What is Non-24 Hour Sleep Wake Disorder?


Non-24 hour sleep wake disorder is a type of circadian rhythm disorder. People with the disorder are unable to align their bodies with the standard human 24-hour sleep wake cycle (1). They tend to have regular sleep-wake patterns, but these patterns are longer than 24 hours. As a result, people with non-24 hour sleep wake disorder go to sleep and wake up an hour or two later each day (2).

Causes of Non-24 Hour Sleep Wake Disorder

Non-24 hour sleep wake disorder occurs less frequently than other circadian rhythm disorders. The syndrome occurs primarily in people who are blind (3). Between 40% and 60% of people who are blind (4) experience non-24 hour sleep wake disorder.

Some individuals who are completely blind are unable to receive light input to the brain (5). Without light input, the person experiences a free-running circadian rhythm misaligned with the standard 24-hour day. While most individuals have an instinctive circadian rhythm of about 24.2 hours, light cues help the body regulate to 24 hours.

In some cases, people with full sight can also experience non-24 hour sleep wake disorder. The cause of non-24 hour sleep wake disorder in sighted individuals is not fully known. Experts hypothesize that some individuals have even longer intrinsic circadian rhythms and therefore struggle to adapt to the standard 24-hour cycle.

Symptoms of Non-24 Hour Sleep Wake Disorder

The main symptom of non-24 hour sleep wake syndrome is a person’s inability to synchronize their sleep time to match socially standard sleep times. The individual sleeps during uncommon periods of the day or night. They struggle to match up their sleep patterns with the common sleep schedules, and instead cycle between going to bed earlier and later than they'd prefer. Occasionally their sleep rhythm aligns with a standard 24-hour day, but it can take between three and 26 weeks for that to happen.

Diagnosis can be difficult because other sleep disorders may be affecting the irregular sleep pattern. If you think you have non-24 hour sleep wake disorder, your physician may ask you to keep a record of your sleep in a sleep diary. Additionally, diagnosis comes from observation of melatonin and cortisol rhythms. Observation takes several weeks of recording the levels of these hormones in urine, saliva, or blood.

Risks of Non-24 Hour Sleep Wake Disorder

For individuals who have non-24 hour sleep wake disorder, staying awake during regular daytime hours can be a challenge. They often experience symptoms of insomnia, such as a lack of energy, increased anxiety or depression, and difficulty learning or remembering (6).

When people with non-24 hour sleep wake disorder are forced to adhere to the standard 24-hour schedule, they are at great risk for excessive daytime sleepiness. Unfortunately, excessive daytime sleepiness can lead to mistakes, accidents, and injuries. Sleepy workers are 70% more likely (7) to be involved in an accident in the workplace. Drivers with less than six hours of sleep are 33% more likely (8) to be involved in a crash.

Non-24 Hour Sleep Wake Disorder vs. Other Circadian Rhythm Disorders

Circadian rhythm disorders are disorders in which a person’s internal clock is misaligned with the standard social clock. These disorders may occur due to day-to-day activities such as shift work or flying across time zones. They may also be caused by head trauma, or Alzheimer’s or Parkinson’s disease.

Non-24 hour sleep wake disorder falls in the category of altered sleep phase circadian rhythm disorders. The most common of these is delayed sleep phase disorder. Individuals with this disorder experience sleep onset two to six hours later (9) than most conventional sleep times. An estimated 1.1% of the general population experiences delayed sleep phase disorder.

Another common altered sleep phase circadian rhythm disorder is advanced sleep phase disorder. Common among older adults, this disorder occurs when people fall asleep and wake up early and are unable to change their sleep pattern.

Non-24 hour sleep wake disorder differs from other circadian disorders because it predominantly affects people who are blind. Treatments for the disorders also differ.

Treatment for Non-24 Hour Sleep Wake Disorder

Treatments for non-24 hour sleep wake syndrome may depend on if the patient is blind or sighted. Additionally, these treatments vary from treatments for other circadian rhythm disorders. For example, while caffeine can help people with non-24 hour syndrome stay awake (10), it cannot appropriately address sleep schedule and sleepiness. Therefore, experts do not recommend caffeine as a treatment for this disorder.


Melatonin is a hormone that helps promote sleep. Many circadian rhythm disorders, including non-24 hour sleep wake disorder, are treated with melatonin. Patients take melatonin supplements in the early evening hours so that they can fall asleep at a normal bedtime. Unfortunately, discontinuation of melatonin leads to a high risk for relapse (11).


Similar to melatonin, tasimelteon promotes sleep. This medication must be taken at the same time each night (12). Some users report weeks or even months of usage before the medicine takes effect in improving the sleep cycle. Additionally, the medication is expensive and can only be purchased from specialty pharmacies by mail.

Light Therapy

Exposure to bright light therapy is commonly used to treat other circadian rhythm disorders. In contrast, research shows that light therapy alone cannot improve non-24 hour sleep wake disorder. Instead, bright light therapy should be used in the morning in combination with taking melatonin at night. However, this therapy is not appropriate for people who are blind and do not receive light input because the disorder is caused by the inability to recognize light.

Life with Non-24 Hour Sleep Wake Disorder

While living with non-24 hour sleep wake disorder can be challenging, treatment is available. If you suspect you have the syndrome, consult with your physician to make a plan for diagnosis and treatment. With time, you can develop strategies for regulating your sleep cycle and keeping a consistent sleep and wake schedule.

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