With 20 states having now legalized medical marijuana use, and two (Washington and Colorado) having legalized recreational use of marijuana, the days of legal prohibition of use of marijuana for recreational as well as for medical purposes seem numbered. The case for prohibiting marijuana was never strong. It is a mind-altering drug, but no more so than alcohol, and it is considered less likely to induce violent behavior, and in general to have less destructive effects on the heavy user, the “addict.” There is little evidence that it is a “gateway” drug, in the sense that use of it induces...