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Travelling at altitude

The Exeter Travel Clinic will help you stay safe in the mountains

Acute Mountain Sickness (AMS)

When people travel to altitudes above 3,000 metres there is a chance they will feel a range of symptoms as a result in the change in air pressure. They include shortness of breath, dizziness, headache and difficulty sleeping, and as a group, are defined as Acute Mountain Sickness (AMS)

These symptoms develop during the first 6 – 12 hours after ascending to and above 3000m and normally resolve over a few days with rest and rehydration. 

Acclimatisation to altitude

The quickest way to suffer from AMS is to ascend too quickly.  Above 3,000m the speed of ascent should be gradual, with the sleeping altitude no higher than 500m from the previous night, with a rest every third day. However, this is not always possible on some trekking routes.

Who gets acute mountain sickness?

Individuals acclimatise at different rates and unfortunately those who have developed altitude sickness previously are more likely to have problems again. Over-exertion and dehydration increase the likelihood of it occurring. Individuals who try and race up a mountain, walking at a pace where they are unable to have a conversation, or do not drink sufficient quantities of water, are more likely to develop the illness. Fitness is a poor indicator as to who may suffer from altitude sickness.

How bad can it get? 

High Altitude Cerebral and Pulmonary Oedema (HACE and HAPE) are two conditions that are potentially fatal. These can occur if individuals continue to ascend before the symptoms of AMS improve. 

Can I do anything to prevent these conditions?

  1. Do not ascend too quickly and take regular breaks
  2. Walk at a pace where you can have a conversation
  3. Stay hydrated (remember you may loose more fluid at altitude)
  4. Get fit for travel. Whilst being unfit does not directly cause AMS, being fitter reduces tiredness 
  5. Consider taking acetazolomide (Diamox)

Diamox tablets 

The human respiratory rate is driven by the amount of carbon dioxide and oxygen in our blood. The levels of these chemicals alter blood acidity, telling our brain to breath faster or slower. At night, whilst sleeping at altitude, our breathing slows down. Diamox (acetazolamide) is a drug that changes the acidity of our blood, tricking the brain into making you breath normally again. It has been used to prevent and treat AMS for over 35 years.

When should I take Diamox?

Diamox should be considered in the following circumstances:

  • Hiking above 4000m
  • When sleeping altitudes above 3000m are more than 500m
  • Rapid ascent to altitude

Common treks we normally consider diamox for are:

  • Kilimanjaro (Africa)
  • Everest Base Camp (Nepal)
  • Mt. Elbrus

Treks where Diamox is not normally required:

  • The Inca Trail (Peru)
  • Mont Blanc (France)
  • Mt. Kinabalu (Borneo)
  • Mt. Toukbal (Morocco)

More information about travelling at altitude can be found here: