Melatonin supplementation increases total sleep time by an average of 3.9 minutes and sleep efficiency by 2.2% in healthy non-elderly adults.

“Sadly, the evidence in healthy adults who are not older age suggests that melatonin is not really particularly helpful as a sleep aid. I think there's a recent meta analysis that demonstrated when it looked at all of the different sleep parameters, melatonin, and a meta analysis for those not knowing what that is, it's a scientific sort of method that we use where we gather all the individual studies and we put them in a big bucket and we kind of do this kind of statistical fancy sleight of hand. And we try to come up with a big picture of what all of those individuals studies tell us. And what that meta analysis told us is that melatonin will only increase total amount of sleep by 3.9 minutes, on average.”