The most useful way to lower your risk of altitude sickness is to give your body time to adjust: plan a gradual ascent, build in nights at the same elevation and do not keep climbing if symptoms begin. Acetazolamide may help when a high-risk itinerary cannot be changed, but it does not make a rapid ascent risk-free.
A slower ascent helps prevent altitude sickness
At altitude, lower air pressure means less oxygen is available with each breath. Your body needs time to adapt, especially during the first three to five days after you ascend. Risk depends on how high you sleep and how quickly your sleeping elevation increases—not simply how hard you exercise during the day.
The CDC Yellow Book and the Wilderness Medical Society’s 2024 clinical practice guidelines recommend gradual ascent. A useful plan is to spend two or three nights around 2,450–2,750 metres (8,000–9,000 feet) before going higher. Avoid going from a low elevation to sleeping at 2,750 metres (9,000 feet) or above in one day. Once above 3,000 metres (about 9,800 feet), aim to increase sleeping elevation by no more than 500 metres (1,650 feet) per night, with an extra acclimatization night for every 1,000 metres (3,300 feet) gained.
These are planning guides, not guarantees: some people need a slower schedule. If your route or flight takes you high quickly, consider whether you can sleep lower for a night or add days before continuing. Even a well-planned itinerary cannot prevent every case.
Fitness does not protect you from altitude illness
Being fit may help you handle physical activity, but training and physical fitness do not reduce your susceptibility to altitude illness. Children can be affected too, and a previous trip without symptoms is not a sure prediction for the next one—particularly if the sleeping altitude or ascent rate differs.
Acute mountain sickness (AMS), the most common form, often causes a headache with nausea, dizziness, fatigue or loss of appetite. Symptoms commonly start within hours of arriving or climbing higher, often during or after the first night. Pay attention to how you feel rather than assuming tiredness is just a sign of poor fitness.
When acetazolamide may be considered
Acetazolamide, also known by the brand name Diamox, helps the body acclimatize more quickly. A travel-health clinician may discuss it for someone at higher risk, such as a traveler who must fly rapidly to a high elevation or follow a route where a slower ascent is not practical. Current CDC travel guidance recommends a low threshold for preventive medication in some rapid-ascent situations. The medicine is an addition to sensible planning, not a substitute for it.
It can cause tingling in the fingers or toes, more frequent urination and changes in how some drinks taste. Before travel, discuss whether it is suitable for you, especially if you have kidney problems, are pregnant, take other medicines or have had a serious drug allergy. Sulfonamide-antibiotic allergy does not automatically mean acetazolamide is unsuitable, but a history of a severe reaction needs careful medical advice. Prescribing and availability rules differ by country, so arrange this conversation with a clinician before you leave rather than borrowing tablets or starting them without advice.
Symptoms that mean stop climbing or descend
If you develop possible AMS symptoms after ascending, do not go higher. Rest at the same elevation and monitor whether you improve. If symptoms worsen or do not improve, descend. Do not let a fixed itinerary or a group’s pace overrule how someone is doing.
Confusion, unusual drowsiness or difficulty walking straight can signal high-altitude cerebral edema (HACE). Breathlessness at rest, worsening cough or chest congestion can signal high-altitude pulmonary edema (HAPE). These are emergencies: arrange immediate descent and urgent medical help. If descent is delayed, seek emergency assistance and use oxygen if available; do not leave the affected person alone.
Before you travel, review your sleeping elevations and escape options with a travel-health clinician, particularly if your itinerary includes a rapid arrival above 3,400 metres (11,150 feet), a previous episode of serious altitude illness or limited access to help. If you are worried about symptoms at altitude, seek medical care promptly.
