Delayed sleep phase is a sleep disorder that affects the internal clock, known as circadian rhythm. People with this sleep disorder have sleep patterns that are delayed two hours or more from usual sleep patterns. They go to sleep later and wake later. This makes it hard to wake in time for work or school. Delayed sleep phase also is known as delayed sleep-wake phase disorder.

A treatment plan might include making changes to sleep habits, taking melatonin supplements and using light therapy.


People with delayed sleep phase fall asleep and wake later than they want and later than usual sleep and wake times. Sleep and wake times are delayed at least two hours and may be delayed up to 3 to 6 hours. People with delayed sleep phase may regularly go to sleep at 3 a.m. and wake at 10 a.m., for example.

Symptoms are persistent. They last at least three months and often for years. Symptoms may include:

  • Not being able to fall asleep at a typical bedtime, known as insomnia.
  • Trouble waking up in the morning in time to go to work or school.
  • Extreme daytime drowsiness.
  • Trouble staying alert during the day.

When to see a doctor

See a health care professional if you have persistent symptoms of delayed sleep-wake phase disorder. Or make an appointment for your child if you think your child has symptoms of delayed sleep-wake phase disorder that don't go away.

Also make an appointment if you or your child regularly has trouble waking in the morning or has excessive daytime drowsiness.


Delayed sleep phase is caused by a person's internal clock being out of sync with the environment. Your internal clock lets you know when it's time to sleep and when it's time to wake. Known as circadian rhythm, your internal clock is on a 24-hour cycle. Cues in the environment influence the sleep-wake cycle. These cues include light, darkness, eating and physical activity.

The exact cause of delayed sleep phase isn't known. But circadian rhythms can be delayed in teenagers for biological reasons. Staying up late to do homework, watch TV or use the internet can make the sleep delay worse.

Risk factors

Delayed sleep phase can affect children and adults of any age. However, delayed sleep phase is more common among teenagers and young adults.

Sept. 21, 2023
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