Orexin, also known as hypocretin, is an excitatory neuropeptide secreted by the hypothalamus. Orexin is divided into orexin-A (OXA) and orexin-B (OXB), which are derived from a common precursor secreted by hypothalamic neurons. Orexin acts on orexin receptor-1 (OX1R) and orexin receptor-2 (OX2R). Orexin neurons, as well as receptors, are widely distributed in various regions of the brain as well as in the peripheral system and have a wider range of functions. This paper reviews the latest research results of orexin in the aspects of food intake, sleep, addiction, depression and anxiety. Because orexin has certain physiological functions in many systems, we further explored the possibility of orexin as a new target for the treatment of bulimia, anorexia nervosa, insomnia, lethargy, anxiety and depression. It is precisely because orexin has physiological functions in multiple systems that orexin, as a new target for the treatment of the above diseases, has potential contradictions. For example, it promotes the function of 1 system and may inhibit the function of another system. How to study a new drug, which can not only treat the diseases of this system, but also do not affect other system functions, is what we need to focus on.