Altitude Sickness in Nepal: Prevention, Symptoms & What Actually Works

Altitude sickness — clinically Acute Mountain Sickness, or AMS — is the single most common reason trekkers abandon their Nepal itinerary mid-route. It affects roughly 40% of trekkers who sleep above 3,000 metres, and here is the uncomfortable truth: fitness has almost nothing to do with susceptibility. Olympians get AMS; couch trekkers reach Kala Patthar without a headache. Your acclimatisation response is largely genetic, and nobody knows how theirs will behave until they are up there.

The good news: AMS is predictable, preventable in many cases, and almost always manageable when you know what to watch for. Our guides have led more than 5,000 trekking groups across high-altitude Nepal — to 5,000 m-plus hundreds of times — and this guide distils what actually works, with no filler and no false reassurance. It aligns with the high-altitude health guidance published by the World Health Organization and the treatment standards of the Wilderness Medical Society and the Himalayan Rescue Association.

What Is Altitude Sickness?

The umbrella term covers three conditions of increasing severity:

The severity spectrum runs from mild inconvenience (mild AMS) to life-threatening within hours (HACE/HAPE). Knowing which rung of the ladder you are on is the critical skill.

Symptoms to Watch For

Mild to moderate AMS:

• Headache — usually throbbing, worse when bending over or lying flat
• Nausea or vomiting
• Dizziness or light-headedness
• Loss of appetite (the clearest early warning sign in our guides' experience)
• Disrupted sleep — vivid dreams, frequent waking, Cheyne-Stokes (periodic) breathing
• General fatigue beyond what the day's exertion would explain

The Golden Rule

Everything in altitude medicine returns to one principle: if your symptoms are not improving — or are worsening — after 24 hours at the same altitude, descend.

Never ascend to sleep higher with unresolved symptoms from the previous day. The classic mistake is feeling slightly better in the morning after a rough night and pushing on, only to deteriorate severely by afternoon. The mountain will still be there when you are acclimatised. No summit, base-camp photo, or sunk-cost itinerary is worth HACE or HAPE.

The corollary: mild AMS that genuinely improves with rest at the same altitude does not necessarily mean abandoning your trek — it means acclimatising properly before moving higher.

Acclimatisation Schedules That Work

The standard guideline — above 3,000 m, raise your sleeping elevation by no more than 300–500 m per day, with a rest day every third or fourth day — is the right starting point. But every major route has specific acclimatisation nodes that experienced guides build around:

• Everest Base Camp: the rest day at Namche Bazaar (3,438 m) is non-negotiable — spend two nights minimum, with a day hike to the Everest View Hotel (3,880 m) and back: higher by day, sleep lower at night. A second rest day at Dingboche (4,360 m) or Pheriche repeats the trick before Lobuche and Gorakshep. Our 14-day EBC itinerary is built around these exact rest points; see also our Everest trekking guide and the 2026 EBC cost breakdown.
• Annapurna Base Camp: the relatively rapid gain — you can reach 4,130 m from Pokhara in six days — makes listening to your body essential. Read our ultimate ABC guide and book the classic 6-day ABC trek, or warm up on the lower Ghorepani Poon Hill trek first.
• Manaslu Circuit: the rest day at Samagaon (3,520 m), with an optional hike to Manaslu Base Camp (4,400 m), is the key preparation before crossing the Larkya La at 5,106 m on the 14-day Manaslu Circuit.

Acclimatisation is not just resting. Light activity at altitude — short hikes, walks around the village — beats complete inactivity. The old mantra holds: climb high, sleep low.

Does Diamox (Acetazolamide) Work?

Honest answer: yes, as a preventive measure, and meaningfully so. Acetazolamide stimulates faster, deeper breathing, which raises blood oxygen and speeds the body's natural acclimatisation — compressing the ventilatory adaptation that normally takes three to five days into about one. It does not mask AMS; it genuinely helps you adapt.

Practical guidance from our team, consistent with current Wilderness Medical Society dosing:

• Dosage: 125 mg twice daily is the standard prophylactic dose; 250 mg twice daily is used for faster ascents. Most trekkers do well on 125 mg with fewer side effects.
• Start time: begin the day before your first significant ascent, not after symptoms appear, and continue for two to four days at the target altitude.
• Side effects: increased urination (expected, harmless), tingling in fingers and toes, and fizzy drinks tasting flat. Annoying, not dangerous.
• Sulfa allergy: Diamox is a sulfonamide — if you have a sulfa allergy, avoid it and discuss alternatives (e.g. dexamethasone) with your doctor before travel.
• Not a substitute for acclimatisation: it reduces risk and severity; it does not eliminate AMS. Never treat it as permission to rush your ascent.

Hydration, Alcohol & Sleep

Three overlooked but critical factors:

• Water: drink 3–4 litres per day above 3,000 m. Dehydration worsens AMS, and the cold, dry air accelerates fluid loss even when you do not feel thirsty. Urine colour is your guide — aim for pale yellow, not dark amber.
• Alcohol: avoid it entirely above 3,000 m. Alcohol suppresses respiration during sleep, dropping blood oxygen at the worst possible time. One beer at Namche can feel like three the next morning.
• Diamox & sleep: Diamox can mean more night-time urination. Some trekkers shift the second dose to late afternoon rather than bedtime — worth asking your doctor.
• Sleeping tablets: many sleep aids, particularly benzodiazepines, suppress night-time breathing and are contraindicated at altitude. Do not self-medicate for sleep above 3,000 m without medical advice.

How Our Guides Handle Altitude Emergencies

On routes above 3,500 m, Travel Himalaya Nepal guides carry and use pulse oximeters to track blood-oxygen saturation (SpO₂) as a routine part of each day's check-in. A reading below 80% SpO₂ at rest, or a sharp drop from the previous day's baseline, triggers our emergency protocol:

1. Immediate rest; no further ascent.
2. Supplemental oxygen from the emergency kit carried on all high-altitude departures.
3. If no improvement within one hour, immediate descent — assisted if necessary.
4. Satellite communication with our Pokhara operations team to coordinate helicopter evacuation if ground descent is not viable.

Our guides hold Wilderness First Aid training and high-altitude medicine certification from the Himalayan Rescue Association. We have maintained a zero-fatality record across more than 5,000 guided treks — because we run the protocol every time, for every trekker, regardless of schedule pressure.

Travel Insurance for Altitude Emergencies

A helicopter evacuation from above 4,000 m in Nepal costs between USD 5,000 and USD 15,000 — and in 2026, top-end rescues above 5,000 m commonly land at the higher end of that range, depending on altitude, weather and the number of flight legs. This is not a bill you want uninsured.

We strongly recommend a policy that explicitly covers:

• High-altitude trekking — specify your route's maximum altitude (EBC reaches 5,545 m at Kala Patthar)
• Emergency helicopter evacuation, with a medical-evacuation limit of at least USD 100,000
• Medical repatriation and trip cancellation due to medical emergency

Frequently Asked Questions

Do Not Let AMS Fear Stop You

Altitude sickness is real, common, and deserves respect — but it is not a reason to avoid Nepal's high trails. It is a reason to plan them intelligently. Thousands of trekkers complete Everest Base Camp, Annapurna Base Camp and the Manaslu Circuit every year without serious altitude complications, because they acclimatise properly, listen to their bodies, and travel with guides who know what to watch for. For wider planning, see our best time to trek Nepal in 2026 guide and our notes on responsible trekking.

Planning to add a summit to your Nepal trip? Browse all Nepal peak climbing packages — Island Peak, Mera Peak, Lobuche East, and more.