: Some reports suggest that regimens of inhaling xenon or argon mixed with oxygen can increase the body's production of the protein hypoxia inducible factor 1 (HIF1). An increase in HIF1 creates more erythropoietin (EPO), which increases the number of red blood cells in the body and, hence, its oxygen efficiency. As a result, some athletes have adopted use of the gases in an effort to improve their performances. Now, the World Anti-Doping Agency (WADA), which governs many sports, has added both xenon and argon to its list of prohibited substances. However, there are no effective tests for whether an athlete has been using the gases. Why the gases have been banned when similar regimens, such as hypoxic chambers and oxygen tents, are still allowed has been questioned by some sports medicine experts.