Circadian rhythm disorders
Non-24-Hour Sleep-Wake Disorder
The body clock is not synchronised to the 24-hour day, so sleep times drift later each day. It mainly affects people who are totally blind.
Overview
Non-24-hour sleep-wake disorder (often called non-24) occurs when your body clock is not reset by light each day and runs on its own cycle, usually slightly longer than 24 hours. As a result, the time you feel sleepy drifts later day by day, cycling through periods of good sleep and periods of severe insomnia and daytime sleepiness.
It mostly affects people who are totally blind, because light reaching the eyes is the main signal that keeps the body clock aligned. It can also occur, less commonly, in sighted people.
Treatment aims to entrain, or lock, the body clock to the 24-hour day using timed melatonin or the prescription medicine tasimelteon.
Non-24 is estimated to affect more than half of people who are totally blind, while it is uncommon in sighted people.
Common symptoms
- Sleep times that drift later each day
- Weeks of good sleep alternating with weeks of insomnia
- Severe daytime sleepiness during misaligned periods
- Difficulty keeping regular schedules
- Napping at unpredictable times of day
Causes and risk factors
- Total blindness with no light perception
- Rarely, in sighted people: very little light exposure, delayed sleep phase history or brain injury
- Possibly a naturally longer body clock period
- Irregular daily routines that provide few time cues
How it is diagnosed
Diagnosis typically requires at least 14 days of sleep diaries and, where possible, actigraphy, showing sleep times drifting progressively later. In blind people, measurements of melatonin timing over weeks may be used to confirm the drifting rhythm.
Treatment options
Tasimelteon (Hetlioz)
A melatonin receptor medicine approved by the FDA for non-24, shown in trials to help entrain the body clock in totally blind people.
Timed melatonin
Taken at a consistent time each evening, often recommended by AASM guidance for blind adults with non-24.
Structured schedules
Regular meals, activity and social cues may support entrainment.
Light exposure (for sighted people)
Morning light can help when the eyes perceive light.
What you can do yourself
- Keep consistent daily routines
- Track sleep with a diary to spot the pattern
- Take any prescribed treatment at the same time every day
- Plan important activities when you feel most alert
When to see a doctor
- You are blind and experience cycles of insomnia and daytime sleepiness
- Your sleep time shifts later each day despite trying to keep a schedule
- Sleep problems disrupt work or family life
Frequently asked questions
Why does non-24 mostly affect blind people?
Light detected by the eyes is the main daily signal that resets the body clock. Without light perception, the clock can run on its own cycle and drift out of step with the 24-hour day.
Can sighted people have non-24?
Yes, though it is uncommon. In sighted people it may be linked to minimal light exposure, delayed sleep phase or neurological conditions.
What is tasimelteon?
Tasimelteon is a prescription melatonin receptor medicine approved by the FDA for non-24. Clinical trials in totally blind people showed it helped align the body clock.
Does over-the-counter melatonin work?
Melatonin taken at a consistent time each evening can help entrain the clock in some blind people. Ask a sleep specialist about timing and product quality.
Sources
This page is general information, not a diagnosis or medical advice. Read our medical disclaimer.