Altitude sickness on Nepal treks

From CDC's Yellow Book 2026. AMS affects about a quarter of people who sleep above 2,450 m, and on the Everest trail CDC puts it near 30% even on standard schedules.

Doctors score four symptoms from 0 to 3. Three points or more, with at least one from headache, after a recent climb, is AMS (Lake Louise consensus, 2018). The 2018 version dropped sleep as a symptom.

• CDC: once above 3,000 m, raise the height you sleep at by no more than 500 m a night, and add an extra night for every 1,000 m gained. Do not go from below 1,200 m to sleep above 2,750 m in one day.
• Wilderness Medical Society (2019): the same 500 m a day above 3,000 m, with a rest day, sleeping at the same height, every three or four days.
• Nepal Tourism Board: no more than 300 to 500 m a day above 2,500 m, and a rest day after every 1,000 m.
• Climb high, sleep low is allowed: the rule counts where you sleep, not how high you walk that day.
• Alcohol: none for the first 48 hours at a new height (CDC).

From each trek's day-by-day plan at the usual pace. A night that "breaks the rule" sleeps more than 500 m higher than the night before, above 3,000 m; 8 of the ten plans have at least one. Each trek page marks them on the day they fall.

These are the doses CDC's Yellow Book 2026 gives doctors. They are not advice to take anything: ask a doctor before you go, and tell them about any allergy and any other medicine. No pill replaces going down.

• Acetazolamide (Diamox), to prevent AMS: "125 mg every 12 hours, beginning the day before ascent and continuing the first two days at altitude, and longer if ascent continues"; 250 mg twice a day for people over 100 kg. The Wilderness Medical Society's 2024 update gives the same 125 mg every 12 hours. Tingling in the fingers is the common side effect.
• Acetazolamide, to treat AMS: 250 mg twice a day.
• Dexamethasone: for treatment, 4 mg every 6 hours for AMS; for HACE, 8 mg once and then 4 mg every 6 hours.
• Nifedipine, for HAPE: 30 mg of the slow-release form every 12 hours, or 20 mg every 8 hours.
• Ibuprofen eases the headache but does not treat the illness.
• Garlic soup is served on every trail; no medical guideline says it prevents anything.
• Children: CDC's own chapter gives two different children's doses, so none is quoted here. Ask a doctor.

1. 1Stop climbing. Never go up to sleep higher with any symptom.
2. 2If it is a mild headache only, rest at the same height. Better by morning, carry on slowly.
3. 3Worse, or no better after a rest day: go down, 300 to 1,000 m or until the symptoms go.
4. 4Confusion, stumbling, or breathless at rest: go down now, even at night, with someone who can walk with them. Oxygen, where a lodge or rescue post has it, helps on the way.
5. 5Helicopters fly mostly in the morning, when the wind is lighter. CDC puts a rescue at about USD 4,000 an hour, USD 8,000–10,000 in all; insurance that covers it is worth having.

• Pheriche (4,371 m, Everest trail): the Himalayan Rescue Association's first aid post, since 1973, staffed by volunteer doctors in the spring and autumn seasons, with a talk on altitude sickness most days.
• Manang (Annapurna Circuit): since 1981; treats about a thousand patients a year, most of them Nepali, free or almost free for Nepalis.
• Everest Base Camp: the association's clinic for climbers and staff, from about 1 April to the end of May.
• Gosaikunda (4,380 m): a temporary camp at Janai Purnima, when thousands of pilgrims climb to the lake. Thorong Phedi's clinic is closed.
• In spring 2025 the posts treated 1,823 people. 1,380 of them were Nepali.

From mid-July 2025 to mid-July 2026, the Annapurna Conservation Area Project counted 25 deaths from altitude sickness in its region: 15 in Mustang, 8 in Manang, one at Annapurna Base Camp and one on Mardi Himal. Twelve were Nepali, four of them guides and porters, and nine were Indian (Republica, 23 July 2026).

At Gosaikunda in August 2025, about 10,000 pilgrims climbed to the lake for Janai Purnima and 20 were sent to hospital with fluid on the lungs or the brain (Kantipur). The pattern in both places is the same: a fast climb, often by road, to sleep high on the first night.

Altitude sickness is लेक लाग्नु in Nepali, and the newspapers write लेक लागेर ("from the altitude") and लेक लाग्ने समस्या. The whole guide is also in Nepali: लेक लाग्नु: लक्षण, उपचार र बच्ने उपाय.