Altitude sickness: symptoms, prevention and safe ascent

Plan the ascent so your sleeping altitude rises gradually, with rest days built in. The commonly quoted rule of thumb is a modest daily gain above 2,500 m plus a rest day every so often — follow the guidance of the operator, park authority or doctor you are travelling with.

Drink enough water, eat normally, and go easy on alcohol and heavy meals during the first days at height. The practical version is to keep urine pale and to drink more than you would at sea level.

Medication can help. Acetazolamide is widely used to prevent and treat altitude sickness, but the dose, when to start it, who should not take it and whether you need a prescription are a decision for a doctor, not a web page. Some travellers also carry other drugs prescribed in advance.

Watch yourself rather than a number. A pulse oximeter reading can be a useful extra signal, but it varies between people and devices. Symptoms and how they are trending matter more than a single reading.

The main cost of doing this properly is time. Extra nights at lower altitude add days to an itinerary, and on a guided trek those nights are usually charged as accommodation, food and sometimes a permit or guide day. Rates vary by country and operator — check with the operator.

Medication costs depend on the drug, the country and whether it is covered by your insurance. Travel insurance that covers trekking and high-altitude evacuation is a separate cost and is worth checking before you book, because many standard policies exclude altitude above a stated limit.

If you do get ill, the cost of a changed itinerary, a helicopter evacuation or a hospital visit can be large. Check what your policy actually covers for the altitude you plan to reach.

Flying or driving straight to a high city is the classic trigger: there is no acclimatisation on the way up, so symptoms can appear within hours. A night or two lower down before going higher is a common way to soften that.

People with heart or lung conditions, pregnant travellers, and anyone taking regular medication should get individual advice before going high. Whether a given condition rules out a given altitude depends on the person and the destination — ask a doctor.

Children can be affected and may not describe symptoms clearly, so watch for irritability, poor sleep, vomiting or unusual tiredness. Any decision about taking a child high should come from a doctor.

The table below sets out how the two broad approaches differ in practice. Treat it as a way to compare strategies, not as a set of numbers to plan against.

The pattern is consistent across sources: the faster the gain in sleeping altitude, the more likely symptoms are, and the more important it is to have a plan for stopping and descending.

Short answers to the questions travellers ask most about altitude sickness. Each answer is general information, not medical advice.

This page is written from the official government travel-health guidance listed below. Where a figure could not be confirmed from those sources it is marked check rather than filled in from memory.