West 1.5 Hours a Day, East 1 Hour: US CDC Jet Lag Guidance

Jet lag is a disturbed sleep pattern after a long flight. The US Centers for Disease Control and Prevention (CDC) Travelers' Health page says jet lag usually occurs when you cross more than three time zones. The 2026 edition of the CDC Yellow Book, written for healthcare professionals, gives an average adaptation rate of about 1.5 hours a day travelling west and about 1 hour a day travelling east.

In the first days of an overseas business trip, cognitive performance may not be at its best. The Yellow Book lists cognitive impairment, daytime sleepiness and impaired daytime function as effects of jet lag. This article draws on the CDC, the UK National Health Service (NHS) and a BMJ Clinical Evidence review to set out what can be done before and after a flight. Information is as of November 2026.

Flying east is harder to adapt to than flying west

The Yellow Book explains that the body clock runs slightly longer than 24 hours, so delaying the daily rhythm (flying west) is easier than advancing it (flying east). A 2008 BMJ Clinical Evidence review also states that jet lag tends to be worse after eastward than westward flights.

It follows that, on the same round trip, the outbound and return legs may differ in difficulty, so flight direction is worth considering when planning an itinerary.

Start adjusting your routine two to three days before departure

The CDC Travelers' Health page advises starting to shift your body clock towards the destination time zone a few days before travel. The approach depends on direction:

• Travelling west: go to bed one to two hours later than usual.
• Travelling east: go to bed one to two hours earlier than usual.
• The Yellow Book is more specific: in the 2 to 3 days before departure, shift sleep by about 1 hour a day towards the destination time zone.

The NHS also advises resting well before travel and starting to move bedtime and wake-up time towards the destination time zone.

Light can help adjust the body clock

The CDC Travelers' Health page says only briefly that staying in well-lit areas during the day after arrival might help. The NHS also says that going outside in daylight helps the body clock adjust.

The detail on timing comes from the Yellow Book: morning light shifts the body clock earlier, and evening light shifts it later. For eastward travel, it advises seeking bright light early in the day and avoiding light in the evening.

This magazine reports only the Yellow Book's eastward example and does not extend it into a general rule for every journey. Readers crossing many time zones, or who are particularly sensitive to jet lag, should consult a doctor first.

After arrival: keep naps short and stop caffeine early

• The NHS advises adopting the new time zone as soon as possible, using an alarm to avoid oversleeping, and avoiding daytime sleep.
• If you cannot stay awake, the CDC Travelers' Health page suggests naps of no more than 15 to 20 minutes. The Yellow Book says naps of 20 to 30 minutes can help sustain alertness, but longer daytime naps may disrupt night-time sleep.
• The Yellow Book advises stopping caffeine about 6 hours before bedtime.
• The Yellow Book advises avoiding antihistamines and long-acting benzodiazepines, because they can worsen cognitive impairment and raise the risk of falls.

If jet lag keeps causing difficulty, the CDC Travelers' Health page advises talking to a doctor about medicine or other sleep aids.

Melatonin: the evidence and its limits

The CDC Travelers' Health page does not mention melatonin; the relevant content appears only in the Yellow Book. The Yellow Book says melatonin taken when the body's own melatonin is at its peak (body clock time 12 a.m. to 5 a.m.) is less effective. It also advises against high doses. In addition, melatonin is not regulated by the US Food and Drug Administration (FDA), so the amount stated on a label may differ from what the product contains.

Other bodies are more cautious. The NHS says it does not recommend melatonin tablets for jet lag because there is not enough evidence that they work. The 2008 BMJ review rated the evidence that melatonin reduces subjective jet lag as low quality, with a larger effect on eastward flights. It also warns that people with epilepsy, and those taking warfarin or other oral anticoagulants, should not use it without medical supervision.

This article recommends no dose. Whether and how to use melatonin should be discussed with a doctor first.

Consider leaving two days before important events

The CDC Travelers' Health page suggests considering arriving at least 2 days before any important event.

Taken together, the advice is to adjust your routine before departure, pay attention to daylight on arrival, and allow time to adapt before important events.

Note on source dates

The CDC Travelers' Health page was last reviewed on 6 October 2022. The web page for the 2026 Yellow Book is dated 23 April 2025. The BMJ Clinical Evidence review was published in 2008, so its evidence is older. This article is general health information; it is not a diagnosis or medical advice.

Prices and details correct as of November 2026

Compiled by the F50 Editorial Team from public sources, for general reference only and not professional advice. Details are correct as of the publication date and may change.