It wouldn’t be a wipe-out of the population. You make it sound as if a majority of the population does illegal drugs (not including cannabis). They gave up their humanity the second they started getting addicted and doing anything in their power to get their next fix. A lot of this country’s property damage/loss is drug-related.
Of course, it wouldn’t be placed in effect immediately. A month-long warning through radio and televised broadcast would sufficiently reach most of the population. After that, it would depend on a person’s own moral and will to survive. If they’re that far in as to continue, they’re probably not doing much to help the country.