For some people, melatonin seems to help improve sleep. However, when scientists conduct tests to compare melatonin as a "sleeping pill" to a placebo (sugar pill) most studies show no benefit of melatonin. Evidence that melatonin can reset the body clock is more well established, although it is not clear whether exposure to light may be more effective. Overall, research indicates improved sleep when melatonin is taken at the appropriate time for jet lag and shift work. Appropriate dosage and any safety risks will become clear with further research.
Some studies show promise for the use of melatonin in shortening the time it takes to fall asleep and reducing the number of awakenings, but not necessarily total sleep time. Other studies show no benefit at all with melatonin.
Large studies are needed to demonstrate if melatonin is effective and safe for some forms of insomnia, particularly for long-term use. It may be true that melatonin is effective and safe for some types of insomnia and for children but not for other types of sleep problems. How much to take, when to take it and its effectiveness, if any, for particular disorders is only beginning to be understood.