Altitude sickness: causes and prevention

Build the climb into the itinerary rather than squeezing it into the days you have left. A common schedule: spend a night around 2,500–3,000 m to start acclimatising, then keep sleeping-altitude gains to about 500 m a day above 3,000 m, with a rest day every 1,000 m (check). On rest days, walk high and return to sleep low — a day hike to a higher point then back down helps.

Arriving by vehicle or plane at altitude is the classic trap. Cusco (about 3,400 m), Lhasa (about 3,650 m), La Paz (about 3,600 m) and many Himalaya trailheads put you high while you sleep on the first night (check). Take the first 24–48 hours easy: no long hikes, no alcohol, plenty of water, and early nights. If you can, break the journey with a night at an intermediate height.

Guided treks on popular routes — Everest base camp, Kilimanjaro, the Inca Trail, Annapurna — have standard acclimatisation profiles. Ask the operator what the sleeping altitudes are day by day, how many rest days are included, and what happens if someone in the group cannot continue. Itineraries with an extra day generally have better summit rates and fewer evacuations than the shortest ones (check).

Acetazolamide (sold as Diamox) speeds up acclimatisation and is used both to prevent and to treat mild symptoms. In most countries it needs a prescription, and it is not right for everyone — ask a travel doctor or pharmacist about your own health, allergies and interactions, and about the dose and timing (check). It can cause tingling in fingers and feet, and it makes fizzy drinks taste flat. It is not a substitute for a slow ascent.

Painkillers such as paracetamol or ibuprofen help altitude headaches. Anti-nausea medicine can help vomiting. Dexamethasone is a steroid used for serious cases and by some climbers as a rescue drug; it is a prescription medicine and should be carried with clear instructions, not used to keep climbing. Other options exist, and advice differs by country, so treat any specific drug plan as something to confirm with a clinician (check).

Portable oxygen cylinders and pressure bags (Gamow bags) are carried on some commercial expeditions and at some high-altitude clinics. They can pull someone back from a dangerous state while a descent is organised, but they do not fix the problem. If you rely on them and stay high, symptoms return. Check what your trek operator carries and whether the price is included.

Coca tea, coca leaves and herbal remedies are widely used in the Andes. They are traditional and may help you feel better, but there is no strong evidence that they prevent altitude illness (check). They are not a reason to climb faster.

Altitude sickness itself costs nothing to prevent; the money goes on the itinerary and the kit. An extra acclimatisation day on a guided trek is often the single best-value purchase. On Kilimanjaro, adding a day to a standard route typically adds a few hundred US dollars in park fees, guide and food; on Everest base camp treks, an extra night in a village costs a night's lodge fee plus meals. Prices vary by operator and season — treat any figure as a 2026 estimate and confirm with the operator (check).

Medical kit is cheap by comparison. Acetazolamide is a low-cost prescription in most countries; paracetamol and rehydration sachets cost a few dollars (check). A travel clinic consultation before a high-altitude trip is usually the largest fixed cost, and it is where you get the prescription, the dose and the warnings in writing.

Insurance is the part people get wrong. Many standard travel policies exclude trekking above a set altitude, often 3,000 m or 4,000 m, and exclude helicopter evacuation or mountaineering (check). Read the altitude clause and the activity list before you buy, and check whether evacuation from a trekking route is covered. If you are going above the limit, buy a policy that names the activity and the height.

Children generally acclimatise at similar rates to adults, but they may not describe symptoms clearly, so watch behaviour: irritability, poor sleep, vomiting, refusing food. Infants and very young children should not be taken to high altitude for recreation (check). Pregnant travellers should discuss any high-altitude travel with a doctor; some guidance advises avoiding altitudes above about 2,500 m (check).

People with heart or lung disease, sickle cell disease, severe anaemia, or a history of HAPE or HACE need medical advice before going high; for some conditions the advice is not to go (check). Sleep apnoea and some medicines also change breathing at altitude, so review your regular drugs with a clinician.

Some destinations add their own rules and risks. Tibet permits and guided-tour requirements mean you cannot simply arrive and climb at your own pace; many travellers fly into Lhasa and feel unwell on day one. In the Andes, the altitude of La Paz and Cusco hits immediately after landing. In the Alps, cable cars can put you above 3,000 m within an hour, which is enough to trigger symptoms in someone who then walks hard (check). On Kilimanjaro, the standard routes climb fast and the summit night is the highest-risk period (check).

If you have had altitude illness before, plan a slower ascent, consider preventive medicine with a doctor's advice, and set a clear turn-around rule with your group before the trip.

Short answers to the questions travellers ask most about altitude sickness.