Portugal decriminalized drugs in mid-2001. 

The effect on drug use has been a dramatic decrease at the same time when drug usage rates in the rest of Europe have been increasing. Glen Greenwald has more.

Drugs should be legal because you own your body, and the idea of a consensual crime where you are both victim and perpetrator, is anti-freedom and irrational. But for pragmatists out there who can’t get on board because they think that legalizing drugs will result in more drug usage, here is the evidence that it will not.

http://txfx.net/2009/04/08/drug-use-in-portugal-plunges-after-decriminalization