Portugal's drug decriminalization experiment largely looks like a success:
[T]here’s evidence that Portugal’s great drug experiment not only didn’t blow up in its face; it may have actually worked. More addicts are in treatment. Drug use among youths has declined in recent years. Life in Casal Ventoso, Lisbon’s troubled neighborhood, has improved. And new research, published in the British Journal of Criminology, documents just how much things have changed in Portugal. Coauthors Caitlin Elizabeth Hughes and Alex Stevens report a 63 percent increase in the number of Portuguese drug users in treatment and, shortly after the reforms took hold, a 499 percent increase in the amount of drugs seized indications, the authors argue, that police officers, freed up from focusing on small-time possession, have been able to target big-time traffickers while drug addicts, no longer in danger of going to prison, have been able to get the help they need.
Drum has further questions:
One of the big questions in drug policy is just how elastic the demand for illegal drugs is. It makes sense that if you lower the price of marijuana or cocaine, use will go up, and that lowered price can be in the form of either actual dollars or reduced risk of being fined or arrested. But as always, the question is: how much? If decriminalization increases drug use by a few percent, that's not bad especially considering the massive downsides of the war on drugs. But if it doubles or triples drug use, the consequences are more severe. The more data we have on this, the better.