Orexin has a key function in human neurology and physiology. It is a regulator in and around the hypothalamus which affects one's hunger, fatigue and general arousal. Though i…ts quantity in our anatomy is far less than that of of other neurotransmitters, its role is no less important. (MORE)

Orexin replacement therapy research is still in its early phases. Scientists are testing it on dogs with narcolepsy.