Altitude sickness on the Annapurna Circuit trek is the most serious health risk on the route — and the most preventable. The circuit reaches 5,416m at Thorong La Pass, spending two nights above 4,000m at Yak Kharka and Thorong Phedi. At this altitude the body receives roughly 53% of the oxygen available at sea level, and Acute Mountain Sickness can affect any trekker regardless of fitness, age, or prior experience at altitude. Furthermore, the circuit’s long duration means cumulative altitude stress builds over 8–9 days of continuous ascent before the pass — making the acclimatisation schedule more important here than on shorter Nepal treks. Consequently, this guide covers every aspect of altitude management on the circuit: the symptoms, the prevention protocol, the Manang acclimatisation strategy, and the emergency procedures that Mountain Hike Nepal applies on every departure.
What’s Inside This Guide
- What Is Altitude Sickness?
- AMS Symptoms — Mild, Moderate, Severe
- Prevention — What Actually Works
- The Manang Acclimatisation Strategy
- Diamox — Should You Take It?
- Thorong La — the Altitude Peak
- When to Descend — Emergency Protocol
- Helicopter Evacuation on the Circuit
- Frequently Asked Questions
- Related Planning Guides
Altitude Sickness on the Annapurna Circuit Trek — What It Is
Acute Mountain Sickness (AMS) occurs when the body ascends faster than it can adapt to reduced oxygen availability. Above 2,500m, every 100m of altitude gain reduces available oxygen by approximately 0.5%. At Thorong La Pass (5,416m) the body receives roughly 53% of sea-level oxygen. Furthermore, altitude sickness on the Annapurna Circuit trek differs from shorter Nepal treks because the circuit spends more consecutive days in altitude territory — 8 days of continuous ascent from Chame to Thorong Phedi — which means cumulative altitude stress compounds in a way it cannot on a 2-day high-altitude section. Consequently, altitude management on the circuit is not just about Thorong La crossing day — it is an 8-day physiological process that starts the moment the jeep reaches Chame.
Who gets altitude sickness on the circuit
Anyone ascending to altitude can develop AMS. Prior high-altitude experience reduces but never eliminates the risk. Fit trekkers are not immune — in fact, high fitness can increase risk because fit trekkers tend to push pace, reducing acclimatisation time. Furthermore, there is no reliable way to predict individual AMS susceptibility from sea level — blood type, fitness, age, and previous altitude performance are all poor predictors. Consequently, the only effective protection on the circuit is following the acclimatisation schedule, drinking consistently, and reporting every symptom to the guide immediately rather than hoping it resolves overnight.
Altitude Sickness on the Annapurna Circuit Trek — Symptoms
Mild AMS — Common and Manageable
| Symptom | When It Typically Appears | Action |
|---|---|---|
| Headache | First night above 3,000m — often at Manang or Yak Kharka | Paracetamol + 500ml water — report if not resolved in 2 hours |
| Fatigue beyond expected effort | Above 3,500m — normal and expected | Rest, hydrate — do not push pace |
| Reduced appetite | Above 3,500m consistently | Eat carbohydrates anyway — especially at Thorong Phedi |
| Disturbed sleep | Yak Kharka and Thorong Phedi | Normal response — not a concern alone |
| Mild dizziness on exertion | Above 4,000m on uphills | Slow pace — rest until it passes |
Moderate AMS — Report Immediately to Your Guide
| Symptom | Significance | Action |
|---|---|---|
| Persistent headache — paracetamol and water do not resolve within 2 hours | AMS progressing — do not ascend further | Report to guide immediately — rest at current altitude |
| Nausea or vomiting | Moderate AMS indicator | Report immediately — no further ascent until resolved |
| Breathlessness at rest | Concerning above 3,500m | Report immediately — may require descent |
| Extreme fatigue disproportionate to effort | Body struggling with altitude | Rest — reassess with guide before any further ascent |
Severe AMS — Emergency — Descend Immediately
| Symptom | Condition | Action |
|---|---|---|
| Loss of coordination or balance (ataxia) | HACE — High Altitude Cerebral Edema | Descend immediately — do not wait for morning |
| Confusion or altered behaviour | HACE indicator | Emergency descent — helicopter if needed |
| Persistent cough with frothy or pink sputum | HAPE — High Altitude Pulmonary Edema | Emergency descent — helicopter immediately |
| Severe breathlessness at rest | HAPE indicator | Emergency descent — do not wait for any reason |
HACE and HAPE are life-threatening. The correct response to either is immediate descent — not medication, not rest, not waiting for morning. Furthermore, Mountain Hike Nepal guides carry pulse oximeters and monitor oxygen saturation from Yak Kharka onward on every departure. Consequently, any saturation reading below 80% at altitude triggers immediate medical assessment and potential descent regardless of how the trekker feels subjectively.
Prevention — What Actually Works
Hydration — the single most important action
Drink 3–4 litres of water every day from Manang onward without exception. Altitude suppresses thirst — the body needs it regardless of whether you feel thirsty. Furthermore, dehydration at altitude accelerates AMS symptoms significantly — it is the most common and most easily prevented contributing factor to altitude sickness on the Annapurna Circuit. Consequently, set a deliberate drinking schedule above Manang: 500ml by mid-morning, 500ml by lunch, 500ml by mid-afternoon, 500ml by evening. This single habit prevents the majority of altitude headaches on the circuit.
Pace — the guide’s conversational pace is not optional
Walking at a pace where you can speak a full sentence without pausing for breath is the Mountain Hike Nepal standard from Manang onward. This feels slow at Yak Kharka and feels exactly right at Thorong La above 5,000m. Furthermore, trekkers who push ahead of the guide on Days 7 and 8 consistently arrive at Thorong Phedi with accumulated altitude stress that surfaces on crossing day. Consequently, follow the guide’s pace from the first step above Manang — not because it feels necessary, but because the cost of ignoring it appears 2 days later at 5,000m.
Eat at altitude even when appetite disappears
Altitude suppresses appetite significantly above 4,000m — most trekkers at Thorong Phedi feel like eating very little before the crossing day. Eat anyway. Carbohydrates digest more easily than protein and fat at altitude — dal bhat, noodles, and tsampa porridge are the right choices above 4,000m. Furthermore, garlic soup appears on every teahouse menu above Manang — warm, hydrating, and calorie-dense regardless of its AMS prevention reputation. Consequently, order it at every stop above Manang and use the evening meal at Thorong Phedi as the final fuel loading before the 4am start.
The Manang Acclimatisation Strategy
The acclimatisation day in Manang at 3,540m is the most important single day on the entire circuit for altitude safety. Missing it is the most common reason trekkers develop serious AMS above 4,000m — not fitness, not prior experience, but skipping Manang.
What Day 6 in Manang should look like
Morning: hike to Gangapurna Lake at 3,700m — a 2–3 hour round trip that provides “climb high, sleep low” acclimatisation and one of the finest viewpoints on the circuit. The 160m altitude gain above Manang prepares the body for the larger altitude steps ahead. Furthermore, the HRA (Himalayan Rescue Association) runs a free altitude medicine lecture in Manang every afternoon — attend it. The lecture covers AMS recognition, Diamox guidance, and the specific risks of the Thorong La crossing in language directly relevant to the circuit. Consequently, Day 6 at Manang is not a rest day — it is a specific preparation day with a morning hike, an afternoon lecture, and an early evening meal before the altitude push begins on Day 7.
The Gangapurna Lake hike as acclimatisation
Gangapurna Lake at 3,700m sits directly beneath the south face of Gangapurna (7,455m) — a glacial lake with the glacier and icefall reflected in the water on calm mornings. It is the most popular and most recommended rest-day destination in Manang, and the most effective acclimatisation hike on the circuit. Furthermore, the lake combines genuine visual reward with the specific altitude gain the body needs before Yak Kharka. Consequently, every trekker on every Mountain Hike Nepal circuit departure includes the Gangapurna Lake hike on acclimatisation day — it is not optional.
Diamox — Should You Take It on the Circuit?
Acetazolamide (Diamox) is a prescription medication that accelerates acclimatisation by stimulating the breathing rate. It is effective and widely used on high-altitude treks including the Annapurna Circuit.
The decision is medical and personal. Side effects include increased urination, tingling in hands and feet, and occasional nausea — not serious for most trekkers but uncomfortable for some. Furthermore, Diamox does not eliminate AMS risk — it reduces it. It also does not substitute for pace control, hydration, or the Manang acclimatisation day. Consequently, discuss Diamox with your doctor at home at least 4 weeks before departure — not in Kathmandu on arrival day when it is too late to test your response.
Who benefits most from Diamox on the circuit
Trekkers with a history of AMS on previous high-altitude trips, those ascending from sea level with limited preparation time, anyone whose doctor specifically recommends it, and trekkers who want to carry it as rescue medication only — starting if symptoms develop above Yak Kharka rather than as prophylaxis from the start. Furthermore, the HRA clinic in Manang can provide altitude-specific guidance during the acclimatisation day. Consequently, the Manang HRA clinic is the best place to ask about Diamox on the circuit — from doctors who know this specific route.
Altitude Sickness on the Annapurna Circuit Trek — Thorong La Crossing Day
Thorong La at 5,416m is the highest altitude point on the circuit and the day where AMS risk is greatest. Specific protocol applies from the moment the alarm sounds at 4am.
What makes crossing day high-risk
The body at 5,000m+ operates at 53% sea-level oxygen. The ascent from Thorong Phedi (4,450m) to the pass (5,416m) gains 966m at an altitude where every 100m feels harder than the last. The pre-dawn cold (-10°C to -15°C) adds respiratory demand. Furthermore, trekkers who develop AMS symptoms between Thorong Phedi and the pass face a genuine dilemma — the summit is above, but descent is the medically correct response. Consequently, Mountain Hike Nepal applies a strict no-ascent-with-AMS protocol: if any trekker shows active symptoms at Thorong Phedi, the team does not proceed until the guide clears them. No exceptions, no schedule pressure.
Signs that mean turn back — not push through
Persistent headache at Thorong Phedi that paracetamol and water do not resolve within 2 hours. Nausea on the ascent above 5,000m. Loss of coordination at any point. Breathlessness at rest on the trail. Furthermore, turning back from Thorong Phedi is not a failure — it is the correct medical decision when symptoms are present. The pass will be there on a future trip. HACE and HAPE will not wait. Consequently, any trekker who turns back from Thorong La on Mountain Hike Nepal’s recommendation descends to Manang where the HRA clinic can assess and advise on next steps including helicopter evacuation if needed.
When to Descend — Emergency Protocol
The golden rule of altitude medicine: if in doubt, descend. Never ascend with active AMS symptoms. A descent of 300–500m relieves symptoms within hours. Furthermore, Mountain Hike Nepal applies a strict no-ascent-with-AMS policy on every circuit departure — the guide’s assessment overrides any trekker’s personal preference or schedule pressure. Consequently, the guide’s decision on this question is final and non-negotiable.
Signs that require immediate descent — not morning
Loss of coordination or balance, confusion or unusual behaviour, persistent cough with frothy sputum, or severe breathlessness at rest. These indicate HACE or HAPE — both life-threatening conditions where descent is the only treatment. Furthermore, none of these conditions improve with rest at altitude — only descent addresses the cause. Consequently, these signs at any point on the circuit — Yak Kharka, Thorong Phedi, the pass, or anywhere on the approach — trigger immediate descent and helicopter evacuation assessment.
Helicopter Evacuation on the Annapurna Circuit
Mountain Hike Nepal arranges helicopter evacuation from any point on the circuit when needed — Thorong Phedi, the pass approach, Manang, or anywhere on the route with a landable area. The helicopter flies directly to a hospital in Kathmandu or Pokhara for immediate medical treatment. Furthermore, arrival from the nearest landable point is typically 2–4 hours in good weather — faster than any descent on foot from the upper circuit. Consequently, no trekker on this route ever faces the choice between walking out with a serious condition and waiting for road transport.
Your travel insurance covers helicopter evacuation costs when the policy explicitly includes trekking above 5,000m. Mountain Hike Nepal confirms this insurance documentation before every departure. For helicopter return or emergency options: Chat with us on WhatsApp →
Frequently Asked Questions
Mild AMS symptoms — headache, reduced appetite, disturbed sleep — are common and expected above 3,500m. Most trekkers experience at least one mild symptom between Yak Kharka and Thorong Phedi. However, serious altitude sickness on the Annapurna Circuit trek requiring descent affects a much smaller percentage of trekkers who follow the acclimatisation schedule. Furthermore, the Manang rest day and Gangapurna Lake hike provide the most complete acclimatisation protocol of any standard Nepal trekking route. Consequently, trekkers who follow the itinerary and maintain hydration have a low serious AMS risk despite crossing a 5,416m pass.
Different. EBC is harder on sustained altitude — two nights above 5,000m at Gorakshep where oxygen sits at 53% of sea level for consecutive days. The circuit reaches 5,416m at the pass but descends immediately — only one night above 4,450m at Thorong Phedi before crossing. Furthermore, the circuit’s 8-day gradual ascent from Chame to Thorong Phedi provides more acclimatisation time than EBC’s approach. Consequently, first-time high-altitude trekkers often find the circuit’s altitude more manageable than EBC — despite crossing a higher pass — because the descent is immediate and the acclimatisation schedule is longer.
Mountain Hike Nepal guides apply a no-ascent-with-AMS protocol — if active symptoms appear at Thorong Phedi or on the ascent, the guide stops the team and assesses. If descent is the correct decision, the team descends to Manang where the HRA clinic provides assessment. Furthermore, if helicopter evacuation is needed, Mountain Hike Nepal arranges it within hours from the nearest landable point. Your travel insurance covers the cost when the policy explicitly includes trekking above 5,000m and helicopter evacuation. Consequently, developing AMS on the circuit is manageable when symptoms are reported early and the protocol is followed.
Related Planning Guides
- Annapurna Circuit Package — Full 15-day expedition from USD 828 per person
- Elevation and Altitude Guide — Day-by-day altitude profile
- Day-by-Day Itinerary — Acclimatisation schedule in full detail
- How Hard Is the Circuit? — Thorong La difficulty guide
- Circuit for Beginners — Altitude preparation for first-timers
- Best Time to Trek — How season affects Thorong La conditions
- Circuit Cost 2026 — Insurance requirements in the budget
Understand It. Prevent It. Report It Early.
Altitude sickness on the Annapurna Circuit trek is the most serious risk on this route and the most preventable. Attend the Manang HRA lecture. Hike to Gangapurna Lake on Day 6. Drink 3–4 litres above Manang every day. Follow the guide’s conversational pace from Yak Kharka. Report every headache immediately — not after dinner, not in the morning. Do not ascend with active symptoms. The acclimatisation schedule works. The protocol works. Follow both and Thorong La at 5,416m is achievable — one of the finest and most rewarding moments any prepared trekker will experience anywhere.
Mountain Hike Nepal has managed altitude safety on the Annapurna Circuit since 2018 as a licensed local operator in Kathmandu. When you contact us, you speak directly with the team that handles this on the trail every season. Consequently, any question about AMS prevention, the Manang protocol, Diamox, or helicopter evacuation gets a real answer from people who were last at Thorong La recently.
The full package starts at USD 828 per person for groups of 8–10, USD 898 for 4–6, USD 998 for 2–3, and USD 1,198 for solo trekkers. All permits and transport included. Helicopter evacuation protocol included on every departure.
View the full Annapurna Circuit Trek package →
Questions about altitude sickness prevention, the Manang acclimatisation day, or emergency protocols? We respond within 12 hours and give straight answers.