Altitude sickness is the single most serious health risk on Nepal treks. It does not discriminate by fitness, age, or experience. A trained marathon runner can be floored by AMS at 3,500m while a sedentary first-timer sails through to 5,000m. The only reliable predictor is your body's individual response — which you cannot know in advance. What you can control is preparation and response.
The Three Conditions: AMS, HACE, HAPE
Acute Mountain Sickness (AMS) is the common form — headache, nausea, fatigue, dizziness, and difficulty sleeping above 2,500m. It affects up to 50% of trekkers on routes like the Annapurna Circuit and Everest Base Camp. Mild AMS resolves with rest and no further ascent. It is not dangerous by itself.
High Altitude Cerebral Oedema (HACE) is AMS that has progressed to brain swelling. Symptoms: severe headache that does not respond to ibuprofen, loss of coordination (the "drunk walk test"), confusion, drowsiness. HACE is a medical emergency — immediate descent is the only treatment. Do not wait to see if it improves.
High Altitude Pulmonary Oedema (HAPE) is fluid accumulation in the lungs. Symptoms: breathlessness at rest, dry cough that progresses to frothy/pink sputum, inability to walk at a normal pace on flat ground. HAPE is the most common cause of altitude-related death. Immediate descent is mandatory. Our guides carry nifedipine for emergency treatment while evacuation is arranged.
Prevention: The Golden Rule
The golden rule of altitude trekking is deceptively simple: do not ascend more than 500m per sleeping altitude per day above 3,000m, and include a rest day every 1,000m of gain. Our itineraries for the Annapurna Circuit, Everest Base Camp, and Manaslu Circuit are all built around this protocol. We will not rush to meet a flight connection.
- Ascend slowly — your body needs time to produce more red blood cells
- Sleep lower than you walk ("climb high, sleep low")
- Drink 4+ litres of water per day
- Avoid alcohol above 3,000m
- Eat even when you have no appetite — altitude suppresses hunger
- Do not take sleeping tablets — they can suppress breathing at altitude
Diamox (Acetazolamide) — Should You Take It?
Diamox is a prescription medication that accelerates acclimatisation by stimulating faster breathing. It is not a cure for altitude sickness — it reduces the risk of AMS when ascending. Some trekkers take it prophylactically from 2,500m; others take it only if early AMS symptoms appear. It has side effects (tingling in fingers and toes, increased urination, occasional nausea) and is not suitable for everyone — particularly those with sulfa allergies.
Our recommendation: consult your doctor 4–6 weeks before departure. Have a prescription ready but decide whether to use it based on how your acclimatisation progresses. Your guide can advise in the field. We do not make Diamox decisions for you, but we do carry it for emergency use.
What Our Guides Do
Every Annapurna Trekking guide carries a pulse oximeter and checks group oxygen saturation twice daily from 3,000m onward. Our turn-back protocols are non-negotiable: any trekker showing HACE or HAPE symptoms descends immediately, without debate. We carry supplemental oxygen from Manang on the Circuit and from Namche on the EBC route. Our Kathmandu office is reachable 24/7 for helicopter evacuation coordination.
Helicopter Evacuation
If your situation requires helicopter evacuation — and altitude emergencies often do — the cost runs from USD 3,500 to USD 8,000 depending on location. This is why travel insurance with specific helicopter evacuation cover at your trek's maximum altitude is mandatory for all our trips. We check your insurance at the pre-trek briefing. Do not risk it.
