In one study, 746 adults with PI, aged 18 to 80, took melatonin or a placebo two hours before bedtime. While the placebo group did not improve at any time, after three weeks, those 55 or older who took melatonin fell asleep more quickly, and over the next six months, the melatonin group slept better.
After treatment, there were no withdrawal or tolerance symptoms, and no rebound insomnia. Researchers said melatonin is effective for PI in the short- and long-term.