Which, IMHO, is an argument for legalisation and regulation of cannabis. Alcohol is regulated; relatively safe varieties are easily available, and those selling liquor with ingredients considered unsafe (from poisonous ethanol to excessive amounts of thujone) face prosecution. With cannabis-induced psychosis looming as a public health issue, perhaps a law restricting the ratio of THC to cannabidiol would ameliorate the crisis?
The other solution, and one infinitely more culturally appropriate for the Anglo-Saxon world, is the familiar zero-tolerance Reaganite war-on-drugs approach. Perhaps if we build more prisons, jail more users and dealers (and perhaps execute a few particularly bad apples for good measure to put the fear of God into potheads), and institute a regime of mass surveillance and appropriate abridgements to civil liberties to catch offenders, then maybe, just maybe, the damned horse can fly we'll eventually achieve a drug-free society.