The circadian rhythm is typically a 24 hour internal clock that runs automatically. It tells your brain when to cycle between sleepiness and alertness. This is also known as a sleep-wake cycle. Part of the brain’s hypothalamus controls the circadian rhythm which works with the pituitary and eyes, among other things. In typical people, the circadian rhythm is highly influenced by light signals. For example, a sunset (dimming lights) triggers the body to make melatonin, which typically prepares people for sleep. The circadian rhythm is incredibly complex, not fully understood, and multi-systemic.

Non-24 simply means a person’s circadian rhythm is not on a 24-hour day. Most Non-24 patients are blind, but sighted people can have it, too.

In totally blind people, the lack of light perception throws the circadian rhythm out of sync; their circadian rhythms are typically normal otherwise. This may make it easier for blind patients to entrain to a normal 24 hour day using medication.

In sighted people, there is no singular cause and many factors can be at play. Sighted Non-24 is typically more complex and may not respond to the same therapies as cases of Non-24 caused by blindness.

The primary sign is a sleep–wake cycle longer than 24 hours, usually averaging 25-26 hours. In someone who is forcing their sleep with alarms, this may look like cyclical insomnia or insomnia that comes in waves. When your circadian rhythm is not aligned with your schedule, you would have insomnia and symptoms of sleep deprivation, but when it is aligned, you would sleep fine.

In Sighted Non-24 patients, the retina may not react naturally to light. People with Sighted Non-24 can be subjectively sensitive to light (photophobia), or they can be under-sensitive to bright light.

Those of us with Sighted Non-24 typically sleep well and have an average habitual sleep duration of nine to ten hours, but we cannot sleep at the same time every day. This leads to a forward shift.

Sighted Non-24 is not well studied by researchers yet, but we know of several causes.

  • It may be a neurological disorder with an abnormal functioning of the suprachiasmatic nucleus (SCN) in the hypothalamus.
  • It could be due to the retina being too sensitive or not sensitive enough to light signals.
  • Sometimes, Delayed Sleep Phase Syndrome can develop into Non-24. This is often due to chronotherapy. Chronotherapy is a “treatment” prescribed by patients with DSPS to try and slowly adjust their sleeping habits. Doctors ask patients to force their sleep to a cycle their circadian rhythm is not used to and this can create an elongated circadian rhythm (Non-24).
  • A pituitary adenoma can cause Non-24. This is a small benign tumor that disrupts the typical flow of chemicals that control hormones, particularly those related to sleep like melatonin.
  • There may also be genetic factors at play. Researchers are currently studying the genetic involvement that may be present in Sighted Non-24. Dr. Alina Patke and her associates at The Rockefeller University are among those studying how genetics are involved in circadian rhythms.
  • Some Sighted Non-24 patients are neurodivergent or are on the autism spectrum. For some, the differences in neurology may play a role.
  • There are likely other unknown causes. We hope raising awareness will inspire researchers to continue searching.

Usually, patients are diagnosed by filling out a sleep log and showing it to a sleep specialist or a neurologist with a sleep specialty who is literate in Non-24. Non-24 Sleep–wake disorder is diagnosed when the patient fails to follow (entrain to) a 24-hour light-dark cycle and typical wake times. 

This graph is an example of a Non-24 sleep pattern with a semi-predictable forward shift. The date is horizontal and the sleep time is vertical. It shows a semi-predictable pattern and then shows the patient forcing themselves to stay awake on 2/25; then, the pattern tries to correct itself to the patient’s abnormal (Non-24) circadian rhythm.

For information on keeping sleep logs, visit our Resources page.

Treatment for Sighted Non-24 will depend on the underlying cause. For many patients, they find improved health if they sleep whenever they are sleepy and wake when they feel refreshed. This is called free-running. While free-running is not the most convenient option, it decreases the risk of sleep deprivation and its adverse long-term effects.

Sometimes, strict light and/or dark therapy can help those with Sighted Non-24 hold on to a 24-hour day.

Low dose melatonin under doctor supervision has also been known to help some and can be used in conjunction with light and/or dark therapy to increase effectiveness.

The pharmaceutical company Vanda developed a drug called Hetlioz (tasimelteon) specifically to treat Non-24. It has been known to be effective for some Sighted Non-24 patients, but usually requires patients appeal to their insurance company because it is expensive at around $60,000 per year without insurance coverage. It comes from a specialist pharmacy. It is also relatively unknown, as fewer than 1,000 people are currently using Hetlioz.

However, some patients may not find improvement with any of these known treatments and may find that free-running is their best option.

More info at Circadian Rhythm Disorders Network for Sighted Non-24 Treatment Options

Free-running sleep is a sleep pattern that is not adjusted (entrained) to the 24-hour cycle in nature nor to any artificial cycle.

Free-running sleep means that a person with Non-24 chooses to sleep when sleepy and to awaken spontaneously (specifically without an alarm clock or reference to the time of day). Put simply, free-running means following the body’s natural rhythm.

For many with Sighted Non-24, sleeping on a normal schedule may be difficult or impossible and trying to do so results in sleep deprivation and elevated stress levels… with all the harmful health effects that accompany sleep deprivation.

Sighted Non-24 patients often find they can be much more productive and happier living on the rotating schedule to which their body naturally adheres to. For people with severe cases of Non-24, free-running may be the only realistic option.