Melatonin may help some individuals fall asleep by dropping core body temperature, not by generating sleep.

“One of the reasons that I've become a little bit more bullish on melatonin from a sleep perspective and then melatonin more generally for a, maybe you can speak about this too, as a counter measure when you're undergoing insufficient sleep. There are two different routes there. The first reason that I think it could have a sleep benefit for some people is not because it helps in the generation of sleep, we know that it doesn't, it's because it too seems to drop core body temperature.”