How to Reduce Jet Lag

Jet lag happens when your body clock stays set to your home time zone after you arrive in a new one. The clock controls when you feel sleepy and when you feel alert, so after a long flight you may wake at 3 a.m. and feel drowsy at lunch. Researchers describe the clock as a roughly 24-hour rhythm that light and other cues reset each day.

Two tools do most of the work: light exposure and melatonin, a hormone the body releases in the evening to signal night. The right timing depends on flight direction. Eastward trips are harder to adjust to than westward ones, and the steps that help most before departure differ from those that help after you land.

Why eastward trips are harder

The direction of travel decides how much work your clock has to do. Most people’s internal rhythm runs slightly longer than 24 hours, so the clock finds it easier to delay, which means staying up later, than to advance, which means going to sleep earlier. A flight from New York to London moves you forward in time, so your body needs to advance, and that is the harder adjustment. A flight from London back to New York moves you backward, so your body needs to delay.

After eastward travel, people more often struggle to fall asleep at the new bedtime. After westward travel, they more often wake too early. Harvard Health notes that crossing one or two time zones is usually manageable, while longer multi-zone trips are much harder. The Chronobiology International study on timed light and the PMC review of flight interventions both build their advice around this asymmetry. Eastward travelers should plan more preparation, and westward travelers have the simpler job.

Using light at the right time

Light is the strongest timing signal for the body clock, and it works in a predictable way. Light received in the roughly 12 hours before the body’s temperature minimum, called CBTmin, delays the clock. Light received in the roughly 12 hours after CBTmin advances it. The largest shifts come from light 3 to 6 hours on either side of CBTmin. CBTmin is the low point of the body’s internal temperature cycle, and it sits at a fairly predictable time for a given sleeper. The PMC review uses a person who sleeps from 23:00 to 07:00 as its example, with CBTmin around 04:00. For that sleeper, light in the three to six hours after 04:00 advances the clock, and light in the three to six hours before it delays the clock.

For an eastward trip, that means bright morning light at the destination is the useful exposure, because it pushes the clock earlier. For a westward trip, evening light at the destination delays the clock in the right direction. Avoiding bright light late in the evening before an eastward departure keeps the clock from moving the wrong way. The Arendt review of jet lag management supports these directions, so the direction of each rule is the dependable part.

Light also has limits as a stand-alone remedy. The PMC review describes the idea that maximizing sunlight in a new time zone helps jet lag as a common anecdotal belief. The timing of light relative to CBTmin, meaning when the light arrives, matters more than the total amount of daylight you get. No study measures how much recovery time timed light saves in real travelers, so light is best treated as a timing tool rather than a guaranteed fix.

Melatonin: what the trials show

Melatonin is the best-studied supplement for jet lag, and its benefit appears most clearly on eastward trips that cross several time zones. The Cochrane-based commentary by Caspi (2004) reports a weighted mean jet-lag score of 25 after melatonin and 48 after placebo, scored from 0 to 100, with higher scores meaning worse symptoms. In one eastward transatlantic trial in that commentary, 16 of 24 placebo recipients (67%) had jet lag, compared with 4 of 22 recipients (18%) who took 5 mg of melatonin. The AAFP summary of the Cochrane review gives a number needed to treat of two, meaning that about one person in two taking melatonin benefits who would not otherwise. The benefit appears larger with more time zones crossed and smaller for westward flights.

The commentary also contains a pooled effect figure that does not agree with its own raw scores, and the figure appears to be a transcription error. Check the original Cochrane review before citing a pooled number.

Melatonin timing is the harder question. The timing rule is consistent: taken in the late afternoon or early evening, hours before CBTmin, melatonin advances the clock, which suits eastward travel. Taken in the morning, after habitual wake time, it delays the clock, which suits westward travel. The AAFP recommends taking it at bedtime on the day of arrival and for the next two to five nights, and it warns that taking it early in the day can cause sleepiness and delay adaptation. For westward travel, some guides suggest a morning dose at the destination. The AAFP’s warning about daytime sleepiness applies to that approach too.

Dosing guidance is not settled. The AAFP reports that 0.5 to 5 mg was effective, that 5 mg worked best, and that doses above 5 mg showed no added benefit. A 2 mg slow-release formulation was relatively ineffective in those reviews. The Drugs.com monograph describes lower doses as adequate: 0.5 to 2 mg before departure, and 5 mg for up to four days after arrival. It also notes that studies use widely different regimens. Some product guides list ranges that differ from the trial doses. Because no regulator has approved melatonin for jet lag, the Caister paper notes that the United States treats it as a dietary supplement. A traveler who takes melatonin should ask a pharmacist or physician about the dose and about any interaction with medicines such as warfarin or anti-seizure drugs, since the AAFP summary cites case reports of harm in those groups.

Shifting sleep before you fly

Adjusting your sleep before the flight is the step with the most direct trial evidence for eastward travel. In a study of 28 healthy young adults, a three-day program moved habitual sleep earlier by about one hour per day while participants got bright light in the morning, and it advanced their circadian rhythms with little cost to sleep or alertness. The shift works because it moves the clock toward the destination before the trip starts, so less re-adjustment is needed after landing. The Penn CBTI document describes the same logic and says pre-flight shifts help most for eastward travelers.

A practical version of this plan looks like going to bed and waking up a little earlier each day for three days before departure, with bright light in the morning. Work with a realistic shift, since the study’s participants moved by about an hour per day. Trials have not shown whether this reduces real-world recovery time. The study’s authors speculated that more days could eliminate jet lag, but they did not test that idea.

Eastward shifts are hard to hold. In a 1999 study of six people after an eight-hour eastward flight, four had advanced by day five, one had delayed, and one had not shifted. Some travelers move in the wrong direction, a pattern researchers call an antidromic shift. A medRxiv preprint that has not been peer reviewed suggests that advances longer than about seven hours may trigger that response. A simulation study found that forcing wakefulness on arrival made a phase advance more common. Simulations are not measurements of real travelers, so treat that finding as direction rather than outcome.

The Arendt review calls pre-flight adjustment the most effective way to avoid jet lag, but it also says the adjustment takes time and commitment. The tasimelteon trial found that timed bright light before travel moves the clock in the desired direction, but that trial enrolled people with a clinical circadian disorder rather than typical travelers, and it describes the approach as requiring high motivation and strict compliance.

Caffeine, alcohol, and sleep on the plane

Caffeine helps alertness but can also cost you sleep. A systematic review of 13 trials in people with jet lag or shift-work disorder found that caffeine improved several cognitive measures, including attention, memory, and reasoning, compared with placebo. The eastbound studies in that group used 300 mg of slow-release caffeine. One reported faster hormonal adjustment with lower cortisol than placebo, and a follow-up found objectively reduced daytime sleepiness. The 2002 eastbound flight trial found that slow-release caffeine reduced daytime sleepiness but had some unwanted effects on sleep, while melatonin improved sleep without reducing sleepiness objectively. Those trials were small and tested only eastbound travel. A practical rule drawn from the sleep guidance is to use caffeine in the morning and early afternoon at the destination and to stop it in the afternoon and evening. The cutoff protects night sleep, since caffeine can disrupt it.

Alcohol is a poor choice on a flight. It may help you fall asleep on the plane, but it increases dehydration and disrupts sleep later in the night. The PMC review says alcohol and caffeine both reduce sleep quality when taken a few hours before bed and advises travelers to avoid alcohol while treating jet lag. Harvard Health advises avoiding both caffeine and alcohol on flights because both promote dehydration, which worsens physical symptoms and disturbs sleep. Quantitative studies of alcohol and jet lag are lacking.

Sleeping on the plane is a judgment call with little controlled evidence. The 2002 trial authors noted that short-acting hypnotic drugs can help sleep during flights but carry side effects, and they did not test drug-free in-flight sleep. One claim holds that the body clock reads sleep as darkness, so sleeping while the destination is in daylight can push the clock the wrong way. No study tests this, so treat it as a plausible idea rather than an established rule. A practical approach is to sleep during the flight only when the timing lines up with the destination night, and to use the window seat and an eye mask to make sleep possible.

Hydration, meals, exercise, and naps

Hydration has no controlled evidence as a jet-lag remedy. Drinking water supports general health but does not reset the body clock. Harvard Health counts dehydration as a factor that worsens symptoms, so drinking water on a flight is a reasonable habit for physical comfort. Whether caffeine in moderate amounts counts against hydration is disputed, and the evidence does not settle it.

No evidence shows that meal timing changes jet lag, so eating on the destination schedule is a comfort choice, with no proven effect on jet lag. Exercise is similar. The guidance from Sleep Education recommends exercise before and after travel without naming a type, timing, or intensity, and no trial shows that exercise shifts the clock. A reasonable habit is light movement during the flight to ease stiffness, and avoiding hard exercise close to destination bedtime, which some guides say keeps travelers awake.

Naps after landing are another area where the common advice runs ahead of the evidence. Some guides say that naps longer than 20 minutes risk grogginess and deep sleep, but no study sets a nap length. A short nap in the early afternoon is a practical way to manage fatigue, while a long nap late in the day makes the first night harder.

Matching your plan to the trip length

The length of the trip and the number of time zones should set the scale of your plan. The PMC review says that adjusting sleep to the new time zone in the days before travel may help on trips longer than a week, and it does not appear useful for short trips. For a short trip, a traveler gains more from getting enough sleep the nights before departure and from light exposure at the destination than from a multi-day shift. Harvard Health suggests gradually moving bedtime toward the destination schedule on multi-zone trips, but it does not give a number of days or a number of minutes per day.

When planning, decide the direction first, then count the days you have. An eastward trip across several zones gives the strongest case for a three-day pre-flight shift and morning light at the destination. A westward trip gives more room to rely on evening light and late-night rest after landing. On a trip of a few days across one or two zones, light management and good sleep at the destination are usually enough.

Recovery time is harder to predict than the plan. A common rule of thumb is about one day of recovery per time zone, with large individual variation. Jet lag as a formal condition is defined in the sleep disorder classification as travel across at least two time zones, with excessive sleepiness or insomnia, and with symptoms that begin within roughly one to two days. The CDC Yellow Book entry on jet lag disorder covers the condition for travelers, and travelers with health conditions should check it before they plan a long trip.

Summary of the main steps

• Time light by direction: After eastward travel, seek bright light in the three to six hours after the body’s temperature low point, which the PMC review puts around 04:00 for a 23:00 to 07:00 sleeper. After westward travel, use evening light at the destination.
• Take melatonin at destination bedtime: The AAFP recommends a dose at bedtime on the day of arrival and for two to five more nights, with 0.5 to 5 mg studied and 5 mg working best. Ask a pharmacist or physician to check the dose, since no regulator has approved melatonin for jet lag.
• Shift sleep before an eastward flight: A trial of 28 healthy young adults advanced sleep by about one hour per day for three days, with morning bright light. Trips longer than a week benefit most from this step.
• Stop caffeine and alcohol early: Keep caffeine to the morning and early afternoon, and skip alcohol on the flight, since both disrupt sleep and alcohol adds to dehydration.
• Expect eastward trips to take longer: Eastward travel requires a bigger shift of the clock. In one small study, some travelers moved their clocks the wrong way after an eight-hour eastward flight.