This is from Wikipedia I wonder if there is still no way of testing for them if that's the case here we go again! I know there are rumours going around that its being used.
Doping[edit]

Inhaling a xenon/oxygen mixture activates production of the transcription factor HIF-1-alpha, which leads to increased production of erythropoietin. The latter hormone is known to increase red blood cell production and athletes' performance. Xenon inhalation has been used for this purpose in Russia since at least 2004.[155] On August 31 2014 the World Anti Doping Agency (WADA) added Xenon (and Argon) to the list of prohibited substances and methods, although at this time there is no reliable drug test.[156]