But never is.
Not intentionally anyway, but has been by accident.
Which is not the reason we ban anthrax.
No, we ban it because it's deadly
To others - self-administration is not the reason. Conversely, the theoretical possibility of slipping drugs to others is not why we ban them.
Anthrax is exactly similar in that they both follow the same logistic growth pattern
Except when they don't. From 1980 to 1995, consumption of the legal drug alcohol dropped by 23%, and from 1973 to 2006 consumption of legal addictive cigarettes dropped by 59%.
Cigarette usage is being assaulted from every direction. It is being heavily regulated, Taxed and maligned with it's own money. The status of cigarette usage and the various and diverse effort to eradicate it ought to be a case study for how any sort of prohibition might be enacted with minimal backlash.
Had the Alcohol prohibitionists followed a similar route they may have eventually achieved their objective. They made the mistake of pushing too hard and too fast. The Backlash did them in.
But the effort to eradicate cigarettes will not likely work with stronger drugs. While the cravings of cigarette smokers are persistent, they are nothing as compared to the cravings of a crack head or heroin user.
As for the drop in Alcohol usage, (assuming your numbers are correct) I can only surmise that those users substituted other things.