How to Prevent Altitude Sickness: A Practical Guide

You booked the mountain trip, the ski week, or the high-altitude hike, and now you're worried a pounding headache and nausea could wreck the whole thing. It's a fair worry, but altitude sickness is largely preventable, and most cases are mild if you plan ahead.

The single most effective way to prevent altitude sickness is to ascend slowly so your body has time to adjust to thinner air. Below, we'll walk through exactly how to do that, when medication makes sense, and the warning signs that mean it's time to head down.

What is altitude sickness, and who gets it?

Altitude sickness happens when you climb to a high elevation faster than your body can adapt to the lower oxygen and air pressure. The mildest and most common form is acute mountain sickness (AMS). Its symptoms, including headache, fatigue, dizziness, nausea or loss of appetite, and disturbed sleep, typically appear 6 to 12 hours after arriving above about 2,500 m (8,200 ft).

Anyone can get it, regardless of age or fitness. Being young and athletic does not make you immune. The biggest predictors are how high you go, how fast you get there, and whether you've had altitude illness before. In rarer cases AMS can progress to dangerous conditions affecting the brain (HACE) or lungs (HAPE), which we cover below.

How to prevent altitude sickness: ascend gradually

Gradual, staged ascent is the single best way to prevent altitude sickness. The idea is simple: give your body extra days at moderate elevation so it can acclimatize before you go higher. The Cleveland Clinic recommends spending a night or two at an intermediate altitude to let your body adapt to lower oxygen and pressure.

The CDC offers specific targets for how fast to climb:

• Avoid going from below 1,200 m (4,000 ft) directly to a sleeping altitude above 2,750 m (9,000 ft) in a single day.
• Once you're above 3,000 m (9,850 ft), raise your sleeping altitude by no more than 500 m (1,600 ft) per day.
• Add an extra acclimatization day for every additional 1,000 m (3,300 ft) of gain.
• Remember it's your sleeping altitude that matters most; you can hike higher during the day, as long as you sleep lower ("climb high, sleep low").

Does medication prevent altitude sickness?

Sometimes a slow ascent isn't possible, such as flying straight into a high-altitude city. When rapid ascent is unavoidable, altitude illness rates approach 30 to 40 percent, which is why the CDC advises a low threshold for medication-based prevention.

Acetazolamide is the FDA-approved gold-standard preventive drug and is roughly 60 to 80 percent effective at reducing AMS. It works by causing a mild metabolic acidosis that stimulates breathing, increasing minute ventilation by about 10 to 20 percent at altitude and essentially mimicking natural acclimatization. Prophylaxis should begin 1 to 2 days before ascent and continue for about 2 days at your target altitude; the Wilderness Medical Society guidelines recommend starting a low dose the day or evening before you ascend. Acetazolamide is a prescription medication, so talk to a clinician before your trip about whether it's right for you.

If you can't take acetazolamide because of a sulfa-related allergy, the CDC notes that over-the-counter ibuprofen, taken at 600 mg every 8 hours, also helps prevent AMS. It's not quite as effective as acetazolamide, but it's inexpensive and well tolerated.

Who should consider preventive medication?

Not everyone needs medication. Many travelers prevent altitude sickness with careful ascent alone. But preventive medication is specifically recommended for higher-risk situations.

According to StatPearls and the Wilderness Medical Society, you're a good candidate for prophylaxis if any of the following apply:

• You have a prior history of altitude illness.
• Your first sleeping altitude will be above about 2,800 m.
• Your itinerary forces an ascent rate exceeding 500 m per day in sleeping-altitude gain.
• You're flying or driving directly to a high elevation with no time to acclimatize.

Everyday habits that help you acclimatize

Beyond ascent rate and medication, a few simple habits support your body as it adjusts. None of these replace a gradual climb, but they can make you more comfortable.

The Cleveland Clinic notes that carbohydrate-rich meals require less oxygen to digest than fatty foods and may help at altitude. Staying well hydrated, avoiding alcohol and sleeping medications in the first day or two, and easing off heavy exertion while you adjust are all sensible. And don't ignore early symptoms: a mild headache is a signal to stop climbing higher until you feel better, not to push through.

When to see a doctor or descend immediately

Mild AMS often improves with rest and not going any higher. But altitude sickness can become a medical emergency, and descent is the definitive treatment. Come down without delay if symptoms are severe or rapidly worsening.

Seek emergency help and descend right away for warning signs of the two dangerous forms of altitude illness:

• Brain (HACE): confusion, trouble walking straight, severe drowsiness, or a severe headache that doesn't respond to rest.
• Lungs (HAPE): breathlessness at rest, a wet or crackly cough, chest tightness, or unusual fatigue.
• Any symptoms that keep getting worse instead of better.