1) Leptin is a hormone produced mainly by adipose tissue that plays a key role in regulating appetite and energy expenditure. 2) It acts in the hypothalamus by binding to leptin receptors and stimulating anorexigenic peptides while inhibiting hunger signals like neuropeptide Y. 3) Mutations that cause leptin deficiency or leptin receptor deficiency result in obesity that can be treated with replacement of leptin or combined leptin and amylin therapy, demonstrating the important role of leptin in regulating body weight.