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★☆☆Contested — the evidence disagrees with itself, or the finding carries a caution. A caution or conflict always shows one star, however strong the sources are.
Caffeine may fight jet-lag drowsiness by day, melatonin help at night
In one trial of 27, nine per group, slow-release caffeine cut daytime sleepiness but tended to worsen sleep; melatonin helped sleep but not daytime sleepiness.
What the study found
Caffeine kept jet-lagged reservists alert; melatonin helped them sleep
In 27 air force reservists flown seven time zones east, nine per group, 300 mg of slow-release caffeine each morning cut measured daytime sleepiness but tended to worsen sleep. Melatonin, 5 mg, helped recovery sleep but not daytime sleepiness. Each answered a different half of jet lag.
The caveat · Directions only, no sizes reported
The trial reported which way each measure moved, not by how much. Nine people took each treatment, and three published papers all describe the same 27. The caffeine was a slow-release tablet, not coffee.