Altitude Sickness on Nepal Treks: Symptoms, Prevention and What to Do
Last updated: March 2026 | Reading time: 9 min
Altitude sickness is the most common reason trekkers don’t complete their route in Nepal. It’s also the most misunderstood. It’s not about fitness. It affects experienced mountaineers and first-timers equally. It’s not predictable. You can’t know in advance how your body will respond. And it’s 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.
In this guide:
- What is altitude sickness?
- Symptoms: mild, moderate, severe
- Prevention: acclimatisation, hydration, pace
- Diamox: should you take it?
- What happens on the trail if you get sick
- Helicopter evacuation
- Which Nepal treks carry the highest risk?
What Is Altitude Sickness?
Altitude sickness, medically called Acute Mountain Sickness (AMS), occurs when your body doesn’t 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’re 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.
Symptoms: How to Recognise Each Stage
Mild AMS
The early signs are easy to dismiss as tiredness from a long day of trekking. That’s why they’re dangerous. Mild AMS symptoms include:
- Headache, the most reliable early indicator
- Nausea or loss of appetite
- Fatigue beyond what the day’s exertion warrants
- Dizziness or light-headedness
- Disturbed sleep, waking frequently
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’re worsening, descend.
Moderate AMS
Moderate AMS means the body is struggling and rest alone won’t 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 that develops 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 to see if it improves.
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 300-500m per day in sleeping altitude, with a rest day every 3-4 days. This is why a well-structured EBC itinerary takes 14 days rather than 10. Those extra days aren’t padding; they’re 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.
The classic “climb high, sleep low” principle also applies within each day: it’s fine to trek to a higher point during the day as long as you return to sleep at a lower altitude.
2. Hydration
Dehydration worsens AMS symptoms significantly and is easy to let happen at altitude. You’re breathing harder, the air is dry, and you may not feel thirsty. Aim for 3-4 litres of water per day on the trail. Urine colour is the best indicator: pale yellow means you’re 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. One beer at Namche won’t end your trek, but regular drinking at altitude is a genuine risk factor.
3. Pace yourself on the trail
Move slowly. This is harder than it sounds. Most trekkers are fit, motivated people who feel fine and want to push. 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.
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’s 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. There is no single right answer. Dosage, timing, and suitability depend on individual health history, any other medications you’re taking, and whether you have sulfa allergies (Diamox is a sulfa drug). Some doctors recommend it preventively from day one at altitude; others prefer to use it only if symptoms appear.
What we strongly recommend: speak to your GP or a travel medicine clinic before you leave home. Tell them your planned itinerary, the maximum altitude you’ll reach, and ask specifically about Diamox. A prescription is easy to get in most countries, and having it available on the trail even if you don’t end up using it is sensible.
Common side effects include increased urination (it’s a mild diuretic) and tingling in the fingers and toes. These are normal and not a reason to stop taking it.
Do not buy Diamox in Kathmandu or on the trail without a prescription and without understanding the correct dosage. It’s available in Nepal pharmacies but self-prescribing at altitude without medical guidance is not recommended.
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 clips onto your finger and measures blood oxygen saturation (SpO2), the single most reliable on-the-ground indicator of how well your body is acclimatising. At sea level, normal SpO2 is 95-100%. At altitude, readings drop, typically to 85-95% in the Khumbu region and slightly higher on lower-altitude routes like Langtang or Poon Hill. A reading below 80% combined with symptoms is a clear signal that something is wrong.
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. Encourage the trekker to drink water and eat if possible.
- Provide general supportive medication. Guides carry basic medications including pain relief for headache. This addresses comfort but not the underlying cause.
- If symptoms worsen or don’t improve, descend. Even 300-500m 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, including sections of the Annapurna and Langtang routes, guides arrange horse or mule transport for trekkers who cannot walk down safely. This is not a last resort; it’s used whenever descent needs to happen faster than a trekker can manage on foot.
- Helicopter evacuation for severe cases. If symptoms indicate HACE or HAPE, or if the trekker cannot descend safely by other means, evacuation is arranged immediately. MountainKick works with Air Dynasty and other operators depending on availability and the trekker’s location. Evacuation from most points on Nepal’s main routes can be arranged within 1-3 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, not a box-ticking exercise. For guidance on what your policy must cover, read our Nepal trekking insurance guide.
Helicopter Evacuation in Nepal: What to Expect
Nepal has a well-established helicopter rescue infrastructure. Air Dynasty is one of the main operators, alongside several others. Availability depends on weather, location, and which aircraft are operational at the time. Your guide coordinates the evacuation; your job is to stay calm and follow instructions.
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: $3,000-6,000 USD depending on pickup location and distance. With valid insurance covering helicopter evacuation, it’s 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.
Which Nepal Treks Carry the Highest AMS Risk?
Risk increases with maximum sleeping altitude and the speed of ascent. Here’s how MountainKick’s main routes compare:
| Trek | Max sleeping altitude | AMS risk level | Acclimatisation days |
|---|---|---|---|
| Everest Base Camp | 5,364m (Gorakshep) | High | 2 (Namche + Dingboche) |
| Annapurna Circuit | 4,800m (High Camp) | Moderate to High | 1-2 (Manang) |
| Annapurna Base Camp | 4,130m (ABC) | Moderate | Built into ascent pace |
| Manaslu Circuit | 5,106m (Larkya La) | High | 1-2 (Samdo/Dharamsala) |
| Langtang Valley | ~4,984m (Tserko Ri) | Moderate | 1 (Kyanjin Gompa) |
| Poon Hill | 3,210m (Poon Hill) | Low | None needed |
Previous altitude experience helps. If you’ve trekked above 4,000m before without problems, that’s useful information. But it’s not a guarantee. AMS can affect the same person differently on different trips depending on speed of ascent, hydration, fatigue, and other factors.
Common Questions
Can fit people get altitude sickness?
Yes, and they often do. Cardiovascular fitness doesn’t protect against AMS. In fact, very fit trekkers sometimes move faster than they should and ascend too quickly, increasing their risk. The mountains don’t care about your VO2 max.
What if I’ve 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 doesn’t 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 altitude does the trek start at?
For EBC, the trek starts at Lukla (2,860m), already at an altitude where some trekkers feel mild effects. For ABC, it starts around Nayapul (1,070m), low enough that the ascent is gradual and AMS risk in the first few days is minimal.
Planning a trek and want to know more about how we handle altitude safety on your specific route?
WhatsApp: +977 985 118 2718
or use our enquiry form.
Further Reading
- Trekking in Nepal: The Complete Guide
- Everest Base Camp Trek Cost 2026
- Annapurna Base Camp Trek Cost 2026
- Travel Insurance for Trekking Nepal: What Your Policy Must Cover
- Annapurna Circuit vs ABC: Which Trek Should You Do?
