Those drugs still have to be shipped via a real postal system. Speculative scifi suggests that I will have a machine in my house that will produce drugs on the fly, with chemical reactions that are controlled by software.
Similarly, in Daniel Suarez's Daemon [2] he describes how a series of net connected people pass around individual parts that they have no idea the purpose of until they all get delivered to one guy who assembles them into a gun.
1 - http://www.amazon.com/Metatropolis-John-Scalzi/dp/B0058M5ZJ6 - "The Red in the Sky is Our Blood"
1) The printer is capable of "printing" complex compounds using individual atoms
2) The printer is pre-loaded with cocaine, LSD, MDMA...
My point being not everything can be printed...