An interesting article was just passed to me. A study was done on a caged rat which chose cocaine laced water over plain water. A scientist proposed that it wasn't addiction, but boredom and unhappiness. The rat was placed in a social environment with other rats, called Rat Park, and he turned away from his "need" for cocaine. http://elitedaily.com/news/world/scientists-may-discovered-real-cause-addiction/915030/
The article makes some good arguments such as decriminalizing drugs might be the route to go but I think it's a gross oversimplification of addiction, in coming off as attributing it all to setting. Rehab is usually an enviornment which seeks to refocus addicts habits and lives and relapse is often frequent still. Also, heroin usage may have dropped for returning Vietnam vets but that may be kind of deceiving in suggesting that their addictions were completely displaced. Perhaps some of them turned to alcohol, barbituates, cocaine etc.
I'd imagine that it would be alot easier to overcome an addiction among non-judgmental rodents than it would be among human society. Humans can be so judgmental.
the way I see it, pleasurable drugs cause a plesser able response and our brain is wired to repeat what causes us pleasure. it is when we know longer know how to seek pleasure from anything else that it becomes a problem.