Non-24-Hour Sleep-Wake Rhythm Disorder (Non-24) is a circadian rhythm disorder

Last updated: June 2026 - Reviewed by the Apexzen editorial team

Part of: Sleep Disorders Atlas > Circadian Rhythm Disorders

What is it? Non-24-Hour Sleep-Wake Rhythm Disorder (Non-24) is a circadian rhythm disorder where an individual's internal body clock is not synchronised to the 24-hour light-dark cycle of the environment. Instead, their internal clock "free-runs" on its own natural cycle, which is typically slightly longer than 24 hours. This causes their sleep and wake times to drift later and later each day, eventually cycling completely around the clock over a period of weeks. This condition is most common in people who are blind and cannot perceive light cues to reset their internal clock daily.

The symptoms of a free-running clock

• A sleep schedule that predictably shifts later every single day
• A recurring, cyclical pattern of sleep problems
• Periods of severe nighttime insomnia, when the internal clock promotes wakefulness during the night
• Periods of severe daytime sleepiness, when the internal clock promotes sleep during the day
• A temporary period where the schedule feels "in sync" before the drift continues
• An inability to hold a conventional sleep-wake schedule for more than a day or two

What actually helps

The goal of treatment is to "entrain", or lock, the free-running body clock into a stable 24-hour rhythm. For blind individuals, this is often achieved with medication, such as a specifically timed melatonin receptor agonist prescribed by a doctor.

For sighted individuals with Non-24, treatment involves a very strict and structured daily regimen of chronotherapy: precisely timed bright-light therapy on waking, structured periods of darkness (light avoidance) in the evening, and sometimes a strict activity schedule. The common thread is precision and consistency, which is why this is supervised by a clinician rather than self-managed.

When to see a specialist

Because of its complexity and the difficulty of treatment, Non-24 almost always requires a diagnosis and management plan from a sleep specialist or a chronobiologist. If you or someone you know has a constantly rotating sleep pattern that cannot be stabilized, seeking professional help is the essential first step to getting an accurate diagnosis and a tailored treatment plan.

Frequently asked questions

Why is Non-24 so common in blind people?

Light is the main signal that resets the body clock each day. People who are totally blind cannot perceive that signal, so the clock has nothing to lock onto and free-runs on its own cycle, which is usually slightly longer than 24 hours. That is why the schedule drifts.

Can I treat Non-24 on my own?

No. Non-24 is complex and the treatment relies on precise timing and often prescription medication. It almost always needs a sleep specialist or chronobiologist to diagnose and supervise. Self-managing it rarely stabilises the clock.

Is Non-24 the same as delayed sleep phase syndrome?

No. In delayed sleep phase syndrome the clock is shifted late but stays on a stable 24-hour pattern. In Non-24 the clock is not locked to 24 hours at all, so sleep keeps drifting later each day rather than settling at a fixed late time.

Related reading: Delayed Sleep Phase Syndrome, Advanced Sleep Phase Syndrome, and Chronic Insomnia.

Sources: American Academy of Sleep Medicine, International Classification of Sleep Disorders (ICSD-3) and clinical guidance on Non-24-Hour Sleep-Wake Rhythm Disorder.

This article is for educational purposes only and is not medical advice. These statements have not been evaluated by the Food and Drug Administration. Apexzen products are not intended to diagnose, treat, cure, or prevent any disease. Consult a qualified healthcare provider for persistent sleep problems.