What if we cut off all their supply and let them go cold turkey. All heroin is gone.
Infect the crop with a genetic strain that makes all future crops unable to produce seed—like the genetically modified corn we hear about.
If you can convince the people to hang on through three weeks of sheer hell and turmoil while they come down off their addiction and /or start a new one, I suppose it would work. Or get the addicts to volunteer to be housed in a prison where we can administer some meds for the step down to reality. I don’t think you’ll succeed with either plan.