Altitude Sickness on Nepal Treks: Symptoms, Prevention and What to Do

Altitude Sickness on Nepal Treks: Key Facts

Last updated: March 2026 | Reading time: 9 min

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Altitude sickness is the most common reason trekkers do not complete their route in Nepal. It is also the most misunderstood. It is not about fitness — it affects experienced mountaineers and first-timers equally. It is not predictable — you cannot know in advance how your body will respond. And it is not something to push through.

This guide covers what altitude sickness actually is, how to recognise it early, what prevents it, and exactly what happens on a MountainKick trek when a trekker starts showing symptoms.

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What Is Altitude Sickness?

Altitude sickness, medically called Acute Mountain Sickness (AMS), occurs when your body does not have enough time to adjust to reduced oxygen levels at elevation. As you gain altitude, air pressure drops and each breath delivers less oxygen. Your body compensates by breathing faster and producing more red blood cells, but this adaptation takes time. Push too high too fast and the system is overwhelmed.

AMS typically begins above 2,500m, though some people feel effects as low as 2,000m. On Nepal’s main trekking routes you are well into AMS territory by day three or four of most itineraries. This is exactly why acclimatisation days are built in, not added as optional padding.

There are three severity levels: mild AMS, which is common and manageable; HACE (High Altitude Cerebral Edema), where fluid builds up around the brain; and HAPE (High Altitude Pulmonary Edema), where fluid builds up in the lungs. HACE and HAPE are medical emergencies requiring immediate descent and evacuation. Both can develop rapidly from unrecognised mild AMS.

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Symptoms: How to Recognise Each Stage

Mild AMS

The early signs are easy to dismiss as tiredness from a long day of trekking. That is why they are dangerous. Mild AMS symptoms include persistent headache (the most reliable early indicator), nausea or loss of appetite, fatigue beyond what the day’s exertion warrants, dizziness or light-headedness, and disturbed sleep.

Mild symptoms at a new altitude are normal and often resolve with rest, hydration, and time. The rule: if symptoms are mild and not worsening after 24 hours of rest at the same altitude, you may be acclimatising. If they are worsening, descend.

Moderate AMS

Moderate AMS means the body is struggling and rest alone will not fix it. Signs include severe or persistent headache unrelieved by painkillers, vomiting rather than nausea, marked weakness, and significant shortness of breath even at rest. At this stage, descent is necessary.

Severe AMS / HACE / HAPE

These are emergencies. Watch for loss of coordination (ataxia) — test by walking a straight line heel-to-toe. Also watch for confusion, disorientation, or irrational behaviour; a persistent dry cough developing into a wet gurgling cough; and breathlessness so severe the person cannot walk or speak normally. If any of these appear, the response is immediate descent and emergency evacuation. There is no waiting.

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Prevention: The Three Things That Actually Work

1. A properly paced itinerary

The most effective prevention is time. The standard guideline above 3,000m is to ascend no more than 300 to 500m per day in sleeping altitude, with a rest day every 3 to 4 days. This is why a well-structured EBC itinerary takes 14 days rather than 10. Those extra days are not padding — they are the reason most trekkers complete the route.

Be wary of operators offering unusually short itineraries. A 10-day EBC package skips acclimatisation days that exist for a reason. The extra cost of a 14-day trek is insignificant compared to an emergency evacuation, or simply not reaching Base Camp.

2. Hydration

Dehydration worsens AMS symptoms significantly and is easy to let happen at altitude. You are breathing harder, the air is dry, and you may not feel thirsty. Aim for 3 to 4 litres of water per day on the trail. Urine colour is the best indicator: pale yellow means you are hydrated, dark yellow means drink more immediately.

Avoid alcohol above 3,000m, especially in the first few days at a new altitude. It dehydrates, impairs sleep quality, and masks early AMS symptoms.

3. Pace yourself on the trail

Move slowly. At altitude, the trekker who overtakes everyone on the way up is often the one being evacuated three days later. A sustainable pace — slow enough to hold a conversation without breathing heavily — protects your acclimatisation more than any supplement.

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Diamox: Should You Take It?

Diamox (Acetazolamide) is a prescription medication that speeds up acclimatisation by stimulating faster breathing, which increases blood oxygen levels. It is genuinely effective and widely used by trekkers on high-altitude routes in Nepal.

MountainKick leaves the decision about Diamox entirely to trekkers and their doctors. Dosage, timing, and suitability depend on individual health history, other medications, and whether you have sulfa allergies (Diamox is a sulfa drug). Speak to your GP or a travel medicine clinic before you leave home. A prescription is easy to get in most countries and having it available on the trail even if you do not use it is sensible.

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What Happens on the Trail If You Get Sick

Every MountainKick guide carries a pulse oximeter as standard equipment on all treks. A pulse oximeter measures blood oxygen saturation (SpO2), the single most reliable on-the-ground indicator of how well your body is acclimatising. Guides check SpO2 readings regularly, not just when a trekker reports feeling unwell. This early monitoring catches problems before they escalate.

The MountainKick response when AMS symptoms appear:

• Stop ascending immediately. No further altitude gain until symptoms resolve or the decision to descend is made.
• Rest, hydrate, monitor. For mild symptoms at a new altitude, rest with continuous monitoring.
• If symptoms worsen or do not improve, descend. Even 300 to 500m of descent brings significant relief in most cases. Descending at night is preferable to waiting until morning if symptoms are worsening.
• Horses and mules for assisted descent. On routes where pack animals are available, guides arrange horse or mule transport for trekkers who cannot walk down safely.
• Helicopter evacuation for severe cases. If symptoms indicate HACE or HAPE, evacuation is arranged immediately. Evacuation from most points on Nepal’s main routes can be arranged within 1 to 3 hours in daylight.

Your travel insurance details are collected before the trek begins. In a helicopter evacuation, the operator needs insurance confirmation to dispatch. This is why valid high-altitude rescue insurance is non-negotiable. For guidance on what your policy must cover, read our Nepal trekking insurance guide.

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Helicopter Evacuation in Nepal: What to Expect

Nepal has a well-established helicopter rescue infrastructure. Evacuation typically flies the trekker to Kathmandu or the nearest hospital with appropriate facilities. From most EBC-route locations, that means Kathmandu. From the Annapurna region, it may mean Pokhara.

Cost without insurance: USD 3,000 to 6,000 depending on pickup location and distance. With valid insurance covering helicopter evacuation, it is covered in full, arranged directly between your guide and the insurance company’s emergency line. This is why you give your guide your insurance details before day one, not as an afterthought.

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Which Nepal Treks Carry the Highest AMS Risk?

AMS Risk by Trek — Nepal 2026

Trek	Max sleeping altitude	AMS risk	Acclimatisation days
Everest Base Camp	5,364m (Gorak Shep)	High	2 (Namche + Dingboche)
Annapurna Circuit	4,800m (High Camp)	Moderate to High	1 to 2 (Manang)
Annapurna Base Camp	4,130m (ABC)	Moderate	Built into ascent pace
Manaslu Circuit	5,106m (Larkya La)	High	1 to 2 (Samdo)
Poon Hill	3,210m (Poon Hill)	Low	None needed

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Frequently Asked Questions

Can fit people get altitude sickness?

Yes, and they often do. Cardiovascular fitness does not protect against AMS. Very fit trekkers sometimes move faster than they should and ascend too quickly, increasing their risk. The mountains do not care about your VO2 max.

What if I have had altitude sickness before?

Previous AMS is a risk factor for future episodes. Tell your guide before the trek begins. Your itinerary may be adjusted to include extra acclimatisation time, and your guide will monitor you more closely at altitude transitions.

Can I trek to EBC if I live at sea level?

Yes. The majority of EBC trekkers come from sea-level countries and complete the trek successfully. A properly structured 14-day itinerary with acclimatisation days gives your body the time it needs. Short-cutting the itinerary to save a day or two is where things go wrong.

Should I go to altitude before my trek to acclimatise?

Spending a few days in Kathmandu (1,400m) before your trek does not provide meaningful acclimatisation for EBC. The difference between 1,400m and 5,000m is too large. What it does do is help with jet lag and gives you time to sort gear and logistics. Acclimatisation happens on the trail through the paced itinerary.

What is the difference between AMS, HACE, and HAPE?

AMS (Acute Mountain Sickness) is the common form — headache, nausea, fatigue. Manageable with rest and monitored descent if worsening. HACE is fluid building around the brain — causes confusion and loss of coordination, requires immediate descent and evacuation. HAPE is fluid in the lungs — causes severe breathlessness and a wet cough, also requires immediate evacuation. Both HACE and HAPE can develop rapidly from unrecognised mild AMS.

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Further Reading

• Travel Insurance for Nepal: What Your Policy Must Cover
• Everest Base Camp Trek Cost 2026: The Complete Breakdown
• Annapurna Base Camp Trek Cost 2026: The Complete Breakdown
• Nepal Trekking Permits 2026: Costs, Rules and What’s Changed
• Lukla Flight via Ramechhap 2026: The Complete Guide
• Solo Female Trekking Nepal: Safety, Guides and What to Expect