In most people, administration of the hormone leptin does not lead to any weight loss or fat burning, according to WebMD. Administration of leptin only leads to weight loss in extremely rare cases of individuals who do not manufacture any of their own leptin.
Leptin is normally manufactured by fat cells. Under normal circumstances, if the body has sufficient fat in storage, leptin levels rise and signal the brain that food is not necessary, says WebMD. However, in many overweight individuals, a state called leptin resistance develops in which the brain does not respond to high levels of leptin by down-regulating appetite. Administering extra leptin to overweight individuals who have developed leptin resistance has no effect on appetite.