Preventing altitude sickness 

Proper acclimatisation to altitudes of 2,500m (just over 8,200 feet) or above is the best way to prevent altitude sickness. Ascending slowly will give your body time to adapt to the change in altitude.

When booking a trip yourself, try to include two or three days to acclimatise. If you're booking a package holiday, check the itineraries of different providers to find a package that allows a few days for acclimatisation. If possible, you should try to avoid flying directly to a high altitude.

Some itineraries are more likely to cause problems with acclimatisation than others. For example, a trekking holiday that involves crossing ridges or low peaks but sleeping in the valleys is less likely to give rise to problems with altitude sickness than a climb up an isolated peak such as Kilimanjaro. 

It's unusual to get severe altitude sickness during most walking, climbing or skiing holidays to the Alps. Overnight accommodation is usually in valleys or mountain huts at heights of around 3,000m (9,842 feet) above sea level. 

However, acclimatisation for the higher mountains in the Alps will make a successful ascent more likely and safer. Before setting out for peaks over 3,500m (11,482 feet), it's sensible to have spent a few days climbing lower peaks to acclimatise.

It's not only on trekking or climbing holidays that high altitudes are reached – for example, some parts of the Colorado Rockies can be reached by road despite being over 3,500m.

Climb gradually

Once you're above 3,000m (10,000 feet), don't increase the altitude at which you sleep by more than 300-500m a night. You can go up higher during the day, but each night go back down to a camp that's no more than 300-500m higher than the previous night's camp.

Some holiday companies offer trips to climb a mountain in a short space of time, such as climbing Mont Blanc over a couple of days. If you're not already acclimatised, climbing at this rate is likely to lead to symptoms of altitude sickness. It would be better to attempt the climb at the end of a two-week holiday after you've acclimatised by climbing a few lower peaks first.


Medicines would normally only be considered for preventing altitude sickness if rapid ascent cannot be avoided.


Research has shown that acetazolamide (Diamox, which is licensed to treat glaucoma) can help prevent symptoms of altitude sickness. It's thought that acetazolamide works by correcting the chemical imbalance of the blood, caused by ascending quickly to high altitude.

In the UK, acetazolamide is not licensed for preventing (or treating) altitude sickness. However, it may sometimes be considered for 'off-label' use to prevent altitude sickness in people who may be at risk of developing it. Read more about unlicensed medicines.

To prevent altitude sickness, the recommended dose of acetazolamide is usually 125mg or 250mg twice a day. You should begin taking the medication one to two days before you start to ascend and continue to take it while ascending.

You may also be advised to take it for a day or two after you've reached your highest altitude. If you feel unwell while you're ascending, acetazolamide will not prevent you feeling worse and the only treatment is to descend or to rest.  

There are a number of common but minor side effects associated with acetazolamide, including numbness or tingling of the face, fingers or toes. Some people find these quite distressing, so doctors often suggest trying it at home for two days before travelling if you're likely to use it at altitude.

You should let your doctor know if you have any allergies to any medicines before acetazolamide is prescribed. Your doctor will also check your medical history to see if acetazolamide is suitable for you. 


Dexamethasone isn't usually recommended for preventing altitude sickness, but may be provided for the emergency treatment of high altitude cerebral oedema (HACE).

Further advice

As well as acclimatising properly and taking prescription medication, you should also follow the advice outlined below.

  • If you start to develop mild symptoms of altitude sickness, stay at your current altitude until your symptoms improve.
  • If your symptoms get worse, immediately descend from your current altitude.
  • Make sure everyone you're travelling with has fully acclimatised before going any higher.
  • When ascending above 3,000m, try to have a rest day every three days – this is where you may climb higher, but return to sleep at the same altitude as the night before.
  • Keep well hydrated by drinking plenty of fluids.
  • Eat a high-calorie diet while at altitude.
  • Don't smoke, drink alcohol or use medication such as tranquillisers and sleeping pills while you're at altitude, as they could make any symptoms of altitude sickness worse. Speak to your GP if you're unsure.
  • Remember, the risk of sunburn and sunstroke increases at altitude, so take full precautions to prevent them happening. In particular, make sure you have appropriate eye protection – specialist sunglasses, snow goggles or equivalent – and use them to prevent snowblindness, even if it's hazy. 

What to pack

  • sunglasses
  • sun protection cream
  • lip balm
  • water purification system with iodine tablets
  • means of communication – mobile phones now work in some high-altitude areas, including Kilimanjaro, but for other mountains you may need a satellite phone
  • plastic whistle – six blasts and a pause is the internationally recognised distress signal
  • first aid kit
  • head torch and batteries

Page last reviewed: 28/04/2015

Next review due: 28/04/2017