Jet lag happens because your internal body clock stays set to your departure time zone while the local clock has moved on; health authorities say it can start after crossing as few as two time zones. The strategies with the most evidence behind them are a pre-flight sleep shift, timed light exposure after landing, and, in some cases, correctly timed low-dose melatonin — not random napping or "pushing through."
What causes jet lag
According to the CDC's Yellow Book, the reference guide the agency publishes for travelers' health, jet lag disorder is a temporary mismatch between a person's internal circadian clock and the local time at a destination, and it can occur after crossing at least two time zones. The CDC lists common symptoms as insomnia, daytime sleepiness, impaired concentration, malaise and gastrointestinal disturbances.
Step-by-step plan for before, during and after the flight
About two to three days before departure, shift your bedtime and wake time by roughly one hour per day toward destination time, as recommended in the CDC Yellow Book.
Where flight choice allows, pick a departure or arrival time that puts you into favorable daylight at your destination; the CDC also suggests using a jet lag calculator for a personalized light and melatonin schedule.
Once on the plane, set your watch to destination time and base meals, sleep and light exposure on that clock rather than on your point of origin, per CDC guidance.
Stay hydrated in flight, keep alcohol intake low, avoid sedative medications with long half-lives, and go easy on caffeine if you want to sleep on board — all points the CDC raises for the in-flight period.
After landing, eat at local mealtimes and stay awake until local bedtime even if you feel exhausted; the CDC states this is more effective for resetting the clock than extended daytime napping.
Time your light exposure to the direction you traveled (see the table below); the CDC lists this as one of several tools — alongside timed melatonin, sleep scheduling and, in some cases, medication — for realigning the body clock.
If you choose to use melatonin, take it close to your target local bedtime rather than on a fixed schedule from home — see the dosing section below, and check with a clinician first.
Keep any naps short. The Sleep Foundation recommends capping naps at about 30 minutes and finishing them at least eight hours before your planned local bedtime so they do not delay nighttime sleep.
For trips of two days or fewer, CDC guidance suggests staying on your home time-zone sleep schedule rather than trying to fully adapt, since the body will not have time to resynchronize anyway.
Light exposure: eastward vs. westward travel
Light is the main signal the body uses to reset its clock, but the right timing depends on which way you flew. The CDC Yellow Book and a 2019 review in Frontiers in Physiology (accessed via PubMed Central) both describe opposite light strategies for eastward and westward trips.
Light-exposure strategy by travel direction
Direction
Seek light
Avoid light
Clock adjustment needed
Eastward (e.g., Europe→Asia)
Morning sunlight at destination
Evening light
Phase advance — move bedtime earlier
Westward (e.g., Europe→USA)
Evening/afternoon light at destination
Early-morning light
Phase delay — move bedtime later
The Frontiers in Physiology review adds a more specific point for eastbound travelers: it recommends avoiding sunlight before midday and maximizing exposure in the three to six hours after midday, so as not to send the body conflicting signals before the clock has shifted.
Melatonin: sources do not fully agree on dose
All three sources consulted for this piece endorse melatonin as a useful tool, but they differ on how much to take. The CDC Yellow Book says 0.5–1 mg is usually sufficient and advises against exceeding 5 mg. The Sleep Foundation cites low-dose supplements in the 1–3 mg range. The 2019 Frontiers in Physiology review, by contrast, reports that a 3.0 mg dose produced more reliable circadian phase shifts in study participants than a 0.5 mg dose. For timing, the CDC advises taking melatonin roughly 90 minutes before the target bedtime to help advance the clock on eastward trips, and near the destination's morning hour to help delay it on westward trips; it also notes that taking melatonin during the body's own natural melatonin-production window, roughly midnight to 5 a.m. local body time, is less effective at shifting the clock, and that taking it at the wrong time more generally can increase the mismatch rather than resolve it.
How long full adaptation takes
The Frontiers in Physiology review gives approximate adaptation timelines based on the size of the time-zone shift: for a 3-hour shift, partial adjustment appears by day 1 with full adaptation around day 4; for a 6-hour shift, partial adjustment by days 2–3 with full adaptation around day 6; for a 9-hour shift, partial adjustment by days 3–5 with full adaptation around days 7–8. The Sleep Foundation describes jet lag more broadly as lasting anywhere from a few days to a few weeks depending on the traveler and the size of the time change.
Caffeine, alcohol and other practical notes
The CDC Yellow Book advises avoiding caffeine close to bedtime, whether that sleep period is on the plane or after arrival, since caffeine can further disrupt an already unsettled sleep-wake cycle. It also advises keeping alcohol intake low in flight and avoiding long-acting sedatives, for the same reason.
Questions
How many time zones do you have to cross to get jet lag?
According to the CDC Yellow Book, jet lag disorder can occur after crossing at least two time zones, with symptoms generally worsening as more zones are crossed.
What is the right melatonin dose for jet lag?
Sources disagree slightly: the CDC Yellow Book cites 0.5–1 mg as usually enough (and advises against more than 5 mg), the Sleep Foundation cites a 1–3 mg range, and a 2019 Frontiers in Physiology review found 3.0 mg produced more reliable results than 0.5 mg in studies. Timing relative to your target bedtime matters as much as the dose, per the CDC.
Is it better to nap or stay awake after landing?
The CDC states that staying awake until local bedtime and eating at local mealtimes is more effective for resetting the clock than extensive daytime napping; the Sleep Foundation adds that any nap should be kept to about 30 minutes and finished at least eight hours before the planned local bedtime.
How long does jet lag actually last?
A 2019 Frontiers in Physiology review estimates full adaptation around day 4 for a 3-hour time shift, day 6 for a 6-hour shift, and days 7–8 for a 9-hour shift; the Sleep Foundation more generally describes jet lag as lasting from a few days to a few weeks.
Should I try to adjust my schedule for a very short trip?
No — for stays of two days or fewer, the CDC Yellow Book suggests keeping your home time-zone sleep schedule instead of trying to adapt to the destination, since the body will not have time to resynchronize before you head home.
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