Altitude sickness in Nepal — recognise it, prevent it, act on it
Acute mountain sickness is common above 3,000 m and usually harmless if you stop ascending. Its two progressions are not: confusion or loss of coordination signals HACE, and breathlessness at rest signals HAPE, and both require immediate descent. Standard guidance above about 2,750 m is to raise your sleeping elevation by no more than roughly 500 m a day, with a rest day every 1,000 m.
Altitude illness is the one risk on a Nepali trek that is both very likely to affect you in its mild form and capable of killing you in its severe form — and the gap between the two is a matter of hours and one bad decision.
It is also almost entirely preventable, because the cause is simple: ascending faster than your body can adapt. Fitness does not protect you. Youth does not protect you. Having been high before does not reliably protect you. Ascent rate does.
This guide follows mainstream travel-medicine guidance, principally the CDC Yellow Book chapter on high-altitude travel and altitude illness. It is not medical advice for your particular body — talk to a travel clinic before you go, especially about acetazolamide.
The three syndromes
Altitude illness is divided into three conditions. The first is common and usually benign; the other two are medical emergencies.
- Acute mountain sickness (AMS) — headache plus some combination of nausea, appetite loss, fatigue, dizziness and poor sleep, typically starting 6–12 hours after arriving at a new altitude. It feels remarkably like a hangover.
- High-altitude cerebral oedema (HACE) — swelling of the brain. The warning signs are mental status change (confusion, odd behaviour, drowsiness) and ataxia (loss of coordination, unable to walk a straight line). A life-threatening emergency.
- High-altitude pulmonary oedema (HAPE) — fluid in the lungs. The warning sign is breathlessness at rest, with a dry cough progressing to a wet one, and severe fatigue disproportionate to the effort. Also life-threatening, and it can occur without any AMS beforehand.
The prevention that works: ascent rate
Standard guidance is explicit. Once above about 9,000 ft (2,750 m), move your sleeping elevation no higher than roughly 1,600 ft (500 m) per day, and add an extra acclimatisation day for every 3,300 ft (1,000 m) gained.
Note that it is the sleeping elevation that counts, not the highest point you touch. This is why 'climb high, sleep low' works and why every good Nepali itinerary includes acclimatisation days at Namche (3,440 m) and Dingboche (4,410 m) on the Everest route, with a day-hike higher before returning to sleep.
It is also why the Everest Base Camp trek is scheduled at twelve to sixteen days rather than the six or seven the distance alone would suggest. Compressed itineraries sold as 'fast' Everest treks are selling you an increased chance of being evacuated.
- Above 2,750 m: gain no more than roughly 500 m of sleeping elevation per day.
- Add a rest day for every 1,000 m gained.
- Climb high during the day, sleep low at night.
- Never ascend with any AMS symptoms. Never sleep higher than the night before if you feel unwell.
- Drink enough that your urine stays pale; dehydration mimics and worsens AMS.
- Avoid alcohol and sleeping pills at altitude — both suppress breathing while you sleep.
The golden rules
Three rules, taught for decades by the Himalayan Rescue Association, cover almost every scenario:
- Any illness at altitude is altitude illness until proved otherwise.
- Never ascend with symptoms of AMS.
- If you are getting worse, or you have signs of HACE or HAPE, descend immediately — do not wait for morning.
When to descend, and how far
Descent is the definitive treatment for every form of altitude illness, and it works fast. Mild AMS often resolves with a rest day at the same altitude; anything more needs to go down.
For HACE or HAPE, descend immediately and by whatever means available — walking, animal, porter carry, or helicopter. Even 300 to 1,000 m of descent can produce dramatic improvement. Do not let darkness be the reason to wait; people die overnight at altitude waiting for daylight.
A person with suspected HACE must never descend alone, because confusion and ataxia make a night descent dangerous. Someone stays with them.
Medication: what it does and does not do
Talk to a travel clinic before your trip; the notes below are context, not a prescription.
Acetazolamide (Diamox) speeds acclimatisation and is used for prevention when a rapid ascent is unavoidable, and as an aid in treating AMS. It does not mask symptoms and it is not a licence to ascend faster. It has real side effects — increased urination and tingling in the fingers and toes are common — and it is a sulfonamide, so it matters if you have that allergy.
Dexamethasone treats AMS and HACE but does not aid acclimatisation; it buys time to descend. Nifedipine is used for HAPE. Both are emergency drugs to be carried and used under guidance, not routine trekking supplies.
Portable hyperbaric bags (Gamow bags) and supplementary oxygen exist at some lodges and aid posts and are a bridge to descent, not a substitute for it.
Where to get help on the trail
The Himalayan Rescue Association runs seasonal aid posts staffed by volunteer doctors at Pheriche (Everest region) and Manang (Annapurna Circuit), plus a clinic in Kathmandu. If you are anywhere near either, that is where you go, and their free daily altitude talks are genuinely worth attending.
Elsewhere, health posts exist in larger villages, and your guide is your first line — a licensed guide is trained in altitude recognition, which is a substantial part of the argument for the guide requirement.
For evacuation, your insurer's 24-hour line coordinates a helicopter. Keep that number written down somewhere that does not depend on a phone battery, along with your policy number and passport details.
The particular Nepali risk: flying straight to altitude
Two Nepali itineraries create altitude problems that walking does not. Flying Kathmandu (1,400 m) to Lukla (2,860 m) gains 1,400 m in forty minutes, which is why the first day walks downhill to Phakding (2,610 m) rather than up.
The sharper risk is the helicopter or short flight into higher airstrips, and the increasingly-sold 'Everest Base Camp helicopter tour' with a landing at Kala Patthar (5,545 m). Going from Kathmandu to over 5,000 m within an hour gives your body no adaptation at all, and people do become seriously unwell on these tours.
The same applies to driving to Muktinath (3,760 m) from Pokhara in a day, now that the road exists. Fast access does not change your physiology.
Key takeaways
- ✓Above about 2,750 m, gain no more than roughly 500 m of sleeping elevation per day and rest a day per 1,000 m.
- ✓AMS is a headache plus hangover-like symptoms; it means stop ascending, not push on.
- ✓Confusion or loss of coordination means HACE. Breathlessness at rest means HAPE. Both mean descend immediately, at night if necessary.
- ✓Descent is the definitive treatment — 300–1,000 m can produce dramatic improvement. Never send a confused person down alone.
- ✓Fast access — Lukla flights, helicopter tours to Kala Patthar, driving to Muktinath — creates altitude risk that walking does not.
Altitude Sickness in Nepal — FAQ
At what altitude does altitude sickness start in Nepal?+
Acute mountain sickness becomes common above about 2,500–3,000 m, which on Nepali treks means from around Namche Bazaar (3,440 m) on the Everest route or Manang (3,519 m) on the Annapurna Circuit. Individual susceptibility varies enormously and is not predicted by fitness.
How fast should you ascend to avoid altitude sickness?+
Once above about 2,750 m, standard guidance is to raise your sleeping elevation by no more than roughly 500 m per day, with an additional acclimatisation day for every 1,000 m gained. The sleeping elevation is what counts, not the highest point you touch during the day.
What are the danger signs of altitude sickness?+
Two in particular. Mental status change or loss of coordination — confusion, odd behaviour, inability to walk a straight line — signals high-altitude cerebral oedema. Breathlessness at rest signals high-altitude pulmonary oedema. Both are life-threatening and require immediate descent.
Does Diamox prevent altitude sickness?+
Acetazolamide (Diamox) speeds acclimatisation and is used when a rapid ascent is unavoidable, and it aids treatment of AMS. It is not a licence to ascend faster, it does not mask symptoms, and it has real side effects. Discuss it with a travel clinic before your trip, particularly if you have a sulfa allergy.
What should I do if I get altitude sickness on a trek?+
Stop ascending. Rest at the same altitude and see whether mild symptoms resolve. If they worsen, or if there is any confusion, loss of coordination or breathlessness at rest, descend immediately — even at night — and get to a clinic or an HRA aid post. Never ascend while you have symptoms.
Where are the altitude clinics in Nepal?+
The Himalayan Rescue Association runs seasonal aid posts staffed by volunteer doctors at Pheriche in the Everest region and Manang on the Annapurna Circuit, plus a Kathmandu clinic. Both aid posts run free daily altitude talks that are well worth attending.
Related guides
Sources & data note
Clinical guidance in this guide follows the CDC Yellow Book chapter on high-altitude travel and altitude illness and Wilderness Medical Society practice guidelines. It is general information, not medical advice for an individual; drug choices and doses must come from a clinician who knows your history. The Nepal-specific observations about helicopter tours and road access to Muktinath are our own analysis of how fast access changes exposure, not a published finding. Guides are written from primary sources — Nepali government departments, operators, park authorities and standards bodies — and each guide lists the sources used for its own facts. Rules, fees and prices in Nepal change; treat figures as current at the review date shown on each guide and verify anything money- or visa-critical with the issuing authority before you rely on it.
- High-Altitude Travel and Altitude Illness — CDC Yellow BookUS Centers for Disease Control and Prevention ↗
- Himalayan Rescue Association Nepal — altitude aid posts and adviceHimalayan Rescue Association ↗
- Wilderness Medical Society clinical practice guidelines for acute altitude illnessWilderness & Environmental Medicine ↗
- Nepal Tourism Board — official site (trekking and trekker information)Nepal Tourism Board ↗