Leptin is a naturally occurring hormone and an important regulator of energy homeostasis and other diverse physiological functions. Circulating levels of leptin closely correlate with the amount of adipose tissue present. Metreleptin, a recombinant analogue of human leptin, is a 147-amino acid polypeptide that differs from the human leptin sequence by 1 additional amino acid, methionine, located at the amino-terminal end. Metreleptin has the same physiological effects as leptin, including regulation of energy homeostasis and metabolic function.