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Altitude Sickness

Information, advice and help for altitude sickness and forced acclimatisation

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Dr Hilary Jones discusses altitude sickness and the treatments available at HealthExpress

Altitude sickness (also known as acute mountain sickness) occurs when the body finds it difficult to cope with the "thinner air" that is present at high altitudes. Symptoms that can indicate altitude sickness are nausea, tiredness and shortness of breath. The condition can become extremely serious, with the severity of symptoms escalating as altitude is increased. The term high altitude usually refers to heights beginning from 1,500m (5000 ft) above sea level. It is important to take the required precautions in order to help prevent altitude sickness.

Fortunately there is available medication that can help with recovering from symptoms of altitude sickness, if you want to purchase the treatment as a precaution for a future date you can do so below by filling out our online consultation. Alternatively, you can read more about acclimatisation, high altitudes and its effects on the body.

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What is altitude sickness?

In simple terms, altitude sickness is your body's response to the changes in air pressure that are experienced the higher you get from sea level. It is more likely to occur if you ascend too quickly and do not take the necessary precautions while ascending, such as taking the time to acclimatise to the change in height.

The most common form of the condition is acute mountain sickness (AMS). Severe forms of altitude sickness, known as high-altitude pulmonary oedema (HAPO, also known as HAPE) and high-altitude cerebral oedema (HACO, also known as HACE), can be extremely dangerous.[1]

Types of altitude sickness

Acute mountain sickness (AMS)

Most people remain unnoticeably affected at altitudes up to roughly 2500m (8000ft) from sea level. This is around equivalent to the pressure in which airplanes are pressurised. Above this altitude, symptoms may begin to appear. It is easier to prevent AMS rather than treat it. Climbing slowly, and allowing your body to acclimatise naturally significantly lowers your chances of experiencing symptoms. Should you wish to climb at a more rapid pace, it is essential you have the right training and medical help at hand.

Acute mountain sickness is not fatal – although there are two potentially fatal forms of altitude sickness, which are discussed below. AMS may potentially develop into high altitude cerebral oedema (HACO) if not treated properly in time.

High altitude pulmonary oedema (HAPO)

Usually occurring after several days at above 2500m (8000ft) – HAPO occurs when fluid collects in the lungs as a result of high altitude, meaning the person becomes increasingly starved of sufficient oxygen to operate at a functional level. For this reason, it can become fatal within hours. There is insufficient evidence to predict who will get it or why, and there is also a lack of research into how the fluid exactly gets into the lungs.

The best way to alleviate the symptoms of HAPO is to descend, provide additional oxygen and raising the air pressure around the sufferer. Sometimes a medical professional will use a medicine such as dexamethasone. To prevent HAPO from occurring, it is essential the person has acclimatised properly before moving or remaining in such high altitudes.[2]

High altitude cerebral oedema (HACO)

Similar to HAPO, HACO involves internal fluids – although in this condition it involves fluid in the brain. High altitude cerebral oedema can prove fatal within a few hours, and induces a coma before that. Symptoms include severe headaches, confusion, vomiting and an inability to walk 'heel-to-toe' in a straight line.

Around 1% of people who ascend above 3000m develop this condition, and it usually occurs in people who ignore early acute mountain sickness symptoms and continue to climb at a fast rate.

The main treatment of this condition is descent. Additional treatment of HACO may include dexamethasone medicine, a Gamow bag and a portable hyperbaric altitude chamber.

What is acclimitisation?

To best prepare for climbing high altitudes, or to prevent the above types of altitude sickness, it is recommended for the person to acclimatise properly so that their body becomes accustomed to the higher altitudes, thereby preventing the risk of adverse health effects.

The guideline below shows the steps to take when acclimatising:

  • Ensure you have no prior cardiovascular ailments that would prevent progression in higher altitudes
  • Those with asthma or COPD may be advised against going past a certain altitude
  • When ascending, ensure you do so with regular overnight stops
  • Those planning to climb over 3,000 meters (10,000 feet) should make sure they spend a night just below 3,000 meters before beginning their ascension.
  • When ascending, this should only be done at a pace of between 250-500 meters (800-1,500 feet) per day with a sleep interval required before attempting the new height.
  • Every 1,000 meters (3,000 feet) climbed will require a full 2 nights sleep before further ascension

What are the causes of altitude sickness?

When you ascend to high altitudes, the air pressure becomes lower than it is at and near sea level. This means that the air is thinner and you are not able to breathe in the same amount of oxygen as before, meaning there is less oxygen reaching your bloodstream. Your body responds to this by increasing your pulse rate and your breathing to ensure an adequate supply of oxygen is supplied throughout your body. The decreased intake of oxygen also causes changes in the acidity of your blood, a disturbance to the balance of electrolytes or fluid and increased pressure in lung circulation.

  • high altitudes Thinner air at high altitudes
  • oxygen intake Decreased oxygen intake
  • balance of electrolytes Disturbance to the balance of electrolytes
  • pressure on the lungs Increased pressure on the lungs

What are the symptoms of altitude sickness?

The first symptoms are usually noticeable about six hours after you have reached a point of high altitude. Common symptoms include:

  • symptomsNausea
  • symptomsTiredness
  • symptomsShortness of breath
  • symptomsHeadache
  • symptomsUnsteadiness
  • symptomsDiarrhoea

More severe acute altitude sickness can result in chest pain and vomiting, in addition to the aforementioned symptoms.

Myths about altitude sickness

1) "I'm really fit, I won't get altitude sickness"

Being physically fit does not make one immune from altitude sickness. It doesn't matter whether you're very sedentary, or an athlete, it doesn't alter the way your body reacts. Age does seem to make a difference, with the over 50s having a slightly lower risk.

Moreover, more and more young people are visiting places such as Machu Picchu near Quinto, Peru – a place relatively well known for it's height above sea level. However, compared to some of the skiing resorts in the Alps, it is only a relatively tame 8000ft, meaning that most people who attend don't need to worry anyway, provided they take their time on the way up.

2) "It's the same as vertigo"

Altitude sickness and vertigo are two unrelated conditions. Altitude sickness occurs due to a physiological reaction in the body in response to increased altitude and/or rapid ascent. Vertigo refers to the feeling of yourself or the environment around you spinning or moving. It is often confused with acrophobia, which is a fear of heights – which can produce feelings of dizziness, nausea and panic. Vertigo, whilst similar, is also a separate condition to motion sickness.

3) "You can't get it in a plane"

One of the more common misconceptions about altitude sickness is that it is solely the preserve of climbers and Kilimanjaro mountaineers. A study by the New England Journal of Medicine showed that although a small number, even some aeroplane passengers suffer from altitude sickness – albeit mild symptoms. This is because planes are often pressured at around 2500m (8000ft), and at that altitude, people more sensitive to this condition may experience some symptoms.

What are the benefits of treating altitude sickness?

Certain forms of altitude sickness can potentially be fatal, so it's really important to keep it under control by using prevention techniques or treatment. You may also be on a skiing trip or mountain climbing, for example, so treating your ailment also ensures you can continue your holiday without having to worry about dealing with altitude or acute mountain sickness.

  • Prevent potential fatal effects
  • Reduce risk of associated symptoms

How can I treat altitude sickness?

There are treatments you can take to help prevent altitude sickness symptoms occurring, such as herbal medicines and prescription medications like Diamox, which contain acetazolamide. It is important to note that no medication is a substitute for acclimatisation, and it is essential to follow the appropriate steps when ascending to high altitudes.

Herbal remedy for altitude sickness

Noted herbal supplements for the treatment of sickness at high altitude include ginkgo biloba extract. Whilst some reports say that these can help with certain symptoms – there is inconclusive evidence that these herbal remedies are as effective as prescription medication for altitude sickness.

Prescription treatments:

Diamox (Acetazolamide) is a treatment we provide, which is clinically proven to prevent sickness at high altitudes and is approved by UK registered doctors. It is recommended that you follow these dosage guidelines when using Acetazolamide:

  • One day before ascent: take 125 mg twice a day
  • Day of ascent: take 125 mg twice a day
  • One to two days after: take 125 mg twice a day

All these types of treatment are suitable for the first and non-fatal kind of altitude sickness (AMS), the more severe forms of HACO/HAPO require serious assistance from a doctor or someone highly experienced in altitude emergencies.

Preventing altitude sickness

It is extremely important to be completely prepared when ascending to high altitudes, as failing to do so will put you at risk of experiencing extremely serious consequences. You should bear in mind that anyone is at risk of altitude sickness, even those people who are very fit and have ascended to high altitude before. It is important to ascend slowly, over several days, taking the time to acclimatise to higher altitudes. You should eat foods high in carbohydrates and drink plenty of fluids.

If you know you're going on a trip where you know you might experience higher altitudes – such as climbing Kilimanjaro – make sure you take the necessary precautions to avoid potentially fatal altitude sickness. It's also important to remember that just because you haven't experienced altitude sickness symptoms on one trip, that you won't experience them on another.

Guidelines to follow:

  1. If you're feeling ill, then you have altitude sickness until proven otherwise
  2. Don't climb to a further height if you experience any altitude sickness symptoms
  3. If you feel symptoms increasing – descend to a lower height as soon as if safe

Can anyone be affected by altitude sickness?

Altitude sickness affects all people and it doesn't depend on personal factors such as age, sex or your level of fitness. Certain people are affected, while others are less susceptible to it. Just because you haven't had it before doesn't mean you won't develop it on another trip.

Who should be cautious in high altitudes?

Anyone who has experienced either of the more severe forms of altitude-related illness (HAPO or HACO) should never re-enter such an environment. unless they have been given complete approval by a medical professional.

Pregnant women and children, people with severe diabetes or high blood pressure should always be cautious.[5]

What do HealthExpress offer for altitude sickness?

If you would like to buy a treatment that can help to prevent symptoms of altitude sickness, it is possible to buy Diamox (Acetazolamide) online here at HealthExpress. We ask that you complete an online consultation if you would like to do this, to ensure that the medication will be effective and safe for you to use. A doctor will review your consultation and make a recommendation based on this information. You will then be able to place your order. If you live in London you can benefit from same day delivery, provided you purchase before 4pm.

Why choose HealthExpress?

  • Fast, free delivery - order before 4pm and receive your treatment the next day (same day for London postcodes)
  • Free online consultation service with one of our registered GMC doctors
  • Discreet packaging - we don't include any branding or pharmacy logo on our packaging meaning you can get your treatment delivered anywhere
  • UK based and GMC UK registered
  • Only proven prescription medication available and approved by the National Pharmacy Association and CareQuality Commission
  • All inclusive confidential service


Dr Hilary Jones, HealthExpress Medical Advisor

What to do if you have altitude sickness

Altitude sickness is a very serious condition, however it can be avoided if climbers ensure that they acclimatise properly.In addition to this, extra precautions in the form of prescription treatment are also available.

Click here to find the right treatment for you