Consider the Mexican drug cartels, who maintain their grip on power and resources specifically because of the high profits caused by the high risk of trafficking illegal drugs. These are extremely violent criminals with lots of political and economic power, and they have murdered over 60000 people since 2006.
It's hard to imagine that even large numbers of simple abusers of even the hardest, most risky drugs would be able to pull off such a holocaust in even the worst case.