A drug is anything that alters your soul through matter.
If you eat enough paper, it will make you trip. If only you wouldn't die before you had the right ammount. Anything will make you trip. It's just, some things .. it takes less of it.
Food will alter your chemistry, your blood, the way your neurotransmitters work, and how you and your soul work it out.. well. Anyway.

Sugar is a drug. You can't peddle sugar unless you're a horse though- or 5 years old.

For conversation's sake though.. And to further delve in the illusion that human beings can communicate with one another on an abstract level- ..
I think anything society has a fit about is likely what we call a drug. For conversation's sake. Alcohol, caffeine, all of the fed restrictred substances- everything from tobacco to heroin and ibuprofen.

I don't think wether it's a legal or unrestricted substance really defines something to be a drug or not. Look at the history of cocaine, opium- Was cocaine not a drug until societies regulated it? :) MDMA (ecstasy, i believe) was entirely fine a few decades ago. Would we say it's not a drug? If it became deregulated, would we no longer call it a drug? :)

I don't think this topic is off the realm of coding. Maybe it's just me who's a dirty ba5+ard whose friends are all ex junkies and social deviants, hermits and computer n3rds and wh0r35. It seems to me that if you look at a chunk of the geek population, there are a lot of eccentrics and extremists- die hard religious gurus and or paper clip snorting addicts.