AA (Alcoholics Anonymous for those who don't know) pointed out decades ago that there were such people called "dry drunks". These were the people who might have managed to stay off the demon booze: but who still had the underlying pathologies which had led to their addiction in the first place. The 12 steps program is as much an attempt to deal with those pathologies as it is to stay off alcohol. In one of the more significant advances of recent years in drug treatment we've also incorporated this insight into drug addiction treatment.
The point is that just as millions drink lightly and responsibly there are those who take drugs who do not become addicts, even under the widest definitions of addiction. But there are those who most definitely do and we'd like to know what is the difference between these two groups before we try to design a program of drug treatment. For it might be that the underlying problem is what leads to the addiction, not purely the intake of drugs (or alcohol or anything else).
This insight has led to the development of dual diagnosis drug treatment. We can see clearly and obviously the problem of the addiction: but what might be the underlying pathology which leads to it? Clearly and obviously, we're only going to be able to cure the addiction if we can also deal with that underlying cause. For some of course the cause of the addiction is clear: it can indeed be simple physical addiction to the substance being taken, it can be to the psychological (as opposed to the physiological) effects. Or it might be some more deep seated disturbance in either the body or the psyche.
One of the treatment centers working with this dual diagnosis paradigm is the Pat Moore Foundation: click through any of the links to find out more about these techniques.