"The simpler the molecule, the better the drug. So the best drug is oxygen. Only two atoms. The second-best, nitrous oxide - a mere three atoms. The third-best, ethanol - nine. Past that, you're talking lots of atoms." From Neal Stephenson's Zodiac.
There is a little further background to this. The more complicated the molecule, the more unpredictable it is. Therefore, drugs like Cannabis, heroin,etc, are out of the window because of the increased chances of those complex substances fucking up your body.
Play it safe. Keep to Sangamons Principle.
"I used to be Straightedge, but now I adhere to Sangamons Principle."
"Why'd you change?"
"I like promiscuous sex and drink."