MC3R (melanocortin 3 receptor) is a G protein-coupled receptor that serves as a central regulator of energy homeostasis and developmental timing. The receptor binds melanocyte-stimulating hormones and ACTH, activating cAMP-dependent signaling pathways to control multiple physiological processes 1. MC3R plays distinct roles from the related MC4R, with MC3R primarily regulating calorie disposition into growth, lean mass, and sexual maturation timing rather than calorie acquisition 2. Loss-of-function mutations in MC3R are associated with delayed puberty, reduced linear growth, decreased lean mass, and lower IGF1 levels in humans 2. The receptor also functions in peripheral tissues, particularly the liver, where it regulates lipid droplet autophagy and hepatic steatosis through activation of autophagy pathways 3. Common MC3R polymorphisms (Thr6Lys and Val81Ile) show associations with childhood obesity, with homozygous carriers of the Thr6Lys variant having a 3.10-fold increased risk of overweight/obesity 4. Beyond metabolic functions, MC3R contributes to circadian rhythm regulation and has emerging roles in ocular homeostasis and immune privilege 5. The receptor represents a promising therapeutic target for metabolic disorders, with specific agonists showing potential for treating obesity and fatty liver disease 6.