You land and your body feels heavy, your head foggy — then at night you're wide awake. That's jet lag, and it isn't simple tiredness. It's your internal clock out of step with local time.
Which means “just push through” is slower than deliberately moving the clock.
1. How long it takes. The CDC gives different rates by direction — 1.5 hrs/day westward, 1 hr/day eastward. For an eight-hour shift that is about 5.3 days west and 8 days east (our calculation).
2. What to watch out for. In Korea melatonin is a prescription-only medicine; its approved indication does not include jet lag, and the 0.5–1 mg strength the CDC cites is not sold there at all.
3. How to start. Shift bedtime 1 hour a day for the 2–3 days before you fly, then time light by your own habitual wake time, not the clock on the wall.
The agency guidance reverses with direction
Search jet lag and you get a hundred tips. So we copied only what an agency actually writes.
The US Centers for Disease Control and Prevention states that jet lag “usually occurs when you travel across more than three time zones,” and gives pre-trip advice that runs in opposite directions depending on which way you fly.
The agency gives only four numbers.
① More than three time zones — when jet lag sets in
② More than three hours' difference → follow the destination's routines
③ Naps “no more than 15-20 minutes”
④ Arrive “at least 2 days before any important events”
Everything else is light — “it might help to stay in well-lit areas at your destination during the day.”
“Arrive two days early” is the most usable line here. The other three are about managing your body; this one is about how you build the itinerary.
The traveler page does not say why two days — but the CDC's clinician-facing Yellow Book does spell out the pre-trip schedule.
“Shifting sleep 1 hour later (for westward travel) or earlier (for eastward travel) per day in the 2–3 days prior to the trip may reduce the amount of time required to adjust to the destination time zone.”
— US CDC Yellow Book 2026, “Jet Lag Disorder”
So: 2–3 days out, one hour a day, later going west and earlier going east. The reason sits in the same sentence — to cut the time you need after landing.
Melatonin — a different story in Korea
Melatonin is absent from the traveler page. The Yellow Book does give a dose.
“Melatonin dosages vary, but 0.5–1 mg is often sufficient to produce a circadian shift. It is not recommended to take high-dose melatonin (>5mg) because this can cause excess melatonin to be present at the wrong time of day as it is metabolized.”
— US CDC Yellow Book 2026, “Jet Lag Disorder”
That sentence does not transfer to Korea. Melatonin sits on the supplement shelf in the US; in Korea it is a prescription-only medicine. The approval on file with the Ministry of Food and Drug Safety reads:
| Item | Korean approval (Circadin SR 2 mg) |
| Class | Prescription-only — not available over the counter |
| Indication | “Monotherapy for the short-term treatment of insomnia in patients aged 55 and over with poor sleep quality” |
| Dosing | “One tablet once daily after food, 1–2 hours before bedtime. May be taken for up to 13 weeks.” |
| Strength | 2 mg — larger than the 0.5–1 mg the CDC cites |
Three mismatches: jet lag is not an approved indication, the population is 55 and over, and the strength exceeds the CDC figure. So this article does not recommend melatonin for jet lag — in Korea it is a drug you discuss with a doctor. Buying it in the US is covered in drugstore part two.
Why eastward is harder
The human body clock naturally runs slightly longer than 24 hours, so going to bed later is easy and going earlier is hard.
| Direction | What your body must do · difficulty |
| Westward (e.g. Asia → Europe or US west) | Day gets longer → sleep later → easier |
| Eastward (e.g. Europe → Asia) | Day gets shorter → sleep earlier → harder |
| North–south (no time change) | Little jet lag, just travel fatigue |
The CDC puts numbers on that gap.
“westward travel is easier to adapt to than eastward travel, with an average rate of adaptation of 1.5 hrs/day for westward travel and 1 hr/day for eastward travel.”
— US CDC Yellow Book 2026, “Jet Lag Disorder”
Which means the familiar “one time zone per day” rule is only half right — it holds eastward only, and westward runs 1.5 times faster. Applied to eight hours: about 5.3 days west, 8 days east (our calculation). Nearly three days apart for the same eight hours.
So prepare in advance for eastward trips; westward can often be handled on arrival.
Light is your strongest tool
| Goal | Seek light / avoid light |
| Eastward (need earlier sleep) | Bright light in the local morning / avoid it in the evening |
| Westward (need later sleep) | Light in the local afternoon and evening / avoid strong early-morning light |
The CDC gives no clock times — because the anchor is your body, not the wall clock: “Exposure to bright light in the morning following the circadian nadir (approximately 2–4 hours prior to habitual wake time) promotes phase advances… while exposure in the evening generally promotes phase delays.” (Yellow Book 2026). So 2–4 hours before your usual wake time is the low point; light after it pulls the clock earlier, evening light pushes it later.
Natural outdoor light is far stronger than indoor lighting. A 30-minute walk on arrival day speeds adaptation noticeably. When you need to avoid light, use sunglasses and blackout curtains.
Timeline — what to do when
| When | What to do |
| 3–4 days before | Eastward: shift sleep 30–60 min earlier daily. Westward: later |
| Night before | Don't stay up — sleep debt worsens jet lag |
| Boarding | Set your watch to destination time and think in it |
| In flight | Sleep if it's night there, stay awake if it's day. Hydrate; skip alcohol |
| Arrival day | Stay up until local bedtime; get outdoors |
| Days 2–3 | Keep wake-up time consistent — it matters more than bedtime |
Napping rules
- 20–30 minutes max — deeper sleep leaves you groggier
- Before 3pm — later naps wreck the night
- Always set an alarm
In-flight habits
| Water | Every 1–2 hours — cabins are very dry and dehydration amplifies fatigue |
| Alcohol | Avoid — it helps you fall asleep but degrades sleep quality |
| Caffeine | None after late afternoon destination time |
| Meals | Eating on destination schedule aids adjustment |
| Movement | Walk every 2–3 hours (circulation) |
| Sleep kit | Eye mask, earplugs — blocking light is key |
Helping recovery after arrival
- Fix your wake-up time — anchoring the morning shifts the clock faster than chasing bedtime.
- Eat breakfast — meal timing is another clock signal.
- Light exercise — a walk is enough; avoid intense workouts near bedtime.
- Melatonin — evidence supports timed use, but dose and timing matter and responses vary. Ask a professional first.
- Be careful with sleeping pills — they induce sleep without moving the body clock.
Short trips — consider not adjusting
For trips of two to three days, staying on home time can beat adapting. You'd barely adjust before returning — and you avoid a second round of jet lag at home. Just manage your energy around key meetings.
Questions that remain
How long does jet lag last?
By CDC figures, 1.5 hours a day westward and 1 hour a day eastward. An eight-hour shift is about 5.3 days west and 8 days east (our calculation). Good light timing shortens it further.
Can I sleep right after landing?
If it's night locally, yes. The problem is sleeping during local daytime — that stalls the shift.
Must I sleep on the plane?
Only when it's night at your destination. Sleeping regardless can slow adaptation.
Why is the return trip worse?
The return is often eastward, and travel fatigue has accumulated. Leave a spare day after getting home.
Beating jet lag isn't about endurance — it's about when you see light. A 30-minute walk on day one can save days.
Sources
- US CDC Travelers' Health — “Jet Lag” (checked July 2026). Source for “more than three time zones,” the west/east bedtime shift, “well-lit areas… during the day,” “naps, no more than 15-20 minutes,” “arrive… at least 2 days before any important events,” and following destination routines beyond a three-hour difference.
- US CDC Travelers' Health — “Pack Smart” (checked July 2026). Source for “mild sedative or sleep aid” appearing among the nine medicines. No ingredient or dose is given.
- US CDC Yellow Book 2026 — “Jet Lag Disorder” (checked August 2026). Source for 1.5 hrs/day west and 1 hr/day east, the 2–3 day pre-trip shift, melatonin 0.5–1 mg and the >5 mg caution, and the circadian nadir as the reference point for light.
- National Center for Mental Health, Korea — “Circadian rhythm sleep-wake disorders” (checked August 2026). The Korean agency source: adaptation time rises with the number of zones crossed, symptoms are more pronounced flying east, and advancing the body clock in the days before departure helps.
- Ministry of Food and Drug Safety approval disclosure — Circadin SR 2 mg (melatonin) (via the Korea Pharmaceutical Information Center, checked August 2026). Source for the prescription-only classification, the indication, and the dosing.
Where to check further
- Light timing for your specific trip. The CDC publishes no schedule and points to an individual calculator instead — the anchor is your own habitual wake time, not the clock. Before you fly, work out when 2–4 hours before your usual wake time actually falls.
- Whether to take melatonin. In Korea it is prescription-only and jet lag is not an approved indication. If you are considering it, talk to a doctor — that decision is beyond what this article can answer.
- Korea Disease Control and Prevention Agency health portal (health.kdca.go.kr). We could not open it this time to see whether it carries a jet lag entry. The Korean source here is the National Center for Mental Health instead.
As of August 2026. The numbers and directions come from CDC source text (the traveler page and Yellow Book 2026), and melatonin's Korean status from the MFDS approval document. The 1.5 hours in the chart is our rendering of “an hour or two,” and the 5.3-day / 8-day figures are the CDC adaptation rates divided by us. General information, not medical care. What to carry on board is in the packing guide; falling ill abroad is covered in emergencies overseas and drugstore part one.
