On Monday, American judo competitor Nick Delpopolo was expelled from the Olympics for doping with cannabis. (He says he accidentally ate a pot brownie.) The key word here is "doping"--if the situation were different, Delpopolo might just have been "using." Cannabis is on the Prohibited List, a catalogue of banned drugs maintained by the World Anti-Doping Agency, or WADA. Test positive for a drug on WADA's list? You're doping, and face dismissal from the Games. Test positive for anything else, even if it's illegal? No worries--you're free to compete. This is one powerful list. But why is cannabis, the users of which are not necessarily renowned for their athletic ability, on it?