Historically the distinction revolved around whether or not physical withdrawal symptoms occur when an individual discontinues using a drug; what we in the field now call "physical dependence". However, years of research has demonstrated to us that focusing on this physical versus psychological distinction is a distraction from the real issues at hand.
Strictly from a clinical perspective, it actually does not matter very much what physical withdrawal symptoms occur. Physical dependence is not that important, because even the dramatic withdrawal symptoms of heroin and alcohol addiction can now be easily managed with appropriate medications. Even more important, many of the most dangerous and addicting drugs, including methamphetamine and crack cocaine, do not produce very severe physical dependence symptoms upon withdrawal. What really matters most is whether or not a drug causes what we now know to be addiction. More specifically, the compulsive craving and use, despite all of the negative consequences.
This is the crux of how the Institute of Medicine, the American Psychiatric Association, and the American Medical Association define addiction and how we all should use the term. It is really only this compulsive quality of addiction that matters in the long run to the addict and to his or her family. Thus, the majority of the biomedical community now considers addiction, in its essence, to be a brain disease - a condition caused by persistent changes in brain structure and function. The changes in brain function results in compulsive craving that overwhelms all other motivations and is the root cause of the massive health and social problems associated with drug addiction. A definition of drug addiction that is commonly referred to is "a brain disease expressed in the form of compulsive behavior". It is important to correct the common misimpression that drug use, abuse and addiction are points on a single continuum along which one slides back and forth over time, moving from user to addict, then back to occasional user, then back to addict. Extensive research studies support the view that, once addicted, the individual has moved into a different state of being. Very few people appear able to successfully return to occasional use after having been truly addicted.
Unfortunately, we do not yet have a clear biological or behavioral marker of that transition from voluntary drug use to addiction. However, evidence is rapidly developing that point to an array of cellular and molecular changes in specific brain circuits. Moreover, many of these brain changes are common to all chemical addictions and some also are typical of other compulsive behaviors such as compulsive overeating.
The complexity of this brain disease is not atypical, because virtually no brain diseases are simply biological in nature. All, including stroke, Alzheimer's disease, schizophrenia, and clinical depression, include some behavioral and social aspects. What may make drug addiction seem unique among brain diseases, is that it does begin with a clearly voluntary behavior - the initial decision to use drugs or drink alcohol. Moreover, not everyone who ever uses drugs goes on to become addicted. Individuals differ substantially in how easily and quickly they become addicted and in their preferences for particular substances. Consistent with the bio-behavioral nature of addiction, these individual differences result from a combination of environmental and biological, particularly genetic, factors. In fact, estimates are that between 50 and 70 percent of the variability to becoming addicted can be accounted for by genetic factors. Although genetic characteristics may predispose individuals to be more or less susceptible to becoming addicted, genes do not doom one to become an addict. Over time the addict loses substantial control over his or her initially voluntary behavior, and it becomes compulsive. For many people these behaviors are truly uncontrollable, just like the behavioral expression of any other brain disease. Schizophrenics cannot control their hallucinations and delusions. Parkinsonâs patients cannot control their trembling. Clinically depressed patients cannot voluntarily control their moods. Thus, once one is addicted, the characteristics of the illness - and the addiction treatment approaches - are not that different from most other brain diseases. No matter how one develops an illness, once one has it, one is in the diseased state and needs treatment. In the case of the addict or alcoholic treatment is best defined as admission to a drug rehab, addiction treatment facility or alcoholism treatment facility. Please note that not every person requires an inpatient drug rehab or addiction treatment facility, but research shows that most individuals do require structure of some kind to break the vicious compulsive cycle associated with drug addiction and alcoholism.