The anti-doping rules are governed by the World Anti-Doping Code. It's a uniform and global set of requirements. Currently, cannabis is a prohibited substance in competition. It has a specific threshold associated with the tests we conduct. An athlete in competition found to have cannabis present in their system above that threshold would be subject to an anti-doping rule violation regardless of the legal and civil environment of whatever country they come from.
On November 28th, 2013. See this statement in context.