Overview of Brain Chemical Orexin

Brain Chemical Affects Wakefulness with a Role in Narcolepsy and Insomnia

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What is orexin? Also known as hypocretin, learn how this chemical in the brain impacts wakefulness and has an important role in both narcolepsy and a new treatment for insomnia called Belsomra.

Defining Orexin

Orexin is a chemical messenger (or neurotransmitter) that is produced in an area of the brain called the hypothalamus. It affects the brainstem and stimulates food intake, wakefulness, and energy use (metabolism).

It is part of a class of substances called excitatory neuropeptide hormones. This means that it works to excite activity of other cells, in effect "waking up" their activity.

There are two different peptides with a similar chemical structure: one is orexin-A (or hypocretin-1) and the other is orexin-B (or hypocretin-2).

Orexin's Role in Narcolepsy and Insomnia

Orexin has a central role in promoting wakefulness. When it is lost, as occurs in narcolepsy, episodes characterized by the sudden onset of sleep may occur. 

There is also some evidence that blocking the signal for orexin may help to induce sleep. As a result, a new class of sleep medication called an orexin antagonist has become available. It is called Belsomra and is sold under the generic name suvorexant.


Kryger, MH et al. "Principles and Practice of Sleep Medicine." Elsevier, 5th edition, 2011.

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