Descent is the single most reliable treatment for altitude sickness, and a slow, staged ascent is the single most reliable way to prevent it. Between those two bookends sits a range of medications, practical strategies, and emergency tools that can make the difference between a miserable trip and a dangerous one. The condition is common enough that most people who travel above about 2,500 meters (roughly 8,000 feet) have a real chance of experiencing it, yet preventable enough that a little planning goes a long way.
What Happens in Your Body at Altitude
As you climb, the air pressure drops and each breath delivers less oxygen to your lungs. Your body’s first reflex is to breathe faster and deeper. That hyperventilation blows off carbon dioxide and shifts your blood chemistry toward a more alkaline state, triggering a cascade of adjustments in which your kidneys work to restore balance by excreting bicarbonate.1PubMed Central. Do over 200 million healthy altitude residents really suffer from chronic Acid-base disorders? These adjustments take time. When the ascent is faster than the body can compensate, the result is acute mountain sickness, or AMS.
The hallmark symptom is headache, often accompanied by nausea, fatigue, dizziness, and poor sleep. Researchers have linked more severe cases to changes in how permeable the blood-brain barrier becomes under low-oxygen conditions. Brain imaging in the most serious cases shows swelling consistent with fluid leaking into brain tissue, and ordinary AMS often precedes those more dangerous states.2Travel Medicine and Infectious Disease. What role does the blood brain barrier play in acute mountain sickness? Other mechanisms, including shifts in kidney hormone signaling and fluid balance, also play a role.3Quality in Sport. Acute mountain sickness: pathophysiology and prevention
Recognizing Altitude Sickness
Diagnosis in the field relies on symptom scoring rather than lab tests. The Lake Louise Acute Mountain Sickness Score, in use since 1991 and updated in 2018, asks you to rate headache, gastrointestinal symptoms, fatigue, and dizziness on a scale. A score of three or more, with headache present, after a recent gain in altitude counts as AMS.4PubMed Central. The 2018 Lake Louise Acute Mountain Sickness Score You don’t need a doctor to use it. The scoring system was designed for trekkers and researchers in remote settings, and its simplicity is the point: if you have a headache and feel lousy after ascending, take it seriously.
Mild AMS is unpleasant but self-limiting if managed correctly. The danger comes when people push through worsening symptoms, because AMS can progress to two life-threatening conditions: high-altitude cerebral edema (HACE), which involves dangerous brain swelling, and high-altitude pulmonary edema (HAPE), in which fluid fills the lungs. Both require aggressive treatment and, ideally, immediate descent.5PubMed Central. High-altitude medicine
Prevention Through Gradual Ascent
The most effective prevention strategy costs nothing and requires no medication: climb slowly. The standard recommendation is to limit your sleeping altitude gain to about 300–500 meters per day once above 2,500 meters, with a rest day every 1,000 meters or so. This gives your kidneys time to adjust blood chemistry, your bone marrow time to ramp up red blood cell production, and your breathing centers time to recalibrate.
For people who can’t control their ascent rate, such as those flying directly into high-altitude cities or deploying for military or humanitarian operations, pre-acclimatization offers a partial substitute. Spending time at simulated altitude (in a hypobaric chamber or using a hypoxic tent) before the trip can lower AMS risk measurably. One analysis found that the reduction in AMS risk ranged from about 12% to 73% depending on how long the pre-acclimatization exposure lasted, with duration explaining about three-quarters of the variation in protection.6PubMed Central. Time requirements of pre-acclimatization at simulated altitude to prevent acute mountain sickness In practical terms, more hours in a hypoxic environment before the trip meant more protection during it. A weekend of sleeping in a hypoxic tent helps, but not as much as several weeks of intermittent exposure.
Acetazolamide for Prevention
Acetazolamide is the best-studied drug for preventing altitude sickness. It works by nudging your kidneys to excrete more bicarbonate, which acidifies the blood slightly and tricks the brain into breathing faster and deeper. The net effect is higher blood oxygen levels and a smoother transition to altitude. In one trial comparing acetazolamide, ginkgo biloba, a combination of both, and placebo among Himalayan trekkers, AMS developed in about 34% of the placebo group versus 12% of those taking acetazolamide at 250 mg twice daily. That translated to needing to treat only four people to prevent one case.7PubMed Central. Randomised, double blind, placebo controlled comparison of ginkgo biloba and acetazolamide for prevention of acute mountain sickness among Himalayan trekkers: the prevention of high altitude illness trial (PHAIT)
Timing matters. Research comparing early versus late dosing found that people who started acetazolamide before ascending maintained more stable blood pH and had meaningfully better oxygen levels at altitude than those on placebo. The acetazolamide group’s blood pH barely budged from sea-level values even on the first day at altitude, while the placebo group’s pH jumped sharply.8PubMed Central. Acetazolamide pre-treatment before ascending to high altitudes: when to start? Most guidelines suggest starting the drug one to two days before ascent. Common side effects include tingling in the fingers and toes, increased urination, and a flat taste to carbonated drinks. Those side effects are annoying but harmless, and they’re actually a sign the drug is working.
Dexamethasone, Ibuprofen, and Other Medications
Dexamethasone, a steroid, is the main alternative for people who can’t tolerate acetazolamide or who are allergic to sulfa drugs. It reduces inflammation and appears to stabilize the blood-brain barrier, making it effective at preventing both AMS and the more severe HACE. Evidence suggests it works best above 4,000 meters, at doses of 8–16 mg per day.9PubMed Central. Dexamethasone for prevention of AMS, HACE, and HAPE and for limiting impairment of performance after rapid ascent to high altitude: a narrative review Unlike acetazolamide, dexamethasone doesn’t help your body acclimatize; it masks the problem by fighting the inflammatory response. That distinction matters: if you stop taking dexamethasone at altitude without having acclimatized, symptoms can come roaring back. For this reason, many clinicians prefer to use it as a treatment drug or as a short-term bridge rather than a long-term preventive.
For the headache component specifically, plain ibuprofen offers some protection. A meta-analysis of three randomized trials involving over 400 people found that high-altitude headache occurred in about 42% of those taking ibuprofen versus 57% on placebo. Severe headache was considerably rarer in the ibuprofen group, dropping from about 10% to 3%.10PubMed Central. Efficacy of ibuprofen on prevention of high altitude headache: A systematic review and meta-analysis Ibuprofen won’t prevent the nausea, dizziness, or other non-headache symptoms of AMS, so it’s not a substitute for acetazolamide. But for someone who primarily dreads the headache and is heading to moderate altitude, it’s an accessible over-the-counter option to carry along.
What to Do When Symptoms Hit
If you develop AMS, the first rule is simple: stop ascending. Many mild cases resolve on their own within a day or two if you stay at the same altitude and rest. Acetazolamide can be started as a treatment even if you didn’t take it preventively, and ibuprofen or acetaminophen can manage the headache. Staying well hydrated matters, though drinking water isn’t a cure. The evidence supports prioritizing carbohydrate-rich foods during high-altitude activity, partly because carbohydrates produce more carbon dioxide per unit of oxygen consumed, which may gently support ventilation.11PubMed Central. Nutrition and Hydration for High-Altitude Alpinism: A Narrative Review
If symptoms are moderate or worsening, descend. Even a few hundred meters of descent often brings dramatic relief. When descent isn’t immediately possible, supplemental oxygen rapidly reverses the symptoms and signs of both AMS and HAPE by increasing the oxygen pressure in each breath and correcting the underlying oxygen deficit.12PubMed Central. ABC of oxygen: oxygen at high altitude Flow rates of two to four liters per minute are usually sufficient for AMS. HAPE may need higher flow rates, and HACE demands both oxygen and urgent descent if at all possible.
Emergency Tools When You Can’t Descend
In remote settings where descent is delayed by weather, terrain, or logistics, two tools can buy critical time. The Gamow bag is an inflatable fabric chamber that encloses the patient. A foot pump pressurizes the bag, simulating a drop in altitude of roughly 1,500–2,000 meters. It has been shown to relieve AMS symptoms and can be life-saving when a helicopter can’t fly.13PubMed. A self-contained life support system designed for use with a portable hyperbaric chamber The limitation is that the benefit fades once the patient leaves the bag, so it works best as a bridge to evacuation rather than a definitive treatment.
For HAPE specifically, the calcium channel blocker nifedipine can be a backup when oxygen and descent are unavailable. HAPE is driven by abnormally high pressure in the lung’s blood vessels, and nifedipine lowers that pressure. In a small clinical study, treatment of patients with confirmed HAPE using nifedipine lowered pulmonary artery pressure, improved oxygenation, and cleared the fluid visible on chest X-rays.14PubMed. Prevention and treatment of high altitude pulmonary edema by a calcium channel blocker Nifedipine is most relevant for people with a known history of HAPE who are returning to altitude, and it’s typically carried as an emergency drug on expeditions above 4,000 meters.
Fitness Does Not Protect You
One of the most persistent myths about altitude sickness is that fit people are immune. Research specifically examining the relationship between physical fitness, exercise intensity during ascent, and AMS found that neither factor was an important predictor of who got sick.15Journal of Wilderness Medicine. Relationship of mountain sickness to physical fitness and exercise intensity during ascent Marathon runners and couch potatoes are roughly equally susceptible. If anything, very fit people may be at greater risk because they’re more likely to push a fast pace upward, and vigorous exertion at altitude can worsen symptoms.
The factors that do matter are ones you mostly can’t control: individual physiology, genetics, and your personal history. If you’ve had altitude sickness before, you’re more likely to get it again under similar conditions. Living at low altitude your whole life offers no opportunity to pre-adapt. Age is a mixed bag; younger adults may report AMS more often, but that could reflect more aggressive ascent profiles. People with pre-existing cardiovascular or respiratory conditions face additional complexity at altitude, and the interaction between altitude and chronic disease is still an area where the evidence is thin.16PubMed Central. Impact of High Altitude on Cardiovascular Health: Current Perspectives If you have a heart or lung condition, getting medical advice before a high-altitude trip is worth the effort.
Remedies That Don’t Work
Ginkgo biloba has been sold for years as a “natural” altitude sickness preventive, and early small studies gave it some credibility. But the largest and most rigorous trial, conducted among trekkers in the Himalayas, found that ginkgo was essentially no different from placebo. AMS rates were 35% in the ginkgo group and 34% in the placebo group, while acetazolamide cut the rate to 12%.7PubMed Central. Randomised, double blind, placebo controlled comparison of ginkgo biloba and acetazolamide for prevention of acute mountain sickness among Himalayan trekkers: the prevention of high altitude illness trial (PHAIT) The numbers are stark enough that ginkgo should be considered an ineffective remedy. Coca tea, popular in the Andes, has cultural significance and may ease nausea subjectively, but no robust trials demonstrate that it prevents AMS. Garlic, rhodiola, and various other herbal supplements circulate in trekking forums without strong evidence behind them.
Alcohol deserves mention, too. It’s a respiratory depressant, meaning it slows your breathing at the exact time your body needs to breathe more. Drinking at altitude can worsen symptoms, impair sleep quality (already poor at altitude), and accelerate dehydration. The temptation to celebrate reaching a summit or high camp with a drink is understandable, but it’s worth waiting until you’ve descended or fully acclimatized.
A Practical Checklist for High-Altitude Travel
Pulling together the evidence, a reasonable approach for someone heading above 2,500 meters looks like this:
- Plan a gradual ascent: Limit sleeping altitude gains to 300–500 meters per day above 2,500 meters. Build in rest days. If you’re flying directly to a high-altitude destination, plan light activity for the first day or two.
- Consider acetazolamide: Talk to a doctor about starting 125–250 mg twice daily, beginning one to two days before ascent. This is especially worthwhile if you have a history of AMS, are ascending faster than ideal, or are heading above 3,500 meters.
- Carry ibuprofen: Useful for headache prevention and treatment. Not a replacement for acetazolamide but a practical addition.
- Stay hydrated and eat well: Favor carbohydrate-rich meals. Don’t force excessive water, but match your increased fluid losses from dry air and exertion.
- Know your red flags: Confusion, loss of coordination, severe breathlessness at rest, or coughing up pink or frothy sputum are signs of HACE or HAPE. These demand immediate descent and emergency care.
- Don’t count on fitness: Train for the physical demands of the trip, but don’t assume that being in shape makes you altitude-proof.
How Permanent High-Altitude Populations Adapted
For a different perspective on altitude sickness, consider the roughly 140 million people worldwide who live above 2,500 meters year-round. Populations on the Tibetan Plateau, the Andean Altiplano, and the Ethiopian Highlands have lived at elevation for thousands of years, and their biology has changed in response. Tibetans in particular carry distinctive variants in a gene called EPAS1, which is involved in the body’s oxygen-sensing pathway. These variants dial down the gene’s activity, resulting in lower hemoglobin concentrations than you’d expect at altitude and a reduced pulmonary vasoconstriction response, both traits that protect against the chronic mountain sickness and HAPE that would otherwise plague long-term altitude residents.17Molecular Biology and Evolution. Down-Regulation of EPAS1 Transcription and Genetic Adaptation of Tibetans to High-Altitude Hypoxia
Research comparing Tibetans to Han Chinese living at the same altitude found differences across dozens of biological markers, including red blood cell characteristics, immune cell counts, and levels of the master hypoxia-sensing proteins HIF-1α and HIF-2α, all lower in the Tibetan group.18PubMed Central. Genetic and immune changes in Tibetan high-altitude populations contribute to biological adaptation to hypoxia Andean highlanders took a different evolutionary route, relying more on increased hemoglobin and higher oxygen-carrying capacity. Ethiopian highlanders appear to have yet another strategy that researchers are still working out. The takeaway for travelers is that the discomfort you feel at altitude is your body scrambling to do in days what these populations’ ancestors had millennia to solve. The machinery is similar, but the timeline is very different, which is precisely why gradual ascent, medication, and knowing when to turn around remain the foundation of staying safe at elevation.