Why not take all that speed and adulterate it with something that will not kill users immediately but cause debilitating symptoms the gradually lead to death. Symptoms resulting in sterility along the path would not be a bad thing. Intel agencies should take over the manufacturers’ labs and adulterate every future dose until the demand is gone. There you go, a simple and effective solution.
Slip in some LSD...
Diarrhea would be awesome. It's not hard to die from dehydration with gluteal volcanism.