orexin

noun

orex·​in ə-ˈrek-sən 

: 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

The new sleep aids block the activity of brain peptides called orexins.

—Christine Soares, Scientific American

called also hypocretin