Most of Nepal's famous treks spend days above 3,000 m and several of them cross 5,000 m: Everest Base Camp sits at 5,364 m, Kala Patthar at about 5,545 m, and Thorong La on the Annapurna Circuit at 5,416 m. At those heights the air holds roughly half the oxygen it does at sea level. Your body can adapt — but only if you give it time.
This guide is general information, not medical advice. Talk to a doctor before a high-altitude trip, especially if you have heart, lung or blood pressure conditions.
What altitude sickness is
Acute Mountain Sickness (AMS) is your body's reaction to climbing faster than it can adapt. It can begin anywhere above about 2,500 m and it doesn't care how fit you are — marathon runners get it, grandparents sometimes don't. Fitness helps you walk; it doesn't help you acclimatise.
Common symptoms of mild AMS
- Headache (the most common sign)
- Loss of appetite or nausea
- Tiredness far beyond what the day's walking explains
- Dizziness or light-headedness
- Poor, broken sleep
Warning signs of severe altitude illness
- Breathlessness at rest, a persistent cough, gurgling breathing — possible fluid in the lungs (HAPE)
- Confusion, stumbling as if drunk, severe headache that painkillers don't touch, drowsiness — possible swelling of the brain (HACE)
Both HAPE and HACE are emergencies. The treatment is the same and it isn't optional: go down, immediately, with someone, even at night. Descending 500–1,000 m usually brings rapid improvement.
The acclimatisation rules that matter
- Above 3,000 m, aim to sleep no more than 300–500 m higher than the night before.
- Take a rest day roughly every 1,000 m of gain, or every three to four days — and walk higher on that day ("climb high, sleep low").
- Drink plenty of water, eat even when you don't feel like it, and skip alcohol and sleeping pills on the way up.
- Never go higher with symptoms. If they get worse while resting, go down.
- Build in a spare day or two. Itineraries that have no slack are the ones that go wrong.
Why the classic itineraries look the way they do
Everest Base Camp itineraries stop for an extra night in Namche Bazaar (3,440 m) and again in Dingboche (4,410 m) for exactly this reason. Annapurna Circuit trekkers take a day in Manang (3,540 m) before the push to Thorong La. If an operator offers a version that skips those days to save time, understand what you're trading away.
Flying straight to altitude removes the gradual gain a walk-in gives you. Lukla is at 2,860 m, and helicopter or flight arrivals to higher villages need even more caution. Trekking in the opposite direction — walking up from lower valleys — is slower but kinder to the body.
Medication
Acetazolamide (Diamox) is widely used in Nepal to speed up acclimatisation and is available in Kathmandu pharmacies. It has side effects and doesn't suit everyone, so discuss it with a doctor before your trip rather than at a tea house at 4,000 m. It is a tool, not a substitute for a sensible schedule.
How Trailma helps
The elevation profile is the most useful planning tool for altitude. Before you go, look at the sleeping altitudes for each stage of your route and check them against the 300–500 m rule. On the trail, your recorded activity shows exactly how much you climbed today — so when you feel rough, you can make an honest decision instead of a hopeful one.
Nobody has ever regretted an extra rest day at Namche. Plenty of people have regretted skipping one.
