What Is "Dex" in Mountain Climbing?

Low angle view of a person climbing a mountain

Known among mountaineers as “dex,” dexamethasone is a steroid used to treat high-altitude cerebral edema. Every year about 2 percent of mountain climbers suffer from this life-threatening condition, according to Ken Kamler’s 2005 article, “Steroids on Everest” on the National Geographic website. However, a trend has emerged in which mountaineers use dex to sustain performance and alleviate the symptoms -- nausea, fatigue, dizziness, confusion, mood swings -- of acute mountain sickness. The use of dex to increase exercise capacity for high altitude climbs is controversial and poses health risks.

Emergency Treatment

High-altitude cerebral edema is a condition in which your brain, feeling the lack of oxygen, will draw more blood to itself. According to Kamler, the brain’s glutted capillaries start to leak, which leads to inflammation and swelling. Your cerebellum -- responsible for coordination -- and cerebral cortex controlling aggression become compressed inside your skull. You can become disoriented and clumsy, which can result in fatal incidents on the peaks. By taking dexamethasone, you can stop the capillaries from leaking and brain from swelling. Your mind regains clarity while your body can function in a coordinated way.

Boosting Exercise Capacity

In a 2009 study published by the “American Journal of Respiratory and Critical Care Medicine, Swiss researchers revealed that dexamethasone taken prophylactically can lower pulmonary hypertension, or elevated pressure within the blood vessels fueling the lungs. When you exercise at high altitudes, this condition restricts your capacity to function. In this study, 23 climbers, who had a history of high-altitude pulmonary edema in which excess fluid builds in the lungs, exercised on a stationary cycle at low elevation while being tested for oxygen uptake. The climbers were then given dexamethasone, tadalafil or a placebo. A second round of cardio exercise and tests were conducted at an altitude of almost 15,000 feet. Those climbers who took the dexamethasone experienced a smaller increase in heart rate, a higher VO2max, or maximal oxygen uptake, and much less acute mountain sickness than those in the other groups.

Mechanisms and Usage

Dexamethasone can increase your exercise capacity via various mechanisms. For example, it boosts the amount of nitric oxide in your system, reducing the pressure in your pulmonary arteries. It enhances your body’s ability to remove sodium and water, which facilitates the diffusion of oxygen. Because it eases inflammation, dex helps you to achieve a positive frame of mind. While a single dose can be life-saving in the case of high-altitude cerebral edema, some climbers are regularly taking dex prophylactically before the effects of high altitude have yet to kick in. They claim that the steroid use equates to the use of supplemental oxygen, both of which make a high-altitude climb easier, according to Kamler.


Researchers in the 2009 study warn that use of steroids by mountaineers can have side effects. Dex can impair your body’s inflammatory reaction to infection as well as boost the glucose levels in your blood. Prolonged use can result in osteoporosis, thickening of your skin and a decrease in muscle. Do not use dex unless you have a prescription from your doctor. In addition, the effects of taking steroids are similar to that of drug dependency. Over time, your body becomes less responsive to dex, so you’ll have to take more of the steroid to get the same result. If you’re in the middle of a climb and run out of the steroid, your body is that much less acclimated to high altitudes and the effects of acute mountain sickness will be much more pronounced.