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Jet lag

Jet lag
Literature review current through: May 2024.
This topic last updated: Oct 17, 2023.

INTRODUCTION — Air travel allows individuals to traverse time zones faster than the internal clock, or circadian rhythm, can adjust. This results in desynchrony between the external light-dark cycle and the endogenous circadian rhythm. Jet lag ensues, which manifests as impaired alertness during the desired wake time and/or difficulty sleeping during the allotted time for sleep at the destination.

This topic reviews the underlying pathophysiology, clinical features, evaluation, and treatment of jet lag. Other circadian rhythm sleep-wake disorders are reviewed separately. (See "Overview of circadian rhythm sleep-wake disorders".)

EPIDEMIOLOGY — The prevalence of jet lag is unknown [1]. When international business travelers were surveyed, almost 70 percent reported that jet lag was present "fairly often" or "always" [2]. The impact of age and sex on the likelihood of developing jet lag has not been clearly defined [3], although older adults may be less likely to experience symptoms of jet lag [4,5].

PATHOPHYSIOLOGY — Circadian rhythms are the near 24-hour endogenous processes that allow an organism to react in an appropriate manner to environmental light-dark changes caused by the earth's rotation every 24 hours. One of the most obvious outputs of the circadian timing system is the sleep-wake cycle, which typically aligns to the light-dark cycle.

The circadian rhythm of sleep and wake is paralleled by the secretion of melatonin and oscillation of core body temperature (CBT):

In individuals with "normal" circadian phase, melatonin begins to rise in dim light approximately two hours prior to habitual sleep onset. The initiation of melatonin secretion is referred to as dim light melatonin onset (DLMO) and is associated with a drop in CBT, which coincides with a decrease in alertness.

The decrease in circadian alertness, combined with an elevated sleep need or homeostatic sleep drive from prior wakefulness, results in a high propensity for sleep during the nighttime hours [6].

Melatonin peaks just before the nadir of CBT (CBT minimum), typically about seven hours after DLMO and about three hours prior to habitual sleep offset. The low circadian alerting signal helps to maintain sleep as the homeostatic sleep drive dissipates.

In the morning, melatonin decreases back to undetectable levels and CBT begins to rise. The increasing circadian alerting signal, combined with the low homeostatic sleep drive, promotes wakefulness.

The circadian alerting signal increases throughout the day to oppose the growing homeostatic sleep drive, providing roughly 16 hours of consolidated wakefulness (figure 1) [6].

The circadian timing system, although inherent and set genetically, is modifiable. Zeitgebers (literally "time givers" in German) align or entrain the internal clock, which cycles every 24.2 hours on average in humans [7,8], to the 24-hour day. Bright light is the most potent stimuli to entrain circadian phase, though other zeitgebers include exercise, meals, and social contact [9-11].

The effect of light is dependent on the time of exposure in reference to endogenous circadian phase (figure 2). Bright light after the CBT nadir (in the early morning in normally entrained individuals) moves the circadian rhythm earlier (phase advance), and bright light after DLMO and prior to the CBT nadir (in the evening in normally entrained individuals) moves the circadian rhythm later (phase delay) [12]. Bright light produces the largest phase shifts when delivered during the biological night, when melatonin is secreted [13].

Exogenous melatonin can also shift the circadian clock (figure 2). The action of melatonin on the circadian timing system depends on when it is given [14]. When dosed in the late afternoon/early evening, melatonin advances the circadian rhythm; when taken in the morning, it produces phase delays [15]. Melatonin also has direct sedative effects. The phase shifting [16] and sedative effects [17] of melatonin are greatest at a time other than when it is naturally being secreted by the pineal gland (ie, during the biological day) [16,17].

Although the circadian clock is modified by bright light, phase shifts do not occur instantaneously after a change in the light-dark cycle precipitated by air travel but can take several days or more to become entrained to the new time zone. Therefore, the internal clock will remain set to the time of origin immediately after the change in light-dark cycle. The degree of desynchrony between the internal clock and external light dark cycle depends on the number of time zones crossed.

CLINICAL FEATURES — Clinical symptoms of jet lag occur one to two days after travel across at least two time zones and include disturbed sleep, excessive daytime sleepiness, generalized fatigue, somatic symptoms, and impaired daytime functioning [1].

Insomnia — Insomnia caused by jet lag is manifested by difficulties with both sleep onset and maintenance. These symptoms result from the overlap of high circadian alerting signal with the desired time for sleep. Travel circumstances and unfamiliar surroundings further exacerbate insomnia in some individuals.

Excessive daytime sleepiness — Excessive daytime sleepiness occurs due to the overlap of high sleep propensity with the desired time for wake in the new time zone. Accumulated sleep debt related to unsuccessful attempts to sleep when the circadian system is promoting alertness also contributes to daytime sleepiness [18].

Somatic symptoms — The most common somatic symptoms of jet lag are gastrointestinal, including decreased appetite and constipation [19]. These symptoms may be due to food consumption out of alignment with the circadian timing system [10]. Jet lag may result in poor mood [19] and can exacerbate underlying psychiatric disorders [20].

Impaired performance — Impaired cognitive and physical performance in jet lag result from decreased alertness and circadian misalignment [19,21]. Specific cognitive functions that may be impaired include introspection, emotional regulation, and decision-making [22]. Despite known decrements in physical performance with jet lag, jet-lagged athletes do not appear to be at increased risk of injury [23]. However, given the performance ramifications, jet lag continues to garner attention in athletics [24].

Clinical course — Without targeted treatment, the circadian timing system will adjust to destination time by roughly one time zone per day for eastward travel and 1.5 time zones per day for westward travel [25]. In addition to distance traveled, the severity of jet lag is influenced by multiple factors [3,19,20]:

Direction of travel (eastward travel is more difficult to adapt to than westward travel)

Ability to sleep during travel

Presence of and access to circadian zeitgebers at the destination (eg, light) (see 'Pathophysiology' above)

Individual differences in the internal timing system

Travel conditions (eg, reduced mobility, air quality and pressure, intake of alcohol and caffeine)

Although self-limited, jet lag can have significant repercussions in those who require high levels of performance immediately after international travel (eg, pilots, athletes, business travelers, military personnel).

Limited data suggest that individuals who repeatedly undergo transmeridian air travel may have an increased risk for adverse long-term health outcomes, including memory impairment [26], reproductive dysfunction in women [27-30], and possibly cancer [31,32]. Changes in intestinal microbiota during jet lag may also have the potential to promote obesity and metabolic dysfunction [33]. A large cohort that evaluated health conditions in over 5000 flight attendants demonstrated increased risk of cancer, sleep disorders, fatigue, and depression; however, other occupational factors independent of jet lag may contribute to these findings [34].

DIAGNOSIS — The diagnosis of jet lag is based on clinical assessment. Diagnostic criteria put forth by the International Classification of Sleep Disorders, Third Edition, Text Revision (ICSD-3-TR), include the following features [1]:

Insomnia or excessive daytime sleepiness, accompanied by a reduction of total sleep time, associated with jet travel across at least two time zones

Impaired daytime function, general malaise, or somatic symptoms (eg, gastrointestinal disturbance) within one to two days after travel

The sleep disturbance cannot be explained by another current sleep disorder, medical disorder, mental disorder, or medication/substance use

Wrist actigraphy and objective assessments of circadian phase such as core body temperature (CBT) and melatonin assays have been used as an outcome measure to determine treatment effect in jet lag studies. Due to the transient nature of this disorder, however, these serial tools have minimal utility in the clinical setting. (See "Overview of circadian rhythm sleep-wake disorders", section on 'Diagnostic tools'.)

Jet lag questionnaires have been developed but not adopted for clinical use [35].

DIFFERENTIAL DIAGNOSIS — Jet lag may be confused with travel fatigue. Travel fatigue is a constellation of symptoms including fatigue, confusion, headache, and travel weariness due to disruption of normal sleep routine, dehydration, restricted space, and stress of travel [19]. This is distinct from jet lag, as it is not dependent on the number of time zones crossed (eg, it can occur after long distance north-south air travel) and resolves after a good-quality sleep period [19].

MANAGEMENT — The treatment goal in jet lag is to improve symptoms of insomnia and excessive daytime sleepiness. The strategy for treatment is to align the patient's internal circadian phase with the new light-dark cycle in the destination time zone. In turn, this will result in improved sleep and alertness at the desired times. Although this adjustment will occur naturally without treatment, strategic use of light and melatonin can hasten this process (table 1).

Other jet lag treatments (eg, caffeine, napping, hypnotics) focus directly on the symptoms, without an attempt to promote adjustment of the endogenous circadian timing system.

Short trips (less than three days) — Trips lasting only one or two days are generally too short to expect adjustment to the destination time zone. In fact, limited data suggest that staying on origin time, rather than attempting to adjust to the destination time, may help to reduce jet lag [36,37]. Caffeine and hypnotic use may directly mitigate symptoms, although risk of adverse effects must be weighed carefully with potential for benefits. (See 'Symptomatic measures' below.)

Longer trips (three or more days)

Eastward travel, up to seven time zones — Eastward travel requires an advance of the circadian timing system to adjust to the new time zone, and appropriately timed light exposure and exogenous melatonin can hasten adjustment [16,38]. We suggest using both strategies for eastward travel, as the combination may result in larger circadian phase shifts than use of one intervention alone [39,40].

Timed light exposure — The proper timing of both light and melatonin for eastward travel is based on circadian physiology (figure 2) and illustrated by the figure (figure 3). Appropriately timed light exposure can result in phase advances of about 1.5 hours per day [41]. Treatment timing should therefore be adjusted daily, one hour earlier per day with eastward travel [42]. (See 'Upon arrival' below.)

Several web- and mobile-based applications may be used to guide timing of interventions for jet lag [43,44]. While not validated in clinical studies, at least one uses mathematical modeling to determine the light-dark schedule that will most rapidly align circadian phase to the destination time zone [45,46]. In the author's experience, these tools can be helpful for predicting the personalized timing of treatments as described below.

Prior to travel — For motivated individuals, bright light therapy may be started up to three days prior to departure, in an attempt to advance the circadian phase and reduce the degree of desynchrony upon arrival at the destination.

The source of light can be either natural outdoor daylight (weather and season permitting) or a light box. Individuals should wake up about one hour earlier than their usual wake time and seek exposure to bright light for at least one hour. This is repeated daily for up to three days prior to departure, successively advancing the wake time. Bedtimes should be similarly advanced one hour earlier each night if possible.

Two studies evaluated the effects of advancing the sleep-wake cycle by one to two hours per day in conjunction with 3.5 hours of morning bright light (3000 to 5000 lux, either continuous or intermittently pulsed) for three days prior to simulated eastward travel [47,48]. Advancement of circadian phase was nearly two hours per day with bright light as determined by dim light melatonin onset (DLMO) [47,48].

Upon arrival — Upon arrival at the destination after eastward travel, strategic light exposure and light avoidance can be timed to help advance the internal circadian phase. The best source of light is direct, outdoor sunlight. A light box can also be used.

For trips crossing three to five time zones, this generally means avoiding bright daylight first thing in the morning at the destination, and then seeking out several hours of bright light beginning mid- to late-morning. For trips crossing six or seven time zones, bright light should generally be avoided during the morning on the day of arrival and sought out in the early afternoon. In both cases, light exposure can then be shifted gradually earlier on successive days.

For patients interested in timing light exposure more precisely and gradually advancing the timing for the first several days at the destination, the timing can be calculated based on circadian physiology, as illustrated in the figure (figure 3). The key is to know that core body temperature (CBT) minimum occurs about three hours before usual wake-up time (ie, 4:00 AM for someone who typically wakes up at 7:00 AM), and then use the CBT minimum to time light exposure at the destination. For an individual with a CBT minimum at 4:00 AM in New York who travels to London, for example, CBT minimum will occur in London at 9:00 AM (five hours ahead of New York). Upon arrival in London, the individual should seek several hours of bright light exposure beginning after 9:00 AM (CBT minimum) and avoid bright light before 9:00 AM. On each successive day, bright light avoidance and exposure should begin one hour earlier, until the desired wake up time is reached.

In experimental studies assessing the effects of light alone, bright light (2000 to 5000 lux), when timed appropriately, can shift circadian phase in response to simulated eastward and westward travel [49,50]. Appropriately timed light exposure as low as 380 lux is also capable of significant advancement of circadian phase (five hours) in response to simulated eastward travel of five time zones [51]. As a reference, bright daylight on a sunny day is at least 10,000 lux.

Studies of light exposure as a treatment for jet lag in real-world settings have had mixed results.

One small, randomized study of three hours of light exposure at 11:00 AM destination time after eastward travel from Tokyo to San Francisco demonstrated that bright light (3000 lux) improved nighttime sleep efficiency compared with more dim light [52]. A similar study comparing bright light (2000 lux) with more dim light for two to three hours upon awakening after traveling from Asia to California failed to show any differences between groups [53].

In a randomized trial of 22 female soccer players traveling eastward five to eight time zones, participants were exposed to a single dose of 2500 lux artificial light at 3:30 PM to 4:30 PM on the day of arrival and advanced by one hour each day for the next three days [54]. The bright light group experienced a small but significant decrease in jet lag scores compared with the control group. The small difference seen in jet lag scores in this study may have been due to the fact that the light therapy was not delivered at an optimal segment of phase response curve that would generate maximal circadian phase advance. Additionally, no restrictions were placed on the control group in terms of natural outdoor light exposure.

Timed melatonin — To help advance the circadian phase after eastward travel across up to seven time zones, the appropriate timing of melatonin is in the evening, at the desired destination bedtime. Taking melatonin at bedtime upon arrival helps with phase advance (figure 3) and also takes advantage of the possible sedative effects of melatonin for some individuals. This timing will fall in the advance portion of the phase response curve to melatonin, before dim light melatonin onset (DLMO) (figure 2). (See 'Pathophysiology' above.)

We suggest starting melatonin on the evening of arrival and continuing for up to five days. Doses used have ranged from 0.5 to 10 mg; in our experience, 3 mg of melatonin is sufficient, and some clinicians find immediate formulations more effective than delayed release.

A systematic review of 12 placebo-controlled trials of melatonin found heterogeneous methodology, using a range of melatonin strengths (0.5 to 10 mg) and dosing as early as three days prior to departure and as long as five days after arrival in the destination [3]. Ten of the 12 studies demonstrated an improvement in jet lag symptoms. Studies that assessed sleep measures demonstrated improved sleep duration and quality with both subjective and objective measures. In the few studies that measured circadian phase, the rhythms of cortisol and oral temperature entrained to destination time three to four days more quickly in individuals taking melatonin as compared with placebo. Most studies assessed the use of melatonin during eastward travel. Only one study compared different doses and formulations of melatonin and found that immediate-release formulation may be of greater benefit than slow release [55].

When compared with placebo in studies on jet lag, melatonin does not appear to confer a significant risk of side effects [3]. Regulation of melatonin products varies by country; in the United States, melatonin is considered a dietary supplement and can be purchased without a prescription.

Like melatonin, melatonin receptor agonists (eg, ramelteon, tasimelteon) are also capable of promoting sleep and shifting circadian phase [56-59]. Given the widespread availability and low cost of melatonin, however, we see no compelling reason to use a melatonin agonist for jet lag, pending further studies.

Available data on melatonin receptor agonists for jet lag include a randomized trial of ramelteon (1 mg) in 110 healthy adults flying eastward across five time zones [60]. Ramelteon reduced the latency to persistent sleep by approximately 10 minutes compared with placebo but did not shift circadian phase [60]. Although adverse events were similar between ramelteon and placebo, individuals in the ramelteon group performed significantly worse on memory testing on the fourth day of treatment.

Hypnotics — As a symptomatic measure, benzodiazepines and nonbenzodiazepine benzodiazepine receptor agonist (BzRA) medications are effective for insomnia associated with jet lag. We do not recommend the routine use of these drugs, however, based on the potential side effects, with particular concern for next-day performance deficits.

A systematic review identified nine studies that investigated the effect of hypnotics, either benzodiazepines or nonbenzodiazepine BzRAs, on jet lag symptoms [3]:

The benzodiazepines used were temazepam (10 to 20 mg), midazolam (7.5 mg) [61], and triazolam (0.5 mg). In placebo-controlled trials, both temazepam (20 mg) [62] and midazolam [61] improved subjective sleep quality with eastward travel greater than eight time zones. Neither triazolam nor temazepam (10 mg) [63] conferred any benefit over placebo during westward travel [3].

The nonbenzodiazepine BzRAs used were zolpidem and zopiclone. In a randomized trial in 133 adults, zolpidem (10 mg, a dose no longer recommended in women and older adults) improved self-reported total sleep time, sleep efficiency, and awakenings relative to placebo in the context of eastward travel [64]. In a smaller trial, zopiclone (7.5 mg) improved objectively recorded sleep duration but not jet lag scores during westward travel [65].

Several trials have compared hypnotics with melatonin, with mixed results. In one trial, 137 adults traveling eastward on an overnight flight were randomly assigned to receive in-flight zolpidem (10 mg), melatonin (5 mg), or both; treatment was continued for four nights upon arrival [66]. Compared with melatonin, zolpidem was associated with improved jet lag scores and better subjective sleep duration and quality. The combination of melatonin and zolpidem was no better than zolpidem alone, but side effects were increased. In another study of eastward travel, zopiclone and melatonin resulted in equally effective improvements in subjective and objective sleep duration and quality during eastward travel [67].

Care must be taken with use of hypnotics during air travel due to potential side effects, which may be greater when melatonin is also being used [66]. Clinicians should be aware of dosing precautions in women and older adults for certain drugs such as zolpidem, as well as class-wide risks of next-day impairments in cognition, motor performance, and driving. (See "Pharmacotherapy for insomnia in adults", section on 'Benzodiazepine receptor agonists'.)

Caffeine and other stimulants — Judicious use of caffeine is generally safe and can help offset daytime sleepiness associated with jet lag, but benefits may be outweighed by sleep disruption in some cases. After eastward travel, caffeine in its slow release pill form improved objective sleepiness compared with melatonin and placebo [68] and also hastened circadian entrainment [69]. However, sleep onset latency and awakenings increased [68].

Armodafinil, a wake-promoting agent, may be an option for patients who require alertness and have not had sufficient results with behavioral strategies and caffeine on prior trips. This is not an FDA-approved indication, and cost may be prohibitive in many patients. Armodafinil was studied in a randomized trial of 427 adults with a history of jet lag traveling from the United States to France [70]. Compared with placebo, objective daytime sleepiness and perception of jet lag symptoms were improved in patients assigned to armodafinil (taken every morning for three days). However, headache and nausea were common at the effective dose (150 mg). Additionally, armodafinil is not approved for an indication of jet lag; therefore, off-label use and lack of insurance coverage may be cost prohibitive.

Napping — Napping is a reasonable strategy to combat decreased alertness due to sleep loss. To avoid nighttime sleep disruption, naps should be less than 30 minutes long and at least 8 hours before the anticipated bedtime.

Napping has not been widely investigated in jet lag. In one study of simulated eastward travel across five time zones, a 20-minute nap did not improve performance and lengthened sleep onset latency of the nighttime sleep bout [71]. Notably, sleep quality during in-flight napping may be suboptimal in upright versus recumbent seated positions [72].

Eastward travel, eight or more time zones — With travel of eight or more time zones eastward, most individuals will find it easier to delay, rather than advance, their circadian phase once they arrive in the new time zone. This generally means seeking out morning light at the destination and avoiding bright light in the late afternoon and evening for the first few days after arrival.

The rationale for this practice is the observation that the circadian rhythm delays rather than advances in many individuals traveling eastward eight or more time zones [73-75]. This phenomenon is known as antidromic shifting and is due to the occurrence of CBT minimum at a time of day when bright light is ample in the delay portion of the phase response curve to bright light (figure 2).

Westward travel — Westward travel requires a delay of the circadian timing system to adjust to the new time zone. Appropriately timed light exposure can achieve phase delays of about 2.5 hours per day [41,49]. Melatonin is generally not needed for westward trips crossing up to 12 time zones but may provide some additional benefit for trips crossing more than 12 time zones.

Timed light exposure — Upon arrival at the destination after westward travel, light exposure and avoidance can be strategically timed to help delay the internal circadian phase. The best source of light is direct, outdoor sunlight. A light box can also be used.

The proper timing of bright light for westward travel depends on circadian physiology (figure 2) and is illustrated by the figure (figure 4). As with eastward travel, the key is to know that CBT minimum occurs three hours before usual wake-up time (ie, 4:00 AM for someone who typically wakes up at 7:00 AM), and then use the CBT minimum to time light exposure at the destination. For an individual with a CBT minimum at 4:00 AM in New York who travels to Honolulu, for example, CBT minimum will occur in Honolulu at 11:00 PM (five hours behind New York). Upon arrival in Honolulu, the individual should seek out bright light exposure in the evening by attempting to stay awake in bright indoor light until bedtime at the destination. After 11:00 PM (CBT minimum), bright light should be avoided, which is easy given the natural light dark cycle.

As with eastward travel, studies testing the effects of a light intervention after westward travel have had mixed results. As examples:

In one study, 20 individuals traveling westward from Zurich to New York were randomly assigned to receive bright light (3000 lux) or a dim light control for three hours at 7:00 PM on the first two evenings after arrival in New York [73]. Those who received bright light had a significant circadian phase delay compared with the dim light control group, but there were no differences in sleep, mood, performance, or jet lag symptoms between the groups.

Another study made use of light-emitting and light-blocking sunglasses to strategically time light exposure during simulated westward travel from Sydney, Australia to London, England [76]. During travel and for two days post-travel, blue-green spectrum light (508 lux) was delivered for three hours prior to 5:00 AM origin time, and light-blocking sunglasses were worn from 5:00 AM to 8:00 AM origin time. This intervention, along with sleep hygiene, improved vigor, jet lag symptoms, and mood scores compared with control. There were no differences in performance or objectively recorded sleep measures between the two groups.

Timed melatonin — Because circadian rhythm delays are usually easier than advances, melatonin is typically unnecessary for westward travel crossing up to 12 time zones.

For westward travel crossing more than 12 times zones, melatonin can be taken at bedtime on the evening of arrival and continuing for up to five days. Doses used have ranged from 0.5 to 10 mg; in our experience, 3 mg is sufficient.

A systematic review of placebo-controlled trials of melatonin for jet lag identified two trials in which melatonin was studied in the context of long-haul westward travel. In both small trials, melatonin was associated with an improvement in jet lag symptoms and sleep [77,78]. The beneficial effects were likely due to the fact that travel was over at least 12 time zones, which placed melatonin dosing in both the phase delay portion of the melatonin phase response curve and during a time when endogenous melatonin is not secreted.

Symptomatic measures — Use of hypnotics for insomnia is not suggested and typically unnecessary for westward travel, particularly when crossing less than 12 time zones. In two randomized trials, neither triazolam nor temazepam (10 mg) conferred any benefit over placebo during westward travel [3,63]. In a separate trial, zopiclone (7.5 mg) improved objectively recorded sleep duration but not jet lag scores during westward travel [65]. Side effects of hypnotics may be increased with concurrent melatonin use. (See 'Hypnotics' above.)

As with eastward travel, short naps and judicious use of caffeine can help offset daytime sleepiness associated with jet lag after westward travel, but benefits may be outweighed by sleep disruption in some cases. (See 'Caffeine and other stimulants' above and 'Napping' above.)

Notably, a meta-analysis determined that apart from melatonin supplements, the use of functional foods, beverages, and supplements for jet lag is not supported by the available literature [79].

SUMMARY AND RECOMMENDATIONS

Clinical features – Jet lag results in excessive daytime sleepiness and/or insomnia along with generalized fatigue and somatic symptoms in the context of transmeridian travel. The symptoms of jet lag result from the misalignment of the endogenous, circadian timing for sleep and wake with the desired timing of sleep and wake in the destination time zone. (See 'Pathophysiology' above and 'Clinical features' above.)

Jet lag tends to be more severe with travel across a greater number of time zones and with eastward compared with westward travel. (See 'Clinical course' above.)

Diagnosis – Jet lag is diagnosed by clinical history when the following are present: insomnia or excessive daytime sleepiness associated with a reduction of total sleep time coinciding with jet travel across at least two time zones; impaired daytime function, general malaise, or somatic symptoms that begin within two days of travel; no other disorder explains the sleep disturbance. (See 'Diagnosis' above and 'Differential diagnosis' above.)

Management – For motivated patients, treatment of jet lag is aimed at accelerating adjustment to the new time zone with strategically-timed bright light and exogenous melatonin, along with symptomatic measures to help mitigate symptoms of excessive daytime sleepiness and insomnia (table 1). (See 'Management' above.)

The optimal timing of light exposure and melatonin is determined by the direction of travel and the number of time zones crossed. The best source of light is direct, outdoor sunlight. A light box can be used, although this is impractical for most travelers.

Eastward travel, ≤7 time zones – For eastward travel across up to seven time zones, we suggest strategically-timed light exposure and melatonin rather than either therapy alone (Grade 2C). The precise timing of light exposure to promote advancement of the circadian phase is detailed in the text and the figure (figure 3). In general, this means avoiding bright light first thing in the morning and seeking bright light mid- to late-morning upon arrival at the destination. For motivated individuals, light therapy may be started up to three days prior to departure. (See 'Timed light exposure' above.)

Melatonin should be taken at bedtime starting on the evening of arrival and continuing for up to five days. Doses used have ranged from 0.5 to 10 mg; in our experience, 3 mg is sufficient. (See 'Timed melatonin' above.)

Eastward travel, >8 time zones – For eastward travel across eight or more time zones, most individuals will find it easier to delay, rather than advance, their circadian phase to adjust to the new time zone. This generally means seeking out morning light at the destination and avoiding bright light in the late afternoon and evening for the first few days after arrival. (See 'Eastward travel, eight or more time zones' above.)

Westward travel, ≤12 time zones – For westward travel across up to 12 time zones, we suggest strategically-timed light exposure rather than melatonin or a combination of the two (Grade 2C). The precise timing of light exposure to promote delay of the circadian phase is detailed in the text and the figure (figure 4). For westward travel across more than 12 time zones, we also suggest melatonin at bedtime (Grade 2C). (See 'Westward travel' above.)

Benzodiazepines and nonbenzodiazepine benzodiazepine receptor agonist (BzRA) medications have demonstrated efficacy in treating insomnia associated with jet lag. However, potential benefits must be weighed against side effects, in particular a concern for next-day performance deficits. (See 'Hypnotics' above.)

Judicious use of caffeine is generally safe and can help offset daytime sleepiness associated with jet lag, but benefits may be outweighed by sleep disruption in some cases. Short naps (<30 minutes) at least eight hours prior to bedtime may also help alertness without disrupting nighttime sleep. (See 'Caffeine and other stimulants' above and 'Napping' above.)

ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Andrew Herxheimer, MB, FRCP, who contributed to an earlier version of this topic review.

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