Harris also knows ibuprofen, which has been widely viewed as the best medicine for high-altitude headaches, can worsen the nausea that typically accompanies the headaches.

He wanted to find out whether acetaminophen, which doesn't cause nausea, would be as effective for high-altitude headaches. So he set out to answer the question -- by testing the two pain relievers on hikers trekking some 14,000 feet up in the mountains of Nepal.

The conclusion: Acetaminophen and ibuprofen are equally effective, both providing headache relief within a few hours, Harris and fellow researchers report in the May issue of the Journal of Emergency Medicine.

"Up until now, there hasn't been any evidence to suggest that there was anything better than ibuprofen" for high-altitude headaches, Harris says. "It had become accepted as the standard of treatment. Ours is the first study proving that acetaminophen is as effective as ibuprofen against high-altitude headaches."

Of course, quick relief -- without nausea -- is no small concern when you're thousands of feet up in the mountains in an area so remote that it takes 12 days to hike to the nearest road and five to seven days to hike to the nearest airstrip.

"If you aren't both physically fit and feeling well, then you stay put," Harris says.

This gives your body time to get acclimated to the higher elevations. "But," he says, "taking a rest day without a headache is much more fun."

You don't have to be hiking in the shadows of Mount Everest (news - web sites) to experience high-altitude headache, the primary symptom of "acute mountain sickness" -- a syndrome that also can cause not only nausea, but also sleeplessness, loss of appetite and fatigue.

Each year, according to the study, some 7 million people who travel to U.S. elevations over about 6,500 feet will suffer acute mountain sickness severe enough to limit activity.

The condition is common, for example, among skiers who head to the mountains of Colorado. "Suddenly, rather than going out and skiing hard and enjoying time on the slopes," Harris says, "they're moping around with headache and nausea, and suddenly their very expensive trip is being wasted."

In the double-blind study, Harris and colleagues surveyed hikers arriving at a Nepal camp and enrolled 74 who had symptoms of high-altitude headache. (The researchers excluded those who had a history of chronic headaches, migraines or allergy to ibuprofen or acetaminophen.)

Of the 74 patients, 39 received ibuprofen and 35 got acetaminophen, and all the patients took surveys measuring headache symptoms and severity before taking the medications and 30, 60 and 120 minutes after taking them.

Both groups reported a similar decrease in headache pain during the two-hour study period as well as slightly decreased levels of nausea.

None of the patients suffered a rare and sometimes dangerous complication of acute mountain sickness that can cause edema -- a buildup of fluid -- in the lungs or brain. Harris stresses people in high altitudes shouldn't continue to ascend if they suffer symptoms such as worsening headaches, shortness of breath and confusion.

For Harris, the three months of research in 1999 provided a chance to pursue two passions: high-altitude hiking and medicine.