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What is Non-24 Hour Sleep Wake Disorder?

For many, the 24 hour day is essential in delineating sleep and wake times. Not only do humans rely on the normal progression of a day but also plants and animals. Our circadian clock, an internally generated 24-hour rhythm regulates the 24 hour cycle of biological processes including sleep and hormone production. However, there are many individuals who do not operate by this 24 hour cycle.


Non-24 Hour Sleep Wake Disorder (N24HSWD) is characterized by a lack of synchronization of the circadian rhythm. The suprachiasmatic nuclei (SCN), residing inside the hypothalamus of the brain, detects the day-night cycle as the primary environmental cue that synchronizes the circadian clock to the 24-hour day. Individuals with N24HSWD, however, have circadian clocks that fail to synchronize with the 24 hour day, either by failure of light to reach the SCN or other abnormal neurological functioning.


Occurring mostly in people who are blind, N24HSWD creates delayed sleep and wake periods. When light is not recognized by the retina the SCN is not activated to begin the 24-hour day so many of us are accustomed to. There is still a lot of research to be done on those who are not blind and suffer from N24HSWD, but it is believed that head injuries resulting in trauma to the internal neurological processes are one of several possible culprits.


Those affected by the non-24-hour cycle experience daily shifts in their wake and sleep times and often go weeks or months getting bad sleep before their circadian cycle is complete. This makes it extremely difficult for these individuals to interact within the same social 24-hour day that most of us take for granted.


There are few treatment options for those with N24HSWD. For sighted individuals there is re-synchronizing of the internal circadian clock by administering light at the appropriate times. For those who cannot see, melatonin can be administered. Melatonin signals darkness to the brain and can shift the circadian clock forwards or backwards depending on the time of day it is administered. While both methods show promise, there is currently no permanent cure for N24HSWD.


Do you know anyone with Non-24 Sleep Wake Disorder? Let us know what you think about this disorder in the comments section below.

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3 Responses so far.

  1. Kasha says:

    I don’t know many Non-24’s that find melatonin or light therapy promising. It’s a bit more complicated than that. The majority of Sighted Non-24’s did not get theirs from a head injury and they do best on their natural rhythm. Even using melatonin and light, forcing yourself to be on a 24 hour schedule is not natural and makes us sick. Much like forcing everyone else to be on a 26 hour schedule would make them sick.

    • Kelsey Kusterer says:

      Kasha, you’re right, non-24 hour sleep-wake disorder is very difficult to treat. Recently the FDA approved the first treatment for this disorder, called Hetlioz. This drug has shown promising results since it significantly improved symptoms for clinical trial patients. We published a follow-up blog to this one which describes the new treatment

      • Christine says:

        I am a sighted individual with non-24. My sleep clinic doctor told me about tasimelteon and it sounds really hopeful, but I’ve been unable to find any information about how to get it here (Canada), and the information about the US I’ve found lists it at $250 per pill. Utterly frustrating.