Altitude Sickness in Climbers and Efficacy of NSAIDs Trial (ASCENT): randomized, controlled trial of ibuprofen versus placebo for prevention of altitude illness

Wilderness Environ Med. 2012 Dec;23(4):307-15. doi: 10.1016/j.wem.2012.08.001. Epub 2012 Oct 24.


Objective: To study the effectiveness of ibuprofen versus placebo in preventing acute mountain sickness (AMS) and high altitude headache (HAH).

Methods: Double-blind, randomized, placebo-controlled trial.

Results: Two hundred ninety-four healthy Western trekkers were recruited on the Everest approach at 4280 m or 4358 m and randomly assigned to receive either 600 mg of ibuprofen or placebo 3 times daily before and during ascent to 4928 m. One hundred eighty-three of 294 participants completed the trial. Of the participants who did not complete the trial, 62 were lost to follow-up and another 49 broke trial protocol. In an intent-to-treat analysis (232 participants), ibuprofen was found to be more effective than placebo in reducing the incidence of AMS (24.4% vs 40.4%; P = .01) and the incidence of HAH (42.3% vs 60.5%; P < .01). Ibuprofen was also superior to placebo in reducing the severity of HAH (4.9% vs 14.7%; P = .01). The end point of oxygen saturation was also higher in the ibuprofen group (80.8 % vs 82.4%; P = .035). For the 183 participants who completed the trial and conformed to the protocol, the incidence of AMS between placebo and treatment groups was not significant (32.9% vs 22.7%; P = .129 for AMS incidence, 9.6% vs 8.2%; P = .74 for AMS severity, 54.8% vs 42.7%; P = .11 for HAH incidence, and 8.2% vs 3.6%; P = .18 for HAH severity).

Conclusions: Ibuprofen was found to be effective in preventing AMS in the intent-to-treat analysis group but not in those who completed the trial. This loss of significance in the subjects who completed the trial may be explained by persons in the placebo group having a higher burden of illness and associated decreased compliance with the protocol. An important limitation of this study may be the possibility that ibuprofen can mask headache, which is a compulsory criterion for the diagnosis of AMS.

Publication types

  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Altitude Sickness / epidemiology
  • Altitude Sickness / prevention & control*
  • Anti-Inflammatory Agents, Non-Steroidal / pharmacology*
  • Double-Blind Method
  • Female
  • Humans
  • Ibuprofen / pharmacology*
  • Incidence
  • Lost to Follow-Up
  • Male
  • Mountaineering
  • Patient Compliance
  • Severity of Illness Index
  • Surveys and Questionnaires


  • Anti-Inflammatory Agents, Non-Steroidal
  • Ibuprofen