Twenty-six: that’s the percentage drop in the likelihood of developing symptoms of acute mountain sickness (AMS)—headaches, dizziness, fatigue, and nausea—by popping an ibuprofen, according to a new study in the Annals of Emergency Medicine. In the study, participants hiked to the top of a 12,570-foot peak in California’s Sierra Nevada and spent the night. Of the 44 climbers who received three 600-milligram doses of ibuprofen during the hike, only 19 suffered from altitude sickness, whereas 29 of the 42 participants who took a placebo developed AMS. The author of the study, Grant Lipman, a professor at the Stanford University School of Medicine, speculates that less oxygen in the brain may cause it to swell with fluid and the ibuprofen simply helps reduce that swelling. “Ibuprofen could be an easy way to prevent AMS in a significant number of the tens of millions of people who travel to high altitudes each year,” says Lipman.