Not everyone will climb Everest but if you’re lucky enough to go mountaineering beware of altitude sickness. It happens when you travel above 2500m and your body doesn’t have enough time to adjust to the lower air pressure and oxygen. You might feel headachy, dizzy, sick and have trouble breathing or a racing heart. Gradual ascent, staying hydrated, and avoiding alcohol are key steps. If symptoms persist, medication can provide relief. In severe cases, immediate descent and medical attention might be necessary. Let’s make sure you’re well-prepared for your high-altitude journey.
Don't wait any longer to get the medical help you need. Once you complete a short online assessment about your condition, you will be able to select your preferred treatment and quantity from a list of appropriate options for you.
Take a quick 1-3 minute assessment
Delivered in secure, plain packaging on fully tracked delivery from just £2.95
Our team of doctors and pharmacists, and our support staff, are all UK-based.
Have a question? Telephone support is always free; Monday - Friday, 9am - 5pm.
Based on over 24,000 reviews collected on Google and Reviews.io.
We maintain the highest possible regulation for a UK online pharmacy, ensuring your experience with us is secure, safe, and confidential.
Regulation Info
The CQC ensures we are held to the same regulatory standard as your local GP, as well as dentists, social care, care homes and more.
The GPhC inspects and regulates all pharmacies in the UK. They ensure that our processes & procedures meet the standards you would expect from your local chemist.
Altitude sickness (also known as acute mountain sickness) commonly occurs in climbers that reach a high altitude too quickly without time to adjust to the new environment. As altitude increases the atmospheric pressure decreases, meaning there is decreasing levels of oxygen in the air you breathe. This decrease in the amount of oxygen you are breathing in causes the symptoms of altitude sickness including headache, nausea, dizziness and exhaustion.
Altitude sickness is common amongst climbers and skiers who spend time at 2,500m (8,000 feet) above sea level. Symptoms tend to get more severe at altitudes of 3,600m (12,000 feet) or more. There is no specific demographic that is more likely to develop altitude sickness than others; it is not affected by age, sex, fitness or weight. Some people are more susceptible to getting altitude sickness than others, and it does not mean you will experience it in the future because you have had it previously.
At altitudes of 2,500m (8,000 feet) or higher, the symptoms of altitude sickness can appear within 6 to 24 hours if you have ascended the mountain too quickly.
The symptoms of mild altitude sickness include:
There will usually be a general feeling of being unwell, like having a bad hangover. Normally the symptoms of altitude sickness are worse at night.
In more severe cases of altitude sickness the following symptoms may occur:
In addition to these symptoms, there may be a worsening of the symptoms of mild altitude sickness above. Severe symptoms of altitude sickness can be a sign of cerebral or pulmonary oedema (excess fluid in the skull/lungs) and is a medical emergency. You should descend immediately and seek professional medical treatment.
Altitude sickness is normally self-diagnosed or diagnosed by a peer, based on your symptoms. If there is a medical professional on your trip, they will be able to diagnose altitude sickness and give advice on its treatment.
Before travelling you should always familiarise yourself with the symptoms of Altitude sickness to allow you to quickly recognise them in yourself or others. Fast response and treatment of Altitude Sickness is extremely important to reduce any danger associated with the condition.
Remember: if you experience or suspect severe symptoms of altitude sickness, you should descend with a partner and seek immediate medical treatment.
Halt your ascent or descend up to 500m
If you are experiencing symptoms of mild altitude sickness, do not ascend any further for at least 24 to 48 hours, until your symptoms have cleared. You may wish to descend up to 500m to help ease symptoms and speed up acclimatisation. If the symptoms of mild altitude sickness do not go away after 48 hours you need to descend by at least 500m (1,600 feet) and not climb again until they have completely disappeared.
To aid acclimatisation and ease symptoms of mild altitude sickness:
Always ensure you tell your group how you are feeling so they can be aware to look out for symptoms of severe altitude sickness.
Oxygen treatment can be helpful to ease symptoms of altitude sickness to allow you to descend and acclimatise. Oxygen treatment is not a replacement for descending and acclimatising.
Paracetamol or ibuprofen can be used to treat pain or discomfort from headaches caused by mild altitude sickness.
Promethazine (Phenergan) tablets can be used to treat nausea and sickness associated with mild altitude sickness. Promethazine is an antihistamine that also acts as an anti-emetic (it stops nausea & vomiting).
Diamox (Acetazolamide)
Diamox (acetazolamide) can help to both ease the symptoms of, and prevent mild altitude sickness. It helps to correct the chemical imbalance in your brain caused at high altitudes. Diamox can help to reduce the recovery time from mild altitude sickness from 24-48 hours to 12-24 hours, provided you do not ascend further in this time.
Diamox can also help to prevent altitude sickness in people who are ascending quickly without time to properly acclimatise. There is still, however, the risk of serious altitude sickness if you do not properly acclimatise, which can result in a medical emergency. Rapid ascent is not recommended.
Diamox can occasionally cause mild side effects. These can include slight numbness or tingling in the face, fingers or toes, some loss of appetite, taste disturbance, flushing, thirst, headache, dizziness, fatigue, and irritability. Most doctors suggest taking a trial dose of Diamox for a couple of days before your trip to ensure you do not suffer any adverse reactions (this is normally half a tablet daily for 2-4 days).
Remember, even in those taking Diamox, it is still important to properly acclimatise. You should never ascend further until your symptoms have completely gone and you are properly acclimatized to your current altitude. Do not use Diamox to push through the symptoms of altitude sickness and continue to climb, this is extremely dangerous and can be fatal.
The most effective way to prevent altitude sickness at altitudes of 2,500m and above is proper acclimatisation. Climbing slowly will give your body proper chance to adapt to the changes in oxygen levels at high altitudes.
Rules to follow for proper acclimatisation:
For walking or trekking holidays that involve climbing low peaks or crossing ridges but sleeping in valleys, altitude sickness is unlikely to be a problem. On skiing holidays where you are staying in a valley or sleeping at heights of 3,000m (10,000 feet) or less, altitude sickness is unlikely to be a problem. On climbing holidays where you will ascend to over 3,500m (12,000 feet) such as higher peaks in the Alps, Kilimanjaro and the Colorado Rockies, a few days spent climbing lower peaks to acclimatise is recommended.
Diamox (acetazolamide) can also be taken two days before, during your ascent and for one day after to help prevent altitude sickness.
For further information on proper acclimatisation techniques, see the 'How is Altitude Sickness Treated?' section above.
Alternative measures to take if Acetazolamide is not available:
If you are experiencing symptoms of mild altitude sickness, do not ascend any further for at least 24 to 48 hours, until your symptoms have cleared. You may wish to descend up to 500m to help ease symptoms and speed up acclimatisation.
It’s the inability to get enough oxygen to be able to function properly at high attitude. It is separated into 2 different conditions, mild, and severe altitude sickness.
It occurs when you climb levels higher than 2500m or 8250ft above sea level.
The higher you go up, the lower atmospheric pressure gets. This makes it difficult for you to get the oxygen you need to function properly.
Altitude symptoms present 6 to 24 hours after you start going up in altitude to levels 2500m above sea level.
Symptoms of mild altitude sickness include
If left untreated then they can become worse and develop into severe altitude sickness.
Severe Altitude Sickness is rare but it it's important to be aware of symptoms as they indicate there may be a build-up of fluid in the brain and/or lungs. This can be potentially life threatening.
This is also sometimes referred to as HACE or High Altitude Cerebral Oedema. The lack of oxygen causes the fluid to leak out from the blood vessels and cause swelling around the brain.
It has a tendency to occur if altitude is ascended very rapidly or if you are staying at very high altitude for a week or more.
Symptoms to look out for include
Ignoring the signs and symptoms and continuing to ascend to higher levels. This can make mild symptoms into severe cases of altitude sickness.
Ascend slowly and gradually when you get to altitudes above 3000m. This will give your body time to adapt.
As a general guide, the altitude you sleep at should not increase by more than 300 to 500m at a time.
Give your body 3-4 days to adapt before you start to ascend to higher levels and try to avoid flying in direct to high levels.
You are less likely to suffer from altitude sickness if you are trekking and sleeping in lower valleys at night compared to climbing a big summit like Everest.
You can also use medication to prevent altitude sickness. See below
Acetazolamide is a versatile medication, which has several applications. It is a popular and widely used treatment for the prevention or reduction for the symptoms of altitude sickness. Acetazolamide actively reduces the feelings of dizziness, nausea, headaches and shortness of breath that are associated with rapid ascents.
Acetazolamide is usually taken one to two days before you begin ascending. You continue taking it every day, finishing two days after the highest altitude has been reached.
Acetazolamide corrects the chemical imbalance that occurs when altitudes are climbed too rapidly. It increases the volume of urine produced and alters the acidity of the blood, which lowers the fluid content found in and around the brain and lungs.
If the correct procedures are followed, the effects of altitude sickness will normally subside in approximately 1-2 days. Taking Acetazolamide 250mg tablets, in conjunction with following the correct procedures, has shown to cut recovery time in half.
A person’s breathing patterns can by significantly altered when sleeping at high altitudes. Usually, the altered pattern is characterized as rapid, short breaths that are followed by prolonged pauses. This is considered normal and is not classed as being dangerous. However, it can result in poor quality sleep. Taking Acetazolamide has shown to improve this breathing pattern, which allows for a much better nights sleep.
They should not be used as a substitute for sensible acclimatisation
Mild cases of altitude sickness can be treated with rest, acclimatization and medication. When the symptoms have subsided it is usually fine to continue to ascend.
Severe cases of altitude sickness need medical attention and you need to descend to lower levels as soon as possible
Authored by
Andy is a co-founder and the Superintendent Pharmacist and Director at The Independent Pharmacy.
Reviewed by
Dan is an experienced pharmacist having spent time working in both primary and secondary care. He currently supports our clinical team by providing robust clinical governance review of our internal processes and information.
Or browse all treatments or conditions
