If you’re planning to go to a mountain resort or other high-altitude destination, there’s a chance that altitude sickness could cloud your trip. Also called acute mountain sickness (AMS), it affects at least 25 percent of travelers to the Colorado Rockies, for example, and 50 percent of people who go to Cusco in Peru or trek in the Himalayas. It’s hard to predict if you will get sick, but the higher the altitude and the faster you ascend, the greater your risk. Some people are also just more susceptible.
AMS occurs most often at elevations higher than 8,000 feet above sea level. As you go higher, the air gets thinner and you inhale less oxygen per breath. Symptoms, which usually begin six to 12 hours after arrival, include headaches, shortness of breath, lightheadedness, fatigue and nausea. You may also feel irritable and have trouble sleeping until you adjust (acclimatize), which can take a few days.
You may think that being fit would protect you from altitude sickness. Not true. Even world-class athletes can develop AMS if they don’t take precautions. It’s not related to gender or age, either—though younger people may be more likely to exert themselves at high altitude, which can increase both the incidence and severity of AMS. Smokers are not at increased risk, but having a cigarette at high altitude can impair acclimatization and intensify symptoms. People with certain pre-existing conditions, including chronic lung or heart ailments, may have a more difficult time at high altitudes and should get medical advice beforehand; in some cases, they may be advised not to go.
Keeping altitude sickness at bay
The best way to avoid AMS is to ascend gradually. A common recommendation is to spend at least one day acclimatizing at an intermediate level (such as 7,000 feet) and ascend from there, at a rate of about 1,000 feet a day. That may be possible if you’re hiking or driving to your final destination— but not if you’re flying directly. In that case, here are other steps to take:
- Talk to your doctor about prescription acetazolamide (brand name Diamox and others), the drug of choice for preventing AMS. It works, in part, by making the blood more acidic, which increases ventilation and therefore improves oxygen saturation in the blood. The recommended prophylactic dose is 125 milligrams twice a day. According to a 2019 study in Wilderness & Environmental Medicine of 73 trekkers in Nepal, just half that dose (62.5 milligrams twice a day) may be as effective, though it didn't reduce side effects, which may include increased urination, altered taste, headaches, and a “pins-and-needles” skin sensation (parasthesia). Acetazolamide doesn’t work for everyone, and some people, including those with sulfa allergies, should avoid it.
- Alternatively, consider ibuprofen. In a 2012 study in the Annals of Emergency Medicine, people who took this over-the-counter pain reliever were less likely to develop AMS when they climbed from 4,100 feet to 12,570 feet in the White Mountains of California, compared to those taking a placebo. The dose was 600 milligrams, three times a day, starting six hours before ascending. Another study, in Wilderness & Environmental Medicine in 2010, found ibuprofen as effective as acetazolamide in trekkers in Nepal. Separate from its analgesic effects, ibuprofen inhibits prostaglandins and other inflammatory substances that can contribute to tissue swelling in the brain. Some earlier research has shown possible benefit from aspirin against high altitude headache as well, but mixed results for naproxen.
Or consider acetaminophen. A 2017 study in Wilderness & Environmental Medicine compared acetaminophen (1,000 milligrams) to ibuprofen (600 milligrams) in 225 partially acclimatized people trekking at elevation above 14,000 feet in Nepal. Each group took the assigned pain reliever three times a day until they reached 16,000 feet. Though 25 people in the acetaminophen group (22 percent) developed AMS compared to 18 (16 percent) in the ibuprofen group, the difference was not statistically significant—plus there was no significant difference in severity of symptoms in those who did get AMS, leading the investigators to conclude that “any differences [between the two drugs], should they exist, are likely small and of questionable clinical importance.” Unlike ibuprofen and other nonsteroidal anti-inflammatory drugs, acetaminophen works primarily through its analgesic action. That it helped in the study means that AMS may involve other pathways besides inflammation.
- If you go straight to a high altitude, try to spend your first day relaxing. Avoid strenuous exercise until you acclimatize. Drink fluids frequently. Don’t smoke.
- Don’t count on natural remedies touted for altitude sickness. Studies on the herb ginkgo biloba have had conflicting results. And a review of studies found no benefit from antioxidants (vitamins C, E and alpha-lipoic acid) or magnesium. Interestingly, a paper in the Journal of Travel Medicine noted that using coca leaf products, a traditional remedy often given to high-altitude travelers in South America, could increase AMS symptoms.
Worst-case scenario: For most people, AMS is short-lived and relatively minor. But in some cases, notably above 9,800 feet, it can progress to high-altitude cerebral or pulmonary edema. These are life-threatening conditions, characterized by such symptoms as mental confusion, difficulty maintaining balance, extreme shortness of breath and severe cough. If you experience any of these symptoms, you must immediately descend to lower altitude and get medical treatment.
Originally published November 11, 2013; updated March 12, 2019.
Also see Jet Lag: Causes and Treatment.