Acute Mountain Sickness

Condition 101

What is the definition of Acute Mountain Sickness?

Acute mountain sickness is an illness that can affect mountain climbers, hikers, skiers, or travelers at high altitudes, usually above 8000 feet (2400 meters).

What are the alternative names for Acute Mountain Sickness?

High altitude cerebral edema; Altitude anoxia; Altitude sickness; Mountain sickness; High altitude pulmonary edema

What are the causes for Acute Mountain Sickness?

Acute mountain sickness is caused by reduced air pressure and lower oxygen levels at high altitudes.

The faster you climb to a high altitude, the more likely you will get acute mountain sickness.

The best way to prevent altitude illness is to ascend gradually. It is a good idea to spend a few days ascending to 9850 feet (3000). Above this point ascend very slowly so that the elevation at which you sleep does not increase more than 990 feet to 1640 feet (300m to 500m) per night.

You are at higher risk for acute mountain sickness if:

  • You live at or near sea level and travel to a high altitude.
  • You have had the illness before.
  • You ascend quickly.
  • You have not acclimatized to the altitude.
  • Alcohol or other substances have interfered with acclimatization.
  • You have medical problems involving the heart, nervous system, or lungs.

What are the symptoms for Acute Mountain Sickness?

Your symptoms will also depend on the speed of your climb and how hard you push (exert) yourself. Symptoms range from mild to life-threatening. They can affect the nervous system, lungs, muscles, and heart.

In most cases, symptoms are mild. Symptoms of mild to moderate acute mountain sickness may include:

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

Symptoms that may occur with more severe acute mountain sickness include:

  • Blue color to the skin (cyanosis)
  • Chest tightness or congestion
  • Confusion
  • Cough
  • Coughing up blood
  • Decreased consciousness or withdrawal from social interaction
  • Gray or pale complexion
  • Inability to walk in a straight line, or walk at all
  • Shortness of breath at rest

What are the current treatments for Acute Mountain Sickness?

Early diagnosis is important. Acute mountain sickness is easier to treat in the early stages.

The main treatment for all forms of mountain sickness is to climb down (descend) to a lower altitude as rapidly and safely as possible. You should not continue climbing if you develop symptoms.

Extra oxygen should be given, if available.

People with severe mountain sickness may need to be admitted to a hospital.

A medicine called acetazolamide (Diamox) may be given to help you breathe better. It can help reduce symptoms. This medicine can make you urinate more often. Make sure you drink plenty of fluids and avoid alcohol when taking this drug. This medicine works best when taken before reaching a high altitude.

If you have fluid in your lungs (pulmonary edema), treatment may include:

  • Oxygen
  • A high blood pressure medicine called nifedipine
  • Beta agonist inhalers to open the airways
  • Breathing machine in severe cases
  • Medicine to increase blood flow to the lungs called phosphodiesterase inhibitor (such as sildenafil)

Dexamethasone (Decadron) may help reduce acute mountain sickness symptoms and swelling in the brain (cerebral edema).

Portable hyperbaric chambers allow hikers to simulate conditions at lower altitudes without actually moving from their location on the mountain. These devices are very helpful if bad weather or other factors make climbing down the mountain impossible.

What is the outlook (prognosis) for Acute Mountain Sickness?

Most cases are mild. Symptoms improve quickly when you climb down the mountain to a lower altitude.

Severe cases may result in death due to lung problems (pulmonary edema) or brain swelling (cerebral edema).

In remote locations, emergency evacuation may not be possible, or treatment may be delayed. This can have a negative effect on the outcome.

The outlook depends on the rate of descent once symptoms begin. Some people are more prone to developing altitude-related sickness and may not respond as well.

What are the possible complications for Acute Mountain Sickness?

Complications may include:

  • Coma (unresponsiveness)
  • Fluid in the lungs (pulmonary edema)
  • Swelling of the brain (cerebral edema), which can lead to seizures, mental changes, or permanent damage to the nervous system
  • Death

When should I contact a medical professional for Acute Mountain Sickness?

Call your provider if you have or had symptoms of acute mountain sickness, even if you felt better when you returned to a lower altitude.

Call 911 or your local emergency number if you or another climber have any of the following symptoms:

  • Altered level of alertness
  • Coughing up blood
  • Severe breathing problems

Climb down the mountain right away and as safely as possible.

How do I prevent Acute Mountain Sickness?

Keys to preventing acute mountain sickness include:

  • Climb the mountain gradually. Gradual ascent is the most important factor in preventing acute mountain sickness.
  • Stop for a day or two of rest for every 2000 feet (600 meters) of climb above 8000 feet (2400 meters).
  • Sleep at a lower altitude when possible.
  • Make sure that you have the ability to rapidly descend if needed.
  • Learn how to recognize early symptoms of mountain sickness.

If you are traveling above 9840 feet (3000 meters), you should carry enough oxygen for several days.

If you plan on climbing quickly, or climbing to a high altitude, ask your provider about medicines that may help.

If you are at risk for a low red blood cell count (anemia), ask your provider if your planned trip is safe. Also ask if an iron supplement is right for you. Anemia lowers the amount of oxygen in your blood. This makes you more likely to have mountain sickness.

While climbing:

  • Do not drink alcohol
  • Drink plenty of fluids
  • Eat regular meals that are high in carbohydrates

You should avoid high altitudes if you have heart or lung disease.


Basnyat B, Paterson RD. Travel medicine. In: Auerbach PS, Cushing TA, Harris NS, eds. Auerbach's Wilderness Medicine. 7th ed. Philadelphia, PA: Elsevier; 2017:chap 79.

Harris NS. High-altitude medicine. In: Walls RM, Hockberger RS, Gausche-Hill M, eds. Rosen's Emergency Medicine: Concepts and Clinical Practice. 9th ed. Philadelphia, PA: Elsevier; 2018:chap 136.

Luks AM, Hackett PH. High altitude and preexisting medical conditions. In: Auerbach PS, Cushing TA, Harris NS, eds. Auerbach's Wilderness Medicine. 7th ed. Philadelphia, PA: Elsevier; 2017:chap 3.

Luks AM, Schoene RB, Swenson ER. High altitude. In: Broaddus VC, Mason RJ, Ernst JD, et al, eds. Murray and Nadel's Textbook of Respiratory Medicine. 6th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 77.

Latest Research

Latest Advance
  • Condition: COVID-19
  • Journal: Respiratory physiology & neurobiology
  • Treatment Used: Erythropoietin
  • Number of Patients: 0
  • Published —
The study researched the use of Erythropoietin in treating COVID-19.
Latest Advance
  • Condition: High Altitude Headache and Acute Mountain Sickness
  • Journal: Wilderness & environmental medicine
  • Treatment Used: Metoclopramide and Ibuprofen
  • Number of Patients: 47
  • Published —
The study researched the use of Metoclopramide and Ibuprofen in treating high altitude headache and acute mountain sickness.
Latest Advance
  • Condition: Acute mountain sickness
  • Journal: Medwave
  • Treatment Used: Acetazolamide
  • Number of Patients: 0
  • Published —
The study researched the use of acetazolamide in patients with acute mountain sickness.
Latest Advance
  • Condition: Altitude sickness
  • Journal: The Cochrane database of systematic reviews
  • Treatment Used: Pre-acclimitization, positive end expiratory pressure (PEEP), herbal antioxidnats
  • Number of Patients: 1406
  • Published —
To assess the clinical effectiveness and adverse events of miscellaneous and non-medication interventions for preventing acute HAI in people who are at risk of developing high altitude illness in any setting.

Clinical Trials

Clinical Trial
  • Status: Recruiting
  • Study Type: Drug
  • Participants: 30
  • Start Date: January 14, 2019
Spectroscopic and Diffusion Weighted Analysis of the Effects of Dexamethasone on High Altitude Cerebral Oedema (HACE)
Clinical Trial
  • Status: Recruiting
  • Study Type: Other
  • Participants: 72
  • Start Date: January 1, 2019
Investigation of Physiological Adaptations to Simulated Intermittent Altitude on Human Health and Performance
Clinical Trial
  • Status: Recruiting
  • Participants: 28
  • Start Date: October 1, 2018
Does Patent Foramen Ovale Size Matter in Men and Women
Clinical Trial
  • Status: Recruiting
  • Study Type: Device
  • Participants: 100
  • Start Date: August 9, 2018
Breathing Training to Improve Human Performance at High Altitude