What is delayed sleep phase, and does my teenager have it?

The short answer

Delayed sleep-wake phase disorder is more than choosing a late bedtime. The main sleep period is consistently shifted later than the times school, work or family life require. A teenager may be unable to fall asleep until very late, extremely difficult to wake for obligations and much more able to sleep normally when allowed their preferred later schedule. One weekend, holiday or phone-heavy night does not establish it. Keep a sleep-and-wake record across school days and free days for at least two weeks, noting estimated sleep onset, waking, naps, light exposure, caffeine, medication, mood, breathing and daytime functioning. Speak to the GP when the pattern is persistent and causes missed education, severe difficulty waking, distress or daytime impairment. Do not start melatonin, use high-intensity light treatment or repeatedly force an abrupt schedule change without clinical advice; timing matters, and other sleep, physical or mental-health problems may look similar or coexist.

• Delayed sleep-wake phase is a persistent timing pattern, not a judgement about motivation.
• Compare school days with days when the teenager can choose their own sleep window.
• Record sleep timing and daytime impact for at least two weeks.
• Rule out insufficient sleep, anxiety, medication effects, breathing problems and other causes.
• Melatonin and timed light are not do-it-yourself timing experiments.