Altitude Sickness

Acute mountain sickness (sometimes known as altitude sickness) is caused by the lack of oxygen at high altitudes. Symptoms start usually above 2700m. This is a hard condition to predict and while usually mild there can be serious complications especially when there are pre-existing medical conditions.

Common destinations for us to offer advice on acute mountain sickness (AMS) include Cuzco, Himalayan treks, Mt Kilimanjaro.
The best treatment is descent to a lower altitude, especially before nightfall.
There are useful medications available.

Risk Factors

Early symptoms include headaches, nausea, breathlessness, palpitations (rapid heartbeats), loss of appetite and reduced ability to exercise. Sleep can also be affected, waking frequently through the night due to ‘periodic’ breathing. Complications can develop, especially with rapid ascent to high altitude, and some may experience severe breathing difficulties. This more severe form is called high altitude pulmonary oedema (HAPE). High altitude cerebral oedema (HACE) is characterised by lack of coordination, confusion, severe headaches and even loss of consciousness. Although uncommon, both HAPE and HACE are potentially fatal.


The best way to avoid altitude sickness is to ascend slowly, taking several days to reach the intended destination. This allows the body time to get used to the decreasing supply of oxygen available at high altitude and is a process called acclimatization. At high altitudes it can take three to five days for your body to acclimatize before you should ascend further. If it is not possible to acclimatize, for example, if you are taking a short flight from sea-level to 3000 meters or more, acclimatization can be helped by taking the medicine acetazolamide, which helps by increasing a person’s breathing rate and increasing oxygen to the tissues. This will reduce the risk of altitude sickness, but won’t guarantee to prevent it. If suffering from altitude related symptoms, it is always advisable to descend. Oxygen, when available, is the best treatment.
It is also important to stay hydrated when at high altitude. Dehydration worsens altitude sickness. Much water is lost through breathing in cold, high altitudes, and also through sweat, especially when undergoing activities such as skiing or trekking. Avoiding strenuous activity in the first 24 hours at high altitude also helps to reduce the symptoms of AMS. Alcohol and sleeping pills slow down the acclimatization process and should be avoided. Alcohol also causes dehydration and worsens AMS.


  • Are there any problems associated with taking acetazolamide?

    Mostly no, but with some caveats;
    Avoid if allergic to sulphur drugs.
    It is a diuretic so dehydration can be a problem - drink plenty of fluids.
    There are potential side effects such as nausea, dizziness and tingling but usually with extended use. Trials prior to travel are often advised especially if on medications for high blood pressure.

  • Will tour operators know the signs and symptoms of AMS?

    Reputable and experienced tour operators should definitely know what to look out for, but if you are travelling with friends and family, make sure they do too. They are best placed to notice a change in your behaviour and its worth having a pre-departure discussion with them about the importance of descent if they appear.

  • Anything else I need to know?

    Don't let peer pressure or the cost of your trip influence your decision to push on if you are experiencing acute mountain sickness. Descend!

  • Are any other medications useful?

    There is some evidence for using ibuprofen, viagra and dexamethasone but these need careful discussion.

Some Affected Locations