the brain related to hunger and mood – by agonizing its receptor, MK-677 tends to increase appetite significantly, and some users report improved mood or cognitive effects. Another noted effect is on sleep: growth hormone is tied to deep sleep cycles, and MK-677 often deepens sleep and can increase REM duration, which is beneficial for recovery and memory consolidation. Overall, MK-677 essentially signals the body to act as if it’s in a state conducive to growth (plentiful food, high ghrelin), thereby raising anabolic hormone levels and promoting tissue building and repair.