Phase-delayed circadian rhythm can be helped by which therapy?

• A. Afternoon naps
• B. Morning light exposure
• C. Caffeine after noon
• D. Evening light exposure or melatonin in the early evening

Answer: (D)

For a phase-delayed circadian rhythm, the aim is to advance the clock so you sleep and wake earlier. Melatonin taken in the early evening acts as a signal that night is approaching, helping to shift the sleep–wake cycle earlier. The timing matters: a small dose a few hours before your desired bedtime can produce this phase advance.

In contrast, evening light exposure tends to delay the clock, which would make a phase delay worse. Caffeine after noon and naps in the afternoon don’t reliably realign the clock toward an earlier schedule. So the beneficial element here is taking melatonin in the early evening to advance the circadian phase.