Begun after landing, melatonin may help; begun days before, it did not
In 52 cabin crew, 5 mg begun after arrival eased jet lag; begun three days before arrival, it did no better than placebo.
What the study found
Cabin crew gained from melatonin begun after landing, not days before
In 52 cabin crew, 5 mg of melatonin started after arrival eased jet lag against placebo, while the same dose started three days before arrival did no better than placebo. A 2002 review of ten trials read them the same way: doses before the travel day add nothing.
The caveat · Crew clocks already scrambled
The crew's body clocks were already scrambled by back-to-back flights, so the early doses landed at varying body-clock times. Only the ratings recalled on day 6 separated the groups, while the daily ratings showed trends. A crew's working days are not an ordinary traveller's.
What we don't know
The only trial to compare start times found that beginning melatonin days before arrival did no better than placebo, while a pooling across trials leaned the other way. Whether a pre-flight start helps ordinary travellers is unsettled.