Altitude Sickness in Nepal: Prevention, Symptoms & Treatment

Altitude sickness kills trekkers in Nepal every year. It is the single most dangerous aspect of high-altitude trekking, and it can affect anyone — regardless of fitness, age or experience. I have seen ultra-runners get sick at 4,000 m and 60-year-olds cruise to 5,000 m without a problem. The honest truth is that altitude sickness is partly genetic, partly luck, and largely about acclimatization. This guide covers everything you need to know to stay safe.

What Is Altitude Sickness?

Altitude sickness (also called Acute Mountain Sickness or AMS) is the body's response to lower oxygen levels at high altitude. Above 2,500 m, the air pressure drops enough that each breath takes in less oxygen. The body compensates by breathing faster and deeper, but if you climb too quickly, the body cannot keep up. The result is fluid buildup in the lungs or brain, which can be fatal within hours if not treated.

There are three forms of altitude sickness:

1. AMS (Acute Mountain Sickness) — the mild form. Symptoms: headache, nausea, fatigue, loss of appetite, trouble sleeping. Affects most trekkers above 3,500 m to some degree. Treatable with rest and descent.
2. HAPE (High Altitude Pulmonary Edema) — fluid in the lungs. Symptoms: shortness of breath at rest, cough (initially dry, then pink/bloody), chest tightness. Fatal within hours if not treated.
3. HACE (High Altitude Cerebral Edema) — fluid in the brain. Symptoms: severe headache, confusion, loss of coordination, hallucinations, coma. Fatal within hours if not treated.

Both HAPE and HACE are medical emergencies requiring immediate descent and evacuation. The Wilderness Medical Society altitude sickness guidelines are the international clinical standard; the UK NHS altitude sickness page has plain-English advice for trekkers.

At What Altitude Does It Strike?

Altitude	Risk Level	Examples on Nepal Treks
Below 2,500 m	No risk	Kathmandu, Pokhara, trailheads
2,500–3,500 m	Mild risk	Poon Hill, Helambu, lower Annapurna
3,500–4,500 m	Moderate risk	Annapurna Base Camp, EBC trail up to Tengboche, Manaslu Circuit days 5–8
4,500–5,500 m	High risk	Everest Base Camp, Kala Patthar, Annapurna Circuit high camps, Manaslu Larkya La
Above 5,500 m	Very high risk	Three Passes trek, Dhaulagiri Circuit, Kanchenjunga BC, climbing peaks

Symptoms — How to Recognize Altitude Sickness

AMS Symptoms (Mild — Treatable)

• Headache (the most common symptom — usually worse at night)
• Nausea or vomiting
• Fatigue or weakness
• Dizziness or lightheadedness
• Loss of appetite
• Difficulty sleeping (frequent waking, gasping)
• Mild shortness of breath with exertion

HAPE Symptoms (Severe — Emergency)

• Shortness of breath at REST (not just when walking)
• Cough — initially dry, then producing pink/bloody sputum
• Chest tightness or congestion
• Blue lips or fingertips (cyanosis)
• Extreme fatigue, inability to walk

HACE Symptoms (Severe — Emergency)

• Severe headache that does not respond to painkillers
• Confusion, disorientation, or behavioural changes
• Loss of coordination (cannot walk a straight line, stumbling)
• Hallucinations
• Decreased consciousness, eventually coma

Prevention — The Golden Rules

1. Acclimatize slowly. Above 3,000 m, sleep no more than 500 m higher than the previous night. Take a rest day every 1,000 m of altitude gain.
2. Climb high, sleep low. During the day, you can climb higher than your sleeping altitude — this stimulates acclimatization. But always descend to sleep.
3. Stay hydrated. Drink 3–4 litres of water per day at altitude. Dehydration makes altitude sickness worse.
4. Avoid alcohol and sleeping pills. Both suppress breathing and make altitude sickness worse.
5. Eat well. At altitude, your appetite drops but your calorie needs increase. Eat even if you are not hungry — carbohydrates are particularly important.
6. Consider Diamox (acetazolamide). A prescription medication that helps the body acclimatize faster. 125 mg twice daily, starting 1 day before reaching altitude. Discuss with your doctor — see CDC's altitude sickness guidance.
7. Know the symptoms. If you have a headache plus any other symptom at altitude, assume it is AMS and do not climb higher until symptoms resolve.

The Lake Louise Score — Self-Assessment Tool

The Lake Louise Score is the standard self-assessment tool for AMS. Score yourself every morning at altitude:

Symptom	Score 0	Score 1	Score 2	Score 3
Headache	None	Mild	Moderate	Severe, debilitating
GI symptoms	None	Poor appetite or nausea	Moderate nausea or vomiting	Severe vomiting
Fatigue/weakness	None	Mild	Moderate	Severe, incapacitating
Dizziness	None	Mild	Moderate	Severe, off balance

Add up your score. If you score 3 or more (with a headache), you have AMS. Do not climb higher. Rest and hydrate. If symptoms worsen, descend.

Treatment — What to Do If You Get Sick

If You Have Mild AMS (Score 3–5)

1. Stop climbing. Take a rest day at your current altitude.
2. Hydrate — drink 1 litre of water immediately, then 3–4 litres over the day.
3. Take ibuprofen 400 mg for the headache.
4. Take Diamox 125 mg twice daily (if not already taking it).
5. Do not climb higher until you are symptom-free for 24 hours.

If You Have Severe AMS, HAPE or HACE

1. DESCEND IMMEDIATELY. Even 500 m of descent can be lifesaving.
2. Take Diamox 250 mg (for AMS/HACE).
3. Take Dexamethasone 8 mg initially, then 4 mg every 6 hours (for HACE). Prescription only.
4. Take Nifedipine 30 mg slow-release (for HAPE). Prescription only.
5. Use supplemental oxygen if available (most tea houses above 4,000 m have emergency oxygen).
6. Arrange helicopter evacuation if symptoms do not improve with descent.

Acclimatization Days — Why They Matter

Most Nepal trek itineraries include 1–2 acclimatization days. These are not rest days — they are active acclimatization days where you climb higher during the day and sleep at the same altitude. For example, on the Everest Base Camp trek, the standard acclimatization day at Namche Bazaar involves hiking up to the Everest View Hotel (3,880 m) for lunch, then returning to sleep at Namche (3,440 m). This 'climb high, sleep low' principle is the single most effective way to acclimatize.

See our how to acclimatize properly on EBC trek guide for the day-by-day acclimatization strategy on the EBC route.

Special Risks — Who Should Be Extra Careful

• People with heart or lung conditions — consult your doctor before trekking above 3,500 m
• Pregnant women — altitude is risky in pregnancy; do not trek above 3,500 m without medical clearance
• People who have had altitude sickness before — you are at higher risk of getting it again
• People who fly directly to high altitude — flying to Lukla (2,860 m) from Kathmandu (1,400 m) is a big jump; acclimatize carefully
• Fit people — fitness does NOT protect against altitude sickness. In fact, fit people are at higher risk because they climb too fast.

Altitude sickness is the most dangerous part of trekking in Nepal. Take it seriously. Acclimatize slowly, know the symptoms, carry Diamox, and do not be afraid to descend if you feel unwell. The mountains will be there next year — your life is more important than reaching Base Camp. For more, see our related guides on how to train for high altitude trekking and Nepal trekking insurance.