Altitude Sickness on Treks: How to Prevent and Handle It

Altitude sickness is the single most common reason treks fail — and it respects neither fitness nor experience. Above roughly 2,500 m, the thinner air affects everyone: most trekkers first notice it as a headache, poor sleep and lost appetite, and most cases stay mild and resolve with rest. But a small share progress to life-threatening high-altitude cerebral or pulmonary edema (HACE and HAPE), where descent — not willpower — is the treatment.

This guide covers the widely agreed acclimatization rules, how to recognise the three altitude illnesses, medication basics and the decision points that keep you safe — consolidated from published medical guidance and trekker reports. It is general information, not medical advice: talk to your doctor before any high-altitude trip, especially if you have heart, lung or blood-pressure conditions.

The golden rules of acclimatization

Acclimatization is the only reliable prevention, and it follows a few simple rules repeated in every serious altitude guideline. Above 2,500 m, do not increase your sleeping altitude by more than 300–500 m per day; take a rest day for every 1,000 m of gain; and follow ‘climb high, sleep low’ — day hikes can go higher than your camp. Never fly or drive straight above 3,500 m without planning rest days first.

Drink plenty of fluids (3–4 litres a day is the commonly quoted target), eat carbohydrate-rich food, avoid alcohol — especially in the first 48 hours — and go easy on day one. Most importantly: never ascend while you have symptoms. If you feel ill, stay put until you are fully better; if symptoms worsen at the same altitude, descend. The summit is optional; getting down is mandatory.

Recognising AMS, HACE and HAPE

Acute mountain sickness (AMS) is the mild and common form: headache plus some combination of nausea, fatigue, dizziness, poor sleep and loss of appetite. Mild AMS at a rest altitude usually settles in 24–48 hours; if it does not, or it worsens, the answer is descent of at least 500–1,000 m.

HACE and HAPE are emergencies. Warning signs include breathlessness at rest, a persistent cough (possibly with pink or rusty sputum), confusion, loss of coordination — the classic field test is being unable to walk heel-to-toe in a straight line — severe headache with vomiting, or extreme fatigue. These can develop even without prior AMS. The response is immediate descent, ideally with oxygen if available, and they are the reason insurance with high-altitude helicopter evacuation is non-negotiable on serious routes.

Diamox and other medications

Acetazolamide (Diamox) is the most studied altitude medication: it speeds up acclimatization by deepening breathing. The commonly published preventive dose is 125 mg twice daily, started 24 hours before ascending above 2,500 m and continued a couple of days at maximum altitude; treatment of established AMS is usually quoted at 250 mg twice daily alongside rest. Typical side effects include tingling in fingers and toes, more frequent urination and a flat taste to fizzy drinks — harmless but noticeable.

Diamox is a sulfa drug and can trigger allergic reactions; discuss it with your doctor well before the trip and consider a trial dose at home. It aids acclimatization — it is not a cure, and it never justifies ascending with symptoms or skipping descent when HACE or HAPE are suspected. Painkillers can treat the headache of mild AMS, but masking symptoms while continuing up is exactly how mild AMS becomes dangerous.

Planning a high-altitude trek

Build the acclimatization rules into the itinerary, not around it: choose routes with built-in rest days (the standard Everest Base Camp itinerary’s rest days at Namche Bazaar and Dingboche exist for this reason), and pick a trip length that allows them rather than a schedule that forces pace.

Trek with a partner or group — impaired judgment is itself a symptom, and solo decisions at altitude are unreliable. Learn the symptoms before you go, brief everyone in the group on the ‘never ascend with symptoms’ rule, carry the medications your doctor prescribed, and confirm your insurance explicitly covers trekking to your trip’s maximum altitude and helicopter evacuation from it. Fitness helps you enjoy the trek, but only acclimatization protects you from altitude — the fittest trekker in the group is just as vulnerable.