This is a research study on Altitude Illness. From the information collected and studied in this project we hope to learn more about Altitude Illness, including factors that may affect and prevent the development and progression of this condition. We hope to learn if the commonly used non-steroidal anti-inflammatory medication, ibuprofen can prevent altitude illness. Possible participants in this study are healthy adults who indicated they would like to participate, learn about altitude illness, and desire to hike Barcroft Peak. Stanford University researchers hope to enroll about 100 participants.