Altitude Sickness

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Altitude Sickness Tablets | Diamox

You can order Diamox for altitude sickness online with our UK registered online doctor. Whether it is the Inca trail in Peru, Everest base camp in the Himalayas, (or even Everest itself!), altitude sickness can be a problem. At Simple Online Pharmacy, you can buy Diamox (acetazolamide), without a prescription, since we do this for you.

Acetazolamide alters the acidity of the blood to improve breathing and reduce fluid around the brain and in the lungs. It is this fluid which can sometimes lead to the very severe effects of altitude sickness. Short courses of acetazolamide generally do not cause side effects and stopping the tablets does not cause a rebound in symptoms.

Once you have completed the online doctor consultation, our doctor will review your assessment and prescribe the selected medication if it is approproate. Our pharmacy will then dispense and dispatch your prescription to your door.

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What is Altitude Sickness?

Altitude sickness is the term for conditions that people travelling to high or extreme altitudes may suffer from. The faster the rate of ascent and the higher a person ascends, the more likely they are to suffer from altitude sickness.

Altitude sickness can range from mild, unpleasant symptoms to a potentially fatal condition that rapidly progresses.

Altitude sickness has three forms:

  • Acute mountain sickness (AMS)
  • High altitude pulmonary oedema (HAPE or HAPO)
  • High altitude cerebral oedema (HACE or HACO)

AMS is the milder form while the other two are medical emergencies that can be fatal. The most common cause of death from altitude sickness is from HAPE.

Age, sex or physical fitness does not affect the likelihood of suffering from altitude sickness. This means that the risk of developing altitude sickness is the same for people of all fitness levels. Any pre-existing conditions should be discussed with a medical professional before going to high altitude because some conditions may increase the chances of getting altitude sickness (like congenital heart disease) and other conditions may worsen in high altitudes. 



Altitude sickness occurs when people travel to high altitudes too quickly. High altitudes are described by the NHS as being 2400m + above sea level, this figure can differ slightly between different sources but altitude starts to have an effect on the body around 1500m-2000m above sea level. Scientists are uncertain how exactly altitude sickness occurs but the below information offers some insight and highlights the importance of allowing the body to acclimatize to a new altitude.

As altitude increases, air pressure (barometric pressure) decreases, and oxygen levels also decrease. This decrease in pressure leads to the lungs intaking less oxygen with every breath. This means there is less oxygen available for our body to use for basic functions that keep us alive. 

Our body combats this reduction in oxygen by acclimatising to the new altitude. It does this firstly by making the lungs breathe faster and deeper to increase the amount of air, and therefore oxygen, we intake.

Another important way the body acclimatizes is by increasing the amount of haemoglobin in the blood. Haemoglobin is the carrier of oxygen in our red blood cells. By increasing the amount of haemoglobin in the blood, the amount of oxygen the blood can carry increases. 

This increase in haemoglobin is not as rapid as the breathing changes and happens over a period of days, weeks and months. The body also acclimatizes in other ways, for example by increasing our heart rate.

By climbing to high altitudes too quickly the body has less time to acclimatize. Altitude sickness happens if the body fails to, or does not have enough time to, acclimatize to the new altitude. 



Prevention of altitude sickness is always better than treatment. The key to preventing altitude sickness is to have a gradual ascent with plenty of rest days (days of staying at the same altitude). Any altitudes above 2500m should be travelled to slowly. Below are other preventive measures that should be taken:

  • Choose a trip that allocates time for acclimatization in the itinerary
  • Maintain an adequate intake of fluids
  • Avoid flying directly to areas of high altitude, especially if coming from areas of low altitude
  • Avoid smoking and drinking alcohol at high altitudes
  • When reaching high altitude, avoid taxing exercise for the first day
  • Avoid climbing more than 500m a day
  • Rest every 3 to 4 days or every 600m - 900m ascended

This NHS information from Fit To Travel site has more information and a very useful table to show how many metres people should ascend per day.

Acetazolamide (Diamox)

Acetazolamide is a drug that is used in the prevention and treatment of AMS. There is strong evidence that it reduces the symptoms of AMS in people travelling to high altitude. 

It is unclear how exactly acetazolamide helps to prevent AMS but research has shown that it increases the acidity of the blood (blood acidity is initially decreased at higher altitudes) which helps the body acclimatize. Research has also concluded that acetazolamide is effective in improving periodic breathing during sleep, which is a common problem at high altitude.

The dose can vary but generally, one tablet is taken between 1-4 times a day. It should be taken one to two days before ascent and continued for 48 hours after reaching the highest altitude.

For some people, it may be worth taking one or two doses of acetazolamide before travelling to see how you respond to it. This can help check for side effects such as pins and needles, changing the taste of food and drinks and increasing how often you urinate.


If you think you have AMS (use the Lake Louise Score to help diagnosis) listed below are important actions to take. If you are unsure whether you have AMS or not, if you have recently ascended to a high altitude and have symptoms, assume that you have.

  • Stop and rest where you are
  • Do not go any higher for 24 - 48 hours
  • Take ibuprofen or paracetamol for a headache
  • Anti-sickness medication such as promethazine can be used for nausea
  • Drink enough water (but do not over-hydrate)
  • Do not exercise or exert yourself physically

This is the advice provided on the NHS website. 

Symptoms should gradually improve as your body acclimatizes to the new altitude. If your symptoms do not improve or worsen after 24 hours, it is important to descend at least 500m.

Both HAPE and HACE are medical emergencies. People who develop these conditions need to be immediately carried to a lower altitude and medical attention sought. There are drug treatments that can help treat these conditions if both or either develop, the medical personnel on the trip should carry these.


Symptoms of altitude sickness


Symptoms of AMS do not start immediately when arriving at high altitude. Symptoms generally start after 4-6 hours but may start up to 36 hours after arrival. Symptoms more commonly occur >2500m above sea level but some people may have symptoms at lower altitudes. 

Symptoms are said to be similar to a hangover. These symptoms include:

  • Nausea or vomiting
  • Loss of appetite
  • Headache
  • Dizziness
  • Fatigue
  • Problems sleeping

A useful tool exists for diagnosing AMS called the Lake Louise Score. This can be used to give a score based on various symptoms. A person is diagnosed as having AMS if they have ascended in altitude recently and have a score of 3 or more.


HACE is the more severe form of AMS and is caused by swelling of the brain (cerebral oedema). This is a medical emergency and someone suffering from HACE should immediately descend to lower altitudes, ideally by being carried or transported.

Symptoms of HACE:

  • Becoming confused and/or irrational
  • Severe headache
  • Vomiting
  • Drowsiness
  • Becoming unsteady or unable to walk in a straight line


HAPE is when altitude sickness affects the respiratory system and causes fluid build up in the lungs. This is also a medical emergency requiring immediate descent.

Symptoms of HAPE:

  • Shortness of breath
  • The breathlessness progresses and eventually, the person will be breathless even at rest
  • Persistent coughing (phlegm may be frothy and white or pink)
  • Severe fatigue
  • Blue-tinged skin and/or lips (cyanosis)

HACE and HAPE can often occur together. There are some immediate treatments that can be administered by medical professionals on expeditions but it is always better to prevent altitude sickness rather than try to treat it. If someone shows signs of altitude sickness the best treatment is to descend to a lower altitude.

Periodic breathing and sleep at altitude

A common problem for people at high altitude locations is disturbed sleep. This is called high altitude periodic breathing. Periodic breathing is a cycle of breathing, in which a sleeping person will take deep breaths for a period, followed by a period of much shallower breaths or even pauses in breathing. These pauses can reduce the quality of sleep or cause people to abruptly wake up often. 

As well as periodic breathing, sleeping at altitude can reduce the deeper stages of sleep. For these reasons, people at altitude may find that they often wake up in the night or wake up in the morning not feeling well-rested.


Frequently asked questions  

What else should be considered before travelling to high altitude?

Sun exposure, low temperatures and what types of food and drink to take are just some of the other factors that need to be considered before travelling to high altitude. The MedEx website has an informative booklet that is worth reading before travelling.

Who is prone to altitude sickness?

Anyone, regardless of physical fitness, can suffer from altitude sickness. If a person has suffered from altitude sickness previously, they may be more prone to suffer from it again.

Can altitude sickness kill you?

Altitude sickness can be a life-threatening condition and HAPE or HACE must be treated as medical emergencies. AMS is common at high altitudes but if the correct precautions are taken, most people will have mild symptoms.



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