Leptin is a protein hormone with important effects in regulating body weight, metabolism and reproductive function. Leptin is a 16-kD protein that plays a critical role in the regulation of body weight by inhibiting food intake and stimulating energy expenditure. Defects in leptin production cause severe hereditary obesity in rodents and humans.

In addition to its effects on body weight, leptin has a variety of other functions, including the regulation of hematopoiesis, angiogenesis, wound healing, and the immune and inflammatory response. Leptin acts through the leptin receptor (LEPR), a single-transmembrane-domain receptor of the cytokine receptor family, which is found in many tissues in several alternatively spliced forms. The LEP gene is the human homolog of the gene (ob) mutant in the mouse 'obese' phenotype.