Medical Definition of orexin
: either of two neuropeptides (orexin A and orexin B) that are produced in the hypothalamus and play a role in regulating wakefulness and food intake Scientists have known for almost a decade that narcolepsy is caused by a dearth of a brain communication chemical called orexin.—Laura Sanders, Science News, 24 Oct. 2009 The new sleep aids block the activity of brain peptides called orexins.—Christine Soares, Scientific American, July 2010—called also hypocretin
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