According to an article in The Economist, Russia has been using xenon as a performance-enhancer for a few years now. A 2010 document produced by the State Research Institute of the Ministry of Defence advises on how to use the gas. Before competition it can help with listlessness and sleep disruption, and afterwards it can improve recovery.
The manual recommends a 50:50 mixture of xenon and oxygen, inhaled for a few minutes, ideally before going to bed. The gas’s action continues for 48 to 72 hours, so it should be repeated every few days.
Xenon doesn’t just stimulate EPO production. Because it works by activating production of a protein called Hif-1 alpha, which in turn causes production of other hormones as well as EPO, the manual claims its benefits include increasing heart and lung capacity, preventing muscle fatigue, boosting testosterone and improving an athlete’s mood.
And the gas appears to have been used in past Olympics. The website of Atom Medical Centre, a Russian medical-xenon producer, cites national honours the company received for its efforts in preparing athletes for the 2004 summer Olympics and the 2006 winter games.
BTW, inhaling Xenon has an interesting (short time) effect on your voice