Not that I necessarily doubt the veracity of this claim but you should probably point to a better looking graphic than that. Where did you even find it?

Agreed, it's a shitty chart, but it's from a study The Lancet performed;

http://www.thelancet.com/journals/lancet/article/PIIS0140-67...

Wiki actually sums it up pretty well;

http://en.wikipedia.org/wiki/Substance_dependence#Dependence...