People with delayed sleep-phase syndrome (DSPS) have trouble falling asleep before 2 a.m., sleep restlessly, have great difficulty waking in the morning, and often sleep less than seven hours. About half of those with DSPS also have depression.
In one study, 20 people with DSPS, eight of whom also had depressive symptoms, took 5 mg of melatonin per day or a placebo. After four weeks, compared to placebo, depressed participants who had taken melatonin had far fewer depressive symptoms. Also compared to placebo, all depressed and non-depressed participants in the melatonin group enjoyed more continuous sleep throughout the night.