The Annapurna Base Camp Trek reaches 4,130m — a significant altitude where Acute Mountain Sickness (AMS) is a genuine risk. The good news: the ABC route has one of the most naturally well-designed acclimatisation profiles of any Nepal trek. If you follow the protocol, the overwhelming majority of trekkers reach base camp without serious altitude problems.
The ABC Altitude Profile — Where the Risk Zones Are
Understanding each stage of the route helps you know when to be alert:
- Nayapul (1,070m) to Ghorepani (2,874m): No meaningful altitude risk. This is where many trekkers start. The climb is physically demanding but altitude is not the concern here.
- Poon Hill (3,210m): Minor headaches possible for some trekkers. Not a risk stage — you are not sleeping here on the standard itinerary.
- Chhomrong (2,160m): Safe. The route descends back from Ghorepani before climbing again.
- Deurali (3,230m): First night above 3,000m on many itineraries. Mild AMS symptoms — headache, reduced appetite — are common and manageable. Do not ascend the next day if symptoms persist.
- Annapurna Base Camp (4,130m): Significant AMS risk. Symptoms affect a meaningful percentage of trekkers. Our guides monitor oxygen saturation here and the protocol is clear: if you are symptomatic at base camp, we descend to Machhapuchhre Base Camp (3,700m) or lower immediately.
The Three Forms of Altitude Illness
Acute Mountain Sickness (AMS) — headache plus one or more of: nausea, fatigue, dizziness, difficulty sleeping. Mild AMS at Deurali is common and resolves with rest and no further ascent. AMS at base camp that persists or worsens requires immediate descent.
High Altitude Pulmonary Oedema (HAPE) — fluid in the lungs. Symptoms: breathlessness at rest, persistent cough, inability to walk at normal pace. A medical emergency — descend immediately and call for helicopter evacuation if the person cannot walk. Rare on ABC but possible.
High Altitude Cerebral Oedema (HACE) — fluid in the brain. Symptoms: loss of coordination (the "drunk walk" test — can the person walk a straight line?), confusion, extreme fatigue. The most dangerous form. Descend immediately. Extremely rare at ABC's altitude but must be recognised.
Prevention Protocol for the ABC Trek
- Ascend gradually: Our itinerary is designed for this — never more than 500m of sleeping altitude gain per day above 3,000m.
- Hydrate aggressively: Minimum 3–4 litres of water per day from Ghorepani onward. Dehydration accelerates AMS.
- No alcohol above 2,500m: It suppresses the respiratory drive and impairs the body's response to low oxygen.
- Eat even when appetite is reduced: Altitude commonly suppresses hunger. Force yourself to eat — your body needs fuel to function at elevation.
- Diamox (acetazolamide): Discuss with your doctor before departure. We carry it and can advise on the trail — it is effective at reducing AMS symptoms when used correctly.
The 2015 ABC Disaster — What Happened and What Changed
In October 2015, a snowstorm and avalanche caught hundreds of trekkers in the Annapurna region, killing 43 people. This was a weather event, not primarily an altitude illness event. In response, the Nepal government and TAAN (Trekking Agents Association of Nepal) improved weather warning systems and emergency communication infrastructure along the ABC route. Our guides carry satellite communication and monitor weather forecasts in real time.
When to Turn Back
The single most important altitude safety decision is turning back when the protocol demands it, regardless of how close to base camp you are. Our guides follow the ISMM (International Society of Mountain Medicine) protocol without exception: if your oxygen saturation is below 80% with symptoms, we descend. There is no summit worth a serious altitude illness event. Base camp will still be there on your next visit.
For the full medical context and emergency procedures on the ABC trek, see our Complete Altitude Sickness Guide. To start planning your trek, see the Annapurna Base Camp Trek page.
