Travel guide · Nepal
Altitude Sickness in Nepal
The single most important health topic for trekkers in Nepal — how to acclimatise, spot the warning signs, and know when to turn back.
Altitude sickness is the most important health risk on Nepal's high treks, and the good news is that it is largely preventable with a slow ascent and attention to symptoms. It happens because there is less oxygen in the air as you climb, and your body needs time to adapt. Anyone going above roughly 3,000 m can be affected, regardless of age, fitness or experience. This is general guidance only — speak to a doctor or travel clinic for advice tailored to you. For planning your route, start with our Nepal trekking guide.
What is altitude sickness?
As you gain altitude, air pressure drops and each breath delivers less oxygen. Your body responds by breathing faster and producing more red blood cells, but this adjustment takes days. Climb faster than your body can adapt and you risk altitude sickness. It has nothing to do with being unfit — strong, young trekkers are affected just as often, which is why a careful schedule matters more than training.
The three forms: AMS, HAPE and HACE
- AMS (acute mountain sickness) is the common, mild form. It feels like a hangover — headache, nausea, poor appetite, dizziness and broken sleep.
- HAPE (high-altitude pulmonary oedema) is fluid in the lungs. Signs include breathlessness at rest, a persistent cough and a tight chest. It is a medical emergency.
- HACE (high-altitude cerebral oedema) is fluid on the brain. Signs include confusion, severe headache, loss of coordination and an unsteady, drunken walk. It is also a medical emergency.
AMS is uncomfortable but usually safe if you stop ascending. HAPE and HACE can be fatal within hours, so worsening symptoms always mean descend immediately.
The golden rules of acclimatisation
- Ascend slowly. Above 3,000 m, increase your sleeping altitude by no more than about 300–500 m per day.
- Climb high, sleep low. Day-hike to a higher point, then return to a lower altitude to sleep.
- Take acclimatisation days. Build in rest days every 1,000 m or so to let your body catch up.
- Never ascend with symptoms. If you feel unwell, stay put until you recover.
- Descend if symptoms worsen. Going down even a few hundred metres can bring rapid relief.
- Hydrate and avoid alcohol. Drink plenty of water and skip alcohol and sleeping pills.
Diamox and other medication
Diamox (acetazolamide) is a prescription drug that helps your body acclimatise faster and can reduce the risk and severity of AMS. It is a useful aid, not a licence to climb quickly, and it does not mask dangerous symptoms. Common side effects include tingling in the hands and feet, frequent urination and flat-tasting fizzy drinks. Discuss it with a doctor before you travel — see our notes on health and vaccinations for wider trip-health planning.
Warning signs — and when to descend
Stop and rest if you have a headache, nausea or fatigue. Descend without delay if you notice any of these:
- Breathlessness while resting, or a wet, persistent cough (possible HAPE)
- Confusion, severe headache or an unsteady, staggering walk (possible HACE)
- Mild symptoms that keep getting worse despite rest
The golden rule bears repeating: if you feel bad, do not go higher; if you feel worse, go down. Make sure your Nepal travel insurance covers high-altitude trekking and helicopter evacuation, which can be life-saving in a serious case. For broader peace of mind, our is Nepal safe guide covers other trekking risks.
Which Nepal treks reach high altitude
Most of Nepal's iconic routes spend time at altitude. Everest Base Camp sits at around 5,364 m, with the viewpoint at Kala Patthar reaching about 5,545 m, while the nearby Gokyo Lakes route climbs to similar heights. The Annapurna Circuit crosses the Thorong La pass at roughly 5,416 m, and Annapurna Base Camp tops out near 4,130 m. Choose an itinerary with proper acclimatisation days built in — compare options in our best treks in Nepal guide, and never let a fixed schedule pressure you into ascending while unwell.
Frequently asked questions
At what altitude does altitude sickness start?+
Altitude sickness can begin from around 2,500 m, and the risk rises sharply above 3,000 m where the air holds much less oxygen. Many of Nepal's popular treks spend days above this height, so almost any trekker can be affected regardless of age or fitness. Susceptibility varies from person to person, so it is impossible to predict in advance who will struggle.
What are the symptoms of AMS?+
Acute mountain sickness usually feels like a bad hangover: headache, nausea, loss of appetite, dizziness, fatigue and trouble sleeping. These mild symptoms are common and often manageable with rest, but they are a clear warning to stop ascending. If symptoms worsen or you develop breathlessness at rest or confusion, treat it as an emergency and descend.
How do I prevent altitude sickness in Nepal?+
The best prevention is a slow, steady ascent that gives your body time to acclimatise, ideally gaining no more than 300–500 m of sleeping altitude per day above 3,000 m and taking regular rest days. Stay well hydrated, avoid alcohol and sleeping pills, and never push higher while you have symptoms. A sensible itinerary built into your trek matters far more than fitness.
Should I take Diamox (acetazolamide)?+
Diamox (acetazolamide) is widely used to help speed acclimatisation and reduce the chance of AMS, but it is a prescription medicine and is not a substitute for ascending slowly. Some people experience side effects such as tingling fingers, increased urination or an altered sense of taste. Talk to a doctor or travel clinic before your trip to decide whether it is right for you and at what dose.
What is the golden rule of altitude sickness?+
The golden rule is simple: if you feel unwell, do not go higher, and if you are getting worse, go down. Mild symptoms mean stop and rest at your current altitude until they pass, while worsening symptoms mean descend immediately. Descent is the single most reliable treatment for altitude sickness.
Does the Everest Base Camp or Annapurna Circuit cause altitude sickness?+
Both are high-altitude treks that regularly trigger altitude sickness, since the Everest Base Camp route reaches around 5,545 m at Kala Patthar and the Annapurna Circuit crosses Thorong La at about 5,416 m. Reputable itineraries build in acclimatisation days precisely because so many trekkers feel the effects. With a sensible schedule and attention to symptoms, most people complete them safely.
