Medical education reviewed by Domenico Savatta, MD, FACS on July 23, 2026; educational use only. Care routing remains closed.
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Circadian rhythm disorder guide

Non-24-hour sleep-wake disorder: sleep timing drifts because the internal day does not stay aligned

In non-24, the sleep period progressively shifts later or sometimes earlier across days because the circadian system is not stably synchronized to the 24-hour day. It is especially associated with total blindness but can occur in sighted people.

Medically reviewed July 23, 2026 • Clinical reviewer: Domenico Savatta, MD, FACS • Educational use only

Document the timing driftMedication questions

Direct answer

What is non-24-hour sleep-wake disorder?

Non-24 is a circadian disorder marked by a recurring drift in sleep and wake timing, producing alternating periods of better alignment and severe insomnia or daytime sleepiness. Diagnosis requires a longitudinal pattern, not a single irregular week.

  • Irregular habits, shift work and delayed phase can resemble non-24.
  • Blindness, light perception, eye disease and light-sensitivity medicines change treatment.
  • Melatonin or receptor agonist timing is a medical decision, not a generic bedtime supplement.

At a glance

  • Track at least several weeks when the clinician requests it.
  • Record sleep timing, function, light perception and external schedule.
  • Use actigraphy and circadian markers when needed.
  • Review eye, neurologic, psychiatric and medicine context.
  • Treatment aims to entrain the clock, not only sedate at bedtime.

Drift is the defining pattern

The sleep window moves across clock time.

The person may cycle between nights of easier sleep and periods of severe mismatch. A static late bedtime is more consistent with delayed phase.

Blindness changes circadian input

Lack of light perception removes the strongest time cue.

Document vision and light perception accurately; do not assume every blind person has non-24.

Long records are often required

A short diary may capture only one phase of the cycle.

Use the requested diary, actigraphy and possibly circadian-marker testing to demonstrate repeated drift.

External routine still matters

Meals, activity, social schedule and light are secondary time cues.

Record them by clock time so the clinician can distinguish behavior from endogenous drift.

Treatment timing is precise

Light, melatonin and melatonin-receptor medicines can help selected patients.

Dose and clock time depend on phase, vision, conditions and medicines. Incorrect timing can fail or move the clock the wrong way.

Safety and accommodations matter

Misalignment can create severe sleepiness during required activity.

Plan transportation, work or school flexibility and follow-up while entrainment is being assessed.

Appointment checklist

Capture a full drift cycle

The clinician may need more than two weeks to see the moving phase.

  1. 1

    Sleep timing

    Record bed, sleep onset, wake, out-of-bed time and naps daily.

  2. 2

    Phase effects

    Record nights of easier sleep and periods of insomnia or daytime sleepiness.

  3. 3

    Vision and cues

    Document light perception, eye disease, light exposure, meals, activity and social timing.

  4. 4

    Treatment clock

    Record exact light or medicine time, adherence, response and side effects.

Common questions

Questions patients ask first

Is non-24 only found in blind people?

It is most associated with total blindness but can occur in sighted people; diagnosis still requires documented drift.

How is it different from delayed sleep phase?

Delayed phase is stably late; non-24 progressively moves across clock time.

Can a smartwatch diagnose it?

No. Actigraphy can support evaluation, but diagnosis requires clinical interpretation and sufficient longitudinal data.

Does melatonin cure non-24?

Timed therapy may entrain selected patients, but response and continued need require monitoring.

Authoritative sources

Review the public guidance

Medically reviewed by Domenico Savatta, MD, FACS on July 23, 2026. Source links support education, not a personal recommendation.