Altitude sickness — also called Acute Mountain Sickness (AMS) — is one of the most important health risks to understand before trekking to Everest Base Camp. It affects a significant number of trekkers above 3,500m and, in severe cases, can be life-threatening. The good news: altitude sickness is largely preventable with the right acclimatisation schedule, awareness of symptoms, and willingness to descend if needed.
This guide covers everything you need to know about altitude sickness on the EBC trek: what it is, how to recognise it, how to prevent it, and what to do if you or a member of your group is affected.
What Is Altitude Sickness?
Altitude sickness occurs when your body doesn’t adapt fast enough to the reduced oxygen levels at high elevation. As you ascend above 2,500m, the partial pressure of oxygen in the air decreases. Your body responds by breathing faster and producing more red blood cells, but this adjustment takes time. If you ascend too quickly, your body can’t keep up, and symptoms of AMS develop.
Altitude sickness exists on a spectrum:
- Acute Mountain Sickness (AMS) — mild to moderate, the most common form
- High Altitude Cerebral Edema (HACE) — severe, involving fluid on the brain; a medical emergency
- High Altitude Pulmonary Edema (HAPE) — severe, involving fluid in the lungs; the most common cause of altitude-related death
Symptoms of Acute Mountain Sickness (AMS)
Mild to moderate AMS is common on the EBC trek, particularly after arriving at Namche Bazaar (3,440m) and again above Dingboche (4,410m). Most trekkers experience at least some mild symptoms at altitude.
Common AMS symptoms include:
- Headache (the most common early symptom)
- Fatigue and weakness
- Dizziness or lightheadedness
- Nausea and reduced appetite
- Difficulty sleeping (insomnia is very common at altitude)
- Shortness of breath on exertion
Mild AMS symptoms typically improve with rest at the same altitude and adequate hydration. They should not be treated by ascending further — if symptoms are present, stay where you are until they resolve.
The Lake Louise Score is a commonly used tool to assess AMS severity. A headache at altitude plus one or more additional symptoms (fatigue, gastrointestinal symptoms, dizziness, poor sleep) indicates probable AMS and warrants rest, monitoring, and no further ascent until symptoms clear.
High Altitude Cerebral Edema (HACE)
HACE is a severe, life-threatening form of altitude illness caused by fluid accumulation in the brain. It typically develops from untreated or ignored AMS. HACE is a medical emergency requiring immediate descent.
Symptoms of HACE include:
- Severe headache that does not respond to painkillers
- Confusion, disorientation, or irrational behaviour
- Loss of coordination (ataxia) — inability to walk in a straight line
- Drowsiness progressing to unconsciousness
A simple field test for HACE: ask the trekker to walk heel-to-toe in a straight line. Inability to do so is a serious warning sign. If HACE is suspected, descend immediately — do not wait for morning. Every hour matters.
High Altitude Pulmonary Edema (HAPE)
HAPE is caused by fluid building up in the lungs at altitude. It is the most common cause of altitude-related death and can develop rapidly, even in people without prior AMS symptoms. HAPE is a medical emergency requiring immediate descent and, where possible, supplemental oxygen.
Symptoms of HAPE include:
- Shortness of breath at rest (not just on exertion)
- Extreme fatigue disproportionate to effort
- Persistent dry cough, possibly producing pink or frothy mucus
- Bluish lips or fingernails (cyanosis)
- Gurgling or rattling breath sounds
HAPE can progress from mild symptoms to critical condition within hours. If HAPE is suspected, descend immediately, administer supplemental oxygen if available, and call for helicopter evacuation.
The Golden Rule: Never Ascend with Symptoms
The single most important rule for altitude safety on any high-altitude trek is: never ascend to a higher sleeping altitude if you have AMS symptoms. If you have a headache, nausea, or dizziness at your current altitude, rest for a day. Only proceed once your symptoms have fully resolved.
Even if your group is moving on and you feel social pressure to keep up, your safety must come first. A good guide will support this decision — if yours doesn’t, that is a red flag about the guiding quality.
How to Prevent Altitude Sickness on the EBC Trek
1. Follow a Proper Acclimatisation Itinerary
The standard EBC trek itinerary is specifically designed around acclimatisation. The key rest days are at Namche Bazaar (3,440m) and Dingboche (4,410m). These rest days are not optional extras — they are essential for allowing your body to adapt.
On acclimatisation days, the “climb high, sleep low” approach is used: you hike to a higher point during the day (e.g., from Namche up to Everest View Hotel at 3,962m) and return to your lower sleeping altitude. This stimulates red blood cell production without the added stress of sleeping at the higher elevation.
2. Ascend Slowly
The general guideline above 3,000m is to increase your sleeping altitude by no more than 300–500m per day. The standard 12–14 day EBC itinerary respects this guideline. Compressed 10-day itineraries skip acclimatisation days and significantly increase AMS risk — avoid them.
3. Stay Hydrated
Dehydration worsens AMS symptoms. Aim to drink 3–4 litres of water per day throughout the trek, even if you don’t feel thirsty. Your urine should be pale yellow. Avoid alcohol above 3,500m — it disrupts sleep and exacerbates altitude symptoms.
4. Pace Yourself on the Trail
Move at a steady, controlled pace — the Nepali phrase is “bistari bistari” (slowly, slowly). You should be able to hold a conversation while walking. If you’re gasping for breath, you’re moving too fast. Many altitude problems on the EBC trek come from trekkers pushing too hard to keep up with faster walkers in the group.
5. Eat Regularly
Altitude suppresses appetite, but your body needs calories to keep warm and maintain energy for trekking. Eat regular meals even if you don’t feel hungry. Carbohydrate-rich foods (dal bhat, porridge, bread, pasta) are good options at altitude.
Diamox (Acetazolamide) for Altitude Sickness
Diamox (acetazolamide) is a prescription medication that can both prevent and treat mild AMS. It works by stimulating faster and deeper breathing, which helps your body take in more oxygen at altitude.
Common preventative dose: 125mg twice daily, starting 1–2 days before ascending above 3,000m and continuing throughout the ascent. The standard treatment dose for developed AMS is 250mg twice daily.
Side effects of Diamox include increased urination, tingling in the hands and feet, altered taste of carbonated drinks, and occasional drowsiness. These are typically mild and manageable.
Important notes on Diamox:
- Diamox is a sulfa drug. People with sulfa allergies should not take it — consult a doctor before using.
- It is not a substitute for proper acclimatisation. It helps your body adapt but does not prevent altitude illness if you ascend too quickly.
- It requires a prescription in most countries. Consult a travel medicine doctor or GP before your trek.
- Diamox is available over the counter at pharmacies in Kathmandu and Namche Bazaar if you haven’t sourced it before the trek.
When to Descend
Descent is the most effective treatment for altitude sickness. Even descending 300–500m can dramatically relieve symptoms. Never delay descent if any of the following are present:
- Symptoms of HACE: confusion, loss of coordination, altered consciousness
- Symptoms of HAPE: shortness of breath at rest, gurgling cough, extreme fatigue
- AMS symptoms that are worsening despite rest at the same altitude
Descend immediately, regardless of time of day or weather. Waiting until morning with HACE or HAPE can be fatal. A minimum descent of 300–500m is usually sufficient to stabilise the patient, who can then continue to a lower medical facility.
Medical Facilities and Helicopter Evacuation
Medical facilities on the EBC route include:
- Himalayan Rescue Association (HRA) Clinic, Namche Bazaar (3,440m) — staffed by volunteer doctors, offers altitude sickness consultation and education talks
- HRA Clinic, Pheriche (4,240m) — another HRA post with volunteer medical staff during trekking season; daily evening talks on altitude sickness
If emergency evacuation is required, helicopter rescue is available from most points on the EBC route. This is expensive (USD $3,000–$6,000+) without insurance. Travel insurance with helicopter evacuation cover to at least 5,500m is essential before attempting the EBC trek.
Your guide or teahouse owner can contact helicopter companies in Kathmandu directly if needed. Emergency numbers are posted at HRA clinics and major teahouses.
The Gamow Bag
A Gamow bag (portable hyperbaric chamber) is sometimes available at HRA clinics and from some trekking companies. It is an inflatable bag into which the affected trekker is placed and pumped to simulate a lower altitude environment. This is a temporary measure — it can stabilise a patient for emergency descent but is not a replacement for actual descent.
Frequently Asked Questions
Will I definitely get altitude sickness on the EBC trek?
Not necessarily. Many trekkers experience only mild symptoms — a slight headache or reduced appetite on the first day at a new altitude — which resolve quickly with rest. Following a proper acclimatisation schedule, staying hydrated, and moving slowly significantly reduces the risk of developing serious AMS.
Can I tell in advance if I’m susceptible to altitude sickness?
There is no reliable way to predict individual susceptibility. Fitness level, age, and previous altitude experience have no consistent correlation with AMS. Even very fit, experienced trekkers can develop altitude illness if they ascend too fast. The only genuine predictor is whether you’ve had AMS before at a given altitude — if you have, you’re more likely to again.
Is it safe to take sleeping pills at altitude?
Sleeping medications (such as benzodiazepines) are generally not recommended at altitude as they can suppress breathing and worsen hypoxia. If sleep is very disrupted, low-dose Diamox taken at night (62.5mg or 125mg) can help by reducing the periodic breathing patterns that disrupt sleep at altitude.
What should I do if I develop a headache at altitude?
Stop ascending. Rest at your current altitude, drink water, and take ibuprofen or paracetamol for the headache. Monitor your symptoms carefully. If the headache worsens or is accompanied by other symptoms (confusion, loss of coordination, difficulty breathing at rest), treat this as a medical emergency and descend.
Do I need to attend the HRA clinic talk?
The HRA clinics at Namche Bazaar and Pheriche run free evening altitude sickness education talks during trekking season. These are highly recommended — they are given by experienced altitude medicine specialists and cover symptoms, prevention, and emergency response in practical, accessible terms. Even experienced trekkers benefit from attending.
Trek Safely with Expert Guidance
Our guides at Everest Trekking Company are trained in wilderness first aid and high-altitude first response. They monitor every trekker for signs of altitude illness throughout the trek and will make safety-first decisions if symptoms develop. We carry basic medical supplies including pulse oximeters to monitor blood oxygen saturation throughout the trek.
View our Everest Base Camp Trek to learn more about how we manage safety on the trail, or contact us with any questions about altitude preparation before your trip.
