I'll stick to my big three, caffiene, booze, & tobacco.
You remember what happeneded when they made booze illegal?
Caffeine, the world's most consumed (psychoactive)drug...http://ngm.nationalgeographic.com/ngm/0501/feature1/
We all know the claims and counter-claims on both sides: Cannot overdose on Marijuana, you can OD on alcohol. You're more than likely not going to want to drive 120 on front street over there if you're on pot. etc...etc...
My friend "Bill" smokes the pot everyday. Did a few years ago for a couple of years, and recently started again a few months ago. He recently stopped drinking as much, also.
(I wrote more, but deleted it for some reason...ugh...)
Bill would say it's mostly harmless. The smoking Natural (American Spirit) Tobacco Cigarettes is what kills him.
Also agree that this "America's War on Drugs" is a big waste of resources.
Coju, the effect the link there refers to was even more amplified because beer, what they were drinking before, probably made them a little tipsy and a little tired all the time. When Tea and Coffee came around, they were not just buzzed from caffeine, but also less drunk from the beer. I imagine the effect was transformational.