Melatonin's effect peaked near 4 mg taken three hours before bed
Across 26 trials the sleep effect peaked near 4 mg a day rather than climbing with dose, and moving it to about 3 hours before bed improved falling asleep and sleep length.
What the study found
The modelled optimum is 4mg of melatonin, 3 hours before bed
More is not better, and 30 minutes before bed is not early enough. Across 26 trials, melatonin's sleep-promoting effect peaked near 4mg a day rather than climbing with the dose, and moving it to about 3 hours before bed improved both how fast people fell asleep and how long they slept.
The caveat · No trial ran this exact regimen
That pairing is the peak of a curve drawn across many different trials, not a regimen any single trial actually ran. Nobody has yet put it head to head against the usual 30-minutes-before dose, which is the comparison that would settle it. The pooled trials span 1987 to 2020 and differ widely in whom they enrolled.