About Acute Mountain Sickness (AMS)

The World Health Organization estimates that over 35 million people travel to altitudes of 3,000 metres or above each year. However, there are risks associated with climbing to altitude. Acute mountain sickness (AMS) can be unpleasant and may reduce enjoyment of activities. In addition, if it is not managed appropriately it can result in more serious illness, which can lead to death. An understanding of the prevention and recognition of AMS is important to anyone travelling to high altitude.

Best way to avoid AMS is to put up your feet and enjoy the view as often as possible.

Best way to avoid AMS is to put up your feet and enjoy the view as often as possible.

What is acute mountain sickness?

As you ascend to altitude the air becomes thinner. Due to the lower pressure of the air, there is less oxygen available per breath.  You will notice that you are more readily getting short of breath with increased activity.

This lack of oxygen triggers changes in your body to help it adapt to its new environment. This is what we call “acclimatizing”, which includes breathing faster than usual, and passing urine more frequently.

AMS may be experienced when your body is not properly acclimatized to the altitude.



What are the symptoms of acute mountain sickness?

The main symptom is headache, which is the result of mild swelling of the brain, caused by the reduced oxygen levels. This can vary in severity. Rarely, people can experience more severe swelling leading to a condition called high altitude cerebral edema (HACE).

For a diagnosis of mild mountain sickness to be made you need a headache plus one other symptom from:

  • Difficulty sleeping
  • Dizziness or light-headedness
  • Fatigue
  • Loss of appetite
  • Nausea or vomiting
  • Rapid pulse
  • Shortness of breath with exertion

Symptoms that may occur with more severe mountain sickness include:

  • Blue color to the skin (cyanosis)
  • Chest tightness or congestion
  • Confusion
  • Cough
  • Coughing up blood or frothy pink sputum
  • Altered consciousness
  • Withdrawal from social interaction
  • Gray or pale complexion
  • Inability to walk in a straight line, or to walk at all
  • Shortness of breath at restIf you experience any of these symptoms at altitude and wonder whether you have AMS, you can be scored by your guide to find out.

How is the AMS score calculated?

The Lake Louise score is a scoring system used to make a diagnosis of AMS. This is done to determine how severe your symptoms are and what they mean. The scoring is as follows:


Symptom Severity Score
Headache No headache
Mild headache
Moderate headache
Severe headache
Gastrointestinal symptoms None
Poor appetite or nausea
Moderate nausea and/or vomiting
Severe nausea and/or vomiting
Fatigue and/or weakness Not tired or weak
Mild fatigue/weakness
Moderate fatigue/weakness
Severe fatigue/weakness
Dizziness/light-headedness Not dizzy
Mild dizziness
Moderate dizziness
Severe dizziness
Difficulty sleeping Slept as well as usual
Did not sleep as well as usual
Woke many times, poor sleep
Could not sleep at all

A total score of 3 to 5 = mild AMS and 6 or more = severe AMS. Standard practice is to assume that any symptoms at altitude are altitude illness until proven otherwise.

How can I prevent developing altitude sickness?

The best way to try to prevent altitude sickness is to ascend to higher altitudes slowly. This gives time for your body to acclimatize to the new conditions. Different people will acclimatize at different rates. Remember to keep well hydrated and stay well nourished.

How can I ascend safely?

The following are the recommended rates of ascent to altitude to help with proper acclimatization:

Located at 2,800m above sea level, the 460 metre, 12% slope runway of the Tenzing-Hillary Airport in Lukla has one of the highest and steepest in the world.

Located at 2,800m above sea level, the 460 metre, 12% slope runway of the Tenzing-Hillary Airport in Lukla is one of the highest and steepest in the world.

  • If possible, spend at least one night at an ‘intermediate’ elevation below 3000 metres.  On the Everest Trek, we do not start the trek upon arrival in Lukla; rather, we stay one night and begin the trek the next morning.
  • Above 3000 metres, increase your sleeping altitude by only 300-500 metres per day.  Himalayan Trexplorers’ groups move at a purposely slow rate to ensure compliance with this rule, and routinely stop in villages commonly omitted by other groups (Dughla and Pangboche being notable examples)
  • Above 3000 metres, take a rest day for every 1000 metres of elevation gained (i.e. spend a second night at the same altitude).  On the Everest Trek we have several rest days in Namche Bazzar, Pangboche, Dingboche, and Gorak Shep.
  • If possible, don’t fly or drive directly to high altitude.  Our groups routinely fly to Lukla, but we do not fly higher than this elevation, to allow proper acclimatization.
  • If you do go directly to high altitude by car or plane, do not over-exert yourself or move higher for the first 24 hours.  Himalayan Trexplorers groups make a special point of taking it easy on the first day of trekking, and rarely move on the arrival day in Lukla
  • Always try to sleep at a lower altitude. Climbers commonly use the phrase, “climb high, sleep low”.  We do just that during acclimatization hikes in Namche, Pangboche, Dingboche, and Gorak Shep, when we climb up to nearby viewpoints and ridges.
  • If symptoms are not improving, delay further ascent.  We are not in a rush and all our customers are well informed about the possibility or necessity of an additional rest day.  This is seen as a treat rather than an inconvenience as it allows us to explore more of the surroundings, see more, experience more, and get more out of the trip.
  • If symptoms get worse, move down as soon as possible.  We are fully prepared for the eventuality of an evacuation, whether on foot, or using a helicopter.  This, however is a very rare occurrence as our itineraries are slow enough that even baseline headaches are rare.
  • If evacuation is not possible we have access to a portable hyperbaric chamber which allows hikers to simulate conditions at lower altitudes without actually moving from their location on the mountain. This device (also known as a Gamow Bag) is very helpful if bad weather or other factors make flying or walking down impossible.
  • While trekking at high elevations you should drink plenty of fluids, avoid alcohol, and eat regular meals high in carbohydrates.  You should avoid high altitudes if you have heart or lung disease.

What should I do if I get AMS?

In the unlikely event of the Trexplorers' itinerary being too fast, our helicopter can easily bring you back down to Lukla or Kathmandu, but this is a weather dependent and a relatively pricey option.

In the unlikely event of the Trexplorers’ itinerary being too fast, a helicopter can easily bring you back down to Lukla or Kathmandu, but this is a weather dependent and a relatively pricey option.

If you are suffering with symptoms of AMS, the first step is to rest at the same altitude. Usually symptoms resolve with rest and painkillers (Paracetamol or Ibuprofen) within 24 hours. If symptoms do not resolve or if they get worse, you will descend to the next village down. It is common that even a short descent and rest will improve symptoms significantly. It may still be possible to ascend again if you have recovered and our generous and flexible schedule certainly allows for this.

Once we are near or above 4000 metres we are in contact with the Himalayan Rescue Association’s outposts which make their medical facilities available to trekkers and provide oxygen.  Also, if needed, the HRA has a Gamow Bag which is a recompression tool which allows a person with severe symptoms to be treated and/or evacuated to lower elevation.  Click here for a video of a simulated Gamow Bag experience.



Tell me more about medications to prevent acute mountain sickness.

Acetazolamide (Diamox) can used for the prevention and treatment of acute mountain sickness (AMS).  Readily available for purchase in Kathmandu, acetazolamide speeds up your rate of acclimatization but it does not mask the symptoms of AMS. Acetazolamide does not protect against worsening AMS with continued ascent. The usual dose of acetazolamide for prevention is 125 mg, twice a day. There is good evidence for its effectiveness although there are side effects, most common being increased urine production, which can result in many middle-of-the-night trips to the toilet, as well as somewhat distracting pins and needles in your fingers and toes.  This simply means that you need to drink more water when using Diamox, avoid alcohol, which causes dehydration, and generally take it easy on the trail.

There is some evidence that the steroid dexamethasone can be used to prevent AMS. However, this is not recommended for routine use in travellers to high altitudes.

There is no reliable evidence for any other medications (including gingko biloba) at present. In Nepal, there are many “alternative” herbal remedies offered for the treatment of AMS, but we certainly do not recommend these and in fact advise our customers to steer clear.