Opium was prohibited even after the opium wars. That's not a good example of non-prohibition but instead the knockon effects of worst of both worlds informal, capricious quasi-legality.
> The counter-example is Prohibition (which was an abject failure), but maybe this is (at least in part) due to the cultural importance of alcohol of so many people. I don't really think cocaine or meth are such cultural lynchpins.
I mean, people haven't really stopped doing Cocaine or Meth, and the most negative effects of prohibition (extremely violent organized crime) still seem to be present.