Why does the timing of melatonin matter more than the size of the dose for jet lag?

Answer: Melatonin acts as a darkness signal that tells the body clock when night is arriving.

A larger dose can choose whether the body clock shifts earlier or later. — A larger dose does not tell the clock whether to move earlier or later; that choice comes from when you take it. The misconception gets this much right: dose is part of what you can change. But jet-lag guidance separates eastward and westward timing, not bigger versus smaller pills. A high dose at the wrong hour does not fix that direction problem.

Melatonin acts as a darkness signal that tells the body clock when night is arriving. ✓ — Melatonin is read by the body as a darkness signal, so it can shift the clock toward night at the destination. The timing of that signal controls whether the clock moves earlier or later, not the dose. Travel advice treats eastward and westward trips differently for this reason. A small dose taken at the right time can do more than a large dose taken at the wrong time.

Melatonin repays lost sleep, so a larger dose lets the body clock catch up. — Melatonin is not a way to repay lost sleep; it helps signal when the body should treat the time as night. The misconception gets this much right: melatonin can make sleep at an unusual hour easier. But jet lag comes from a clock that is still set to home time, not from a sleep debt balance. The useful variable is timing, not the largest possible dose.