Jet lag isn’t just “feeling tired after a flight.” It’s a genuine circadian rhythm disorder caused by rapid travel across time zones, and it affects virtually every system in your body — digestion, cognition, mood, immune function, and of course, sleep. The good news is that we actually understand the physiology well enough to manage it effectively. The bad news is that most advice you’ll find online is vague, oversimplified, or just wrong.

Here’s what actually works, based on circadian biology.

Understanding the Core Problem

Your internal clock — the suprachiasmatic nucleus (SCN) in your hypothalamus — runs on a roughly 24.2-hour cycle and synchronises primarily through light exposure to your retinas. When you fly from Sydney to London, your SCN is still operating on Australian Eastern time. Every cell in your body is running on the wrong schedule.

The general rule: your circadian clock can shift about 1-1.5 hours per day when properly managed. That means a 10-hour time zone change takes roughly 7-10 days to fully adjust to without intervention. With strategic management, you can cut that roughly in half.

Light Exposure: The Most Powerful Tool

Light is the single strongest zeitgeber (time cue) for your circadian system. Getting light exposure right matters more than any supplement or medication.

The principle is simple but the timing is everything:

• Travelling east (advancing your clock): Seek bright light in the morning at your destination. Avoid light in the evening before your trip and the first few days after arrival.
• Travelling west (delaying your clock): Seek bright light in the evening at your destination. Avoid early morning light for the first few days.

The critical detail most guides skip: there’s a “dead zone” around your core body temperature minimum (typically 4-5 AM in your home time zone). Light exposure before this minimum delays your clock. Light exposure after this minimum advances your clock. Get it backwards and you’ll make your jet lag worse.

The CDC’s travel health guidelines recommend calculating your temperature minimum and planning light exposure around it. For eastward travel, this matters enormously.

Melatonin: Useful but Misunderstood

Melatonin doesn’t knock you out — at least, that’s not its primary circadian function. At physiological doses (0.5-1 mg), it acts as a “darkness signal” to your SCN, telling your clock that night has arrived. Higher doses (3-5 mg) do have a mild sedative effect, but that’s separate from the circadian shifting action.

For jet lag management, timing matters far more than dose:

• Eastward travel: Take 0.5-1 mg of melatonin in the early evening (destination time) for several days before and after your trip. This advances your clock.
• Westward travel: Melatonin is less useful for delaying your clock. If you wake too early at your destination, a small dose (0.5 mg) upon waking in the middle of the night can help you fall back asleep, but it won’t dramatically shift your rhythm.

Don’t take melatonin during the day at your destination. It can worsen grogginess and send confusing signals to your circadian system.

Pre-Trip Circadian Shifting

This is the strategy that makes the biggest difference and the one most travellers skip because it requires planning.

Starting 3-4 days before an eastward trip, gradually shift your sleep schedule earlier by 30-60 minutes per day. Combine this with morning bright light exposure (a 10,000 lux light box works well) and evening light avoidance. By departure day, you’ve already shifted 2-3 hours toward your destination time.

For westward trips, do the reverse — stay up later, seek evening light, sleep in slightly later each morning.

The Sleep Foundation’s jet lag calculator can help you map out a shifting schedule based on your specific travel dates and time zones.

In-Flight Strategies

Immediately switch to destination time. Change your watch, eat meals on the new schedule, and try to sleep (or stay awake) according to what time it is where you’re going.

Stay hydrated. Cabin humidity runs around 10-20%, and dehydration worsens fatigue and cognitive fog. Alcohol makes everything worse — it fragments sleep architecture and promotes dehydration.

Move around. Beyond DVT prevention, physical movement helps signal wakefulness to your body when you’re trying to stay alert on the new schedule.

Consider strategic caffeine. Coffee can help maintain alertness during destination daytime, but cut it off at least 6 hours before your planned sleep time at destination. Caffeine’s half-life is 5-6 hours, and it directly blocks adenosine receptors that promote sleep.

The Honest Bottom Line

Jet lag is a temporary condition, and your body will eventually adjust on its own. But “eventually” can mean a week of impaired performance, disrupted digestion, and terrible sleep. If you’re travelling for a wedding, an important meeting, or a once-in-a-lifetime vacation, that week of misery costs you something real.

The strategies above aren’t complicated, but they do require planning and discipline. Start adjusting before you leave, use light exposure strategically, keep melatonin doses low and well-timed, and resist the temptation to just “push through” on willpower alone. Your circadian clock doesn’t respond to willpower. It responds to photons and consistency.