Help Prevent Acute Mountain Sickness (AMS)

When the altitude increases, pressure also increases, and oxygen becomes depleted. The human body is capable of adapting to these conditions by increasing its ventilation and heart rate. This initial adjustment usually lasts a few days and requires a significant amount of energy. After about one week, the body will produce more red blood cells to compensate for the lack of oxygen.

If you ascend too quickly above 2,500 metres in altitude, your body can experience considerable stress and begin exhibiting several unpleasant symptoms after a few hours including:
  • Headaches
  • Nausea / vomiting
  • Insomnia
  • Lightheadedness
  • Tiredness
  • Urination decrease
  • Irritability (children)
In some cases, AMS can lead to more serious consequences like:
  • Pulmonary edema
  • Cerebral edema

How to help prevent acute mountain sickness

  • Prevention aims at adjusting the speed of ascent to allow for acclimatization.
  • Plan for a graded ascent
  • Try to avoid rapid ascent to where you’ll be sleeping at altitudes above 3,000 m (9,840 ft)
  • It is recommended to spend 2 to 3 nights at 2,500 m to 3,000 m before going higher
  • Once you have reached 2,500 m to 3,000 m, do not exceed 300-400 metres of ascent per day
  • Allow for one night of acclimatization for each additional 600 to 900 metres of ascent
  • Remain 2-3 consecutive nights at the same altitude every 3-4 days
  • Avoid the use of alcohol and sedatives
  • Do not exert yourself needlessly
  • Prior physical training is a positive aspect, but does not prevent AMS
  • Adjustment to hypoxia is determined by each person’s genetic predisposition (a 20 years old athlete may have a harder time than someone who is 60 years old).
  • In some cases, medication may be prescribed to prevent or treat symptoms
What to do in the event of AMS Symptoms may appear in a few hours when the ascent is very fast, or the acclimatization time is too short. If the following symptoms occur:
  • Headaches
  • Nausea / vomiting
  • Insomnia
  • Lightheadedness
  • Tiredness
You need to:
  • Immediately stop the ascent and wait for the symptoms to disappear
  • If symptoms persist, you need to descend to a lower altitude to help resolution of primary symptoms
  • Certain prescription drugs can be taken to help alleviate symptoms

When things take a turn for the worse…

If these symptoms do not go away and/or worsen:
  • Shortness of breath at rest
  • Cough
  • Fatigue
  • Feeling of chest congestion etc.

Treatment may include:

  • Descending IMMEDIATELY, if possible
  • Administering oxygen, if available
  • Use of certain prescription medications
  • A hyperbaric chamber (if available)

NOTE: If none of these options are available, THE PERSON MUST BE EVACUATED.

*IMPORTANT* When symptoms of altitude sickness appear do not underestimate the symptoms, even minor ones, and do not ascend any higher. If possible, descend. It is important to quickly recognize mountain sickness given the possible progression to cerebral and /or pulmonary edema.

Source: Public Health Agency of Canada (
Source: Centers for Disease Control and Prevention (
Source: Guide d’intervention santé-voyage
Source: Government of Canada:
Source: International Society for Mountain Medecine:
Source: The High Altitude Medecine Guide:

The information provided is for personal use, reference and education only and is not intended to be a substitute for a Physician’s advice, diagnosis or treatment. Please consult your healthcare professional for specific information on personal health matters.