Altitude Sickness in Nepal: Symptoms, Prevention & Treatment (2026)

What Is Altitude Sickness?

Altitude sickness — or acute mountain sickness (AMS) — is the body's response to reduced oxygen availability at high elevations. At sea level, the air contains approximately 21% oxygen regardless of altitude. The problem is barometric pressure: at 3,600 metres, the atmospheric pressure is roughly 60% of sea level, meaning each breath delivers significantly fewer oxygen molecules to the lungs. The body can adapt — slowly — by increasing breathing rate, producing more red blood cells (a process that takes weeks), and shifting blood chemistry. But when the ascent outpaces the body's adaptive capacity, the physiological mismatch produces altitude illness.

Altitude illness exists on a spectrum of increasing severity. AMS (mild) is uncomfortable and slows trekkers down for a day or two. HACE (High-Altitude Cerebral Edema — fluid on the brain) and HAPE (High-Altitude Pulmonary Edema — fluid in the lungs) are life-threatening medical emergencies that kill otherwise healthy trekkers every year in Nepal. The progression from mild symptoms to fatal illness can happen in as little as 6–12 hours — which is why every trekker above 3,000 metres must know the warning signs and be willing to descend early.

Who Gets Altitude Sickness?

Altitude sickness has no respect for age, gender, or fitness level. Fit young men in their 20s are among the most common AMS patients — because they ascend too fast, overconfident in their physical condition. The following factors increase risk:

• Rapid ascent — flying directly to Lukla (2,860m) from Kathmandu (1,400m) in 30 minutes is the single biggest risk factor on the Everest Base Camp trek. There is no gradual road transit to allow adaptation
• Previous history of altitude sickness — if you have had AMS before, you are significantly more likely to develop it again. This does not mean you cannot trek at altitude, but you must be more cautious
• Exertion on arrival — arriving at a high-altitude teahouse and immediately hiking to a viewpoint or summit push is counterproductive. The first 24–48 hours at altitude should be minimal-effort: rest, hydrate, and let the body adjust
• Dehydration and alcohol — altitude increases fluid loss through respiration (dry mountain air) and urination. Alcohol suppresses breathing during sleep, reducing oxygen uptake. Avoid alcohol for the first 3–4 days above 3,000m
• Sleeping altitude increase >300m per night — the "climb high, sleep low" rule exists because the body does its most significant adaptation during sleep, when oxygen saturation naturally drops. Raising sleeping altitude too quickly prevents this adaptation

Prevention Strategies That Work

The Ascent Guidelines

The Wilderness Medical Society (WMS) and the International Society of Mountain Medicine (ISMM) publish evidence-based guidelines for altitude ascent that all Nepal trekkers should follow. These are not suggestions — they are built from decades of altitude illness data:

• Above 3,000m, do not increase sleeping altitude by more than 500m per day — the standard "500m rule." Some sources use 300m for conservative safety. For most trekkers, 400–500m is a manageable target
• Take an acclimatisation day every 3–4 days or every 1,000m gained — a full day at the same altitude (or slightly lower) with gentle walks to higher points during the day, returning to sleep at the lower altitude. Namche Bazaar (3,440m) and Dingboche (4,410m) are the standard acclimatisation stops on the EBC trek
• The "climb high, sleep low" principle — hike to a higher elevation during the day (e.g., the Everest View Hotel at 3,880m from Namche Bazaar), then return to sleep at the lower elevation (3,440m). This exposes the body to higher altitude without committing to sleeping there
• Avoid direct flight to Lukla followed by rapid ascent — consider spending a night at Phakding (2,610m) before pushing to Namche Bazaar (3,440m). This small adjustment gives the body an extra 24 hours of adaptation

Hydration & Nutrition

Dehydration exacerbates altitude symptoms because it thickens the blood, increasing cardiac load at a time when the body is already stressed. The standard recommendation: 3–4 litres of fluid per day above 3,000m. Dal bhat (the Nepali lentil and rice meal) is genuinely excellent trekking food — high in carbohydrates, protein, and easily digestible. Carbohydrates require less oxygen to metabolise than fats, making them the preferred energy source at altitude. Most teahouses serve dal bhat with unlimited refills for 500–800 NPR (~$4–$6), making it both the most nutritious and most economical option on the trail.

Diamox (Acetazolamide) — Medication Guide

Acetazolamide (brand name Diamox) is the only medication proven to prevent and treat AMS. It works by inhibiting the enzyme carbonic anhydrase, which creates a metabolic acidosis that stimulates the respiratory centre to increase breathing rate and depth — effectively tricking the body into adapting faster. It reduces AMS incidence by approximately 50% when taken prophylactically. It is not a substitute for proper acclimatisation, nor does it provide immunity from HACE or HAPE.

Dosage Protocol

Side Effects

Diamox is generally well-tolerated, but it has side effects. The most universal: tingling in the fingers, toes, and lips (paraesthesia), which affects nearly all users and is harmless. It can also cause altered taste perception (carbonated drinks taste flat). Less common: nausea, drowsiness, and frequent urination. Diamox is a sulphonamide and should not be taken by anyone with a sulphonamide allergy (though the cross-reactivity risk is debated — consult a doctor). It also reduces the effectiveness of lithium and can interact with certain blood pressure medications.

Alternative Medications

Dexamethasone (Decadron) — a corticosteroid sometimes used to treat HACE. It reduces brain swelling but does not treat the underlying altitude exposure and should only be used under medical guidance. Nifedipine — used to prevent and treat HAPE in susceptible individuals. Not for routine prophylaxis; reserved for people with a known history of HAPE. Ibuprofen — some studies suggest it modestly reduces the incidence of AMS headache but does not prevent HACE or HAPE. It is useful for symptom management but not a substitute for Diamox.

Treatment & Emergency Response

The treatment protocol for altitude sickness depends entirely on severity. The following decision framework is adapted from the Himalayan Rescue Association's guidelines used in their Everest Base Camp and Manang clinics.

Mild AMS (Headache + Nausea)

Stop ascending. Rest at the same altitude. Hydrate. Take paracetamol or ibuprofen for headache. Do not ascend until symptoms resolve completely. If no improvement within 24 hours, descend 300–500 metres. Most mild AMS resolves within 24–48 hours with rest at the same altitude. About 20% of trekkers experience mild AMS on the EBC trek; the vast majority continue after a rest day.

Moderate-Severe AMS (Vomiting, Severe Headache, Dizziness)

Descend immediately. Do not wait for morning. A descent of 500–1,000 metres is the standard response. Oxygen (2–4 L/min by mask) provides temporary relief but is not a substitute for descent. Diamox 250 mg twice daily can be started. The Gamow bag (portable hyperbaric chamber) can simulate a descent of 1,500–2,500 metres by increasing the pressure inside the bag — this buys critical time for rescue but must be followed by actual descent.

HACE / HAPE (Confusion, Stumbling, Breathing at Rest, Pink Sputum)

Immediate descent. This is an emergency. Do not wait for helicopter rescue to arrive — start descending on foot while calling for evacuation. For HACE: administer Dexamethasone (8 mg first dose, then 4 mg every 6 hours) if available. For HAPE: Nifedipine (30 mg slow-release every 12 hours) if available. Place the patient in a sitting position (not lying flat) for HAPE to reduce pulmonary pressure. Keep the patient warm and calm. Coordinate helicopter evacuation via your trekking company's emergency number or through the nearest teahouse (most have satellite phones and can contact rescue coordinators).

EBC Acclimatisation Schedule

The following schedule represents the safest standard itinerary for the Everest Base Camp trek, incorporating mandatory acclimatisation days at the established points. This schedule adds 1–2 days compared to "express" itineraries (12 vs. 10 days walking) but significantly reduces the risk of altitude illness.