Self medication

Commonly addiction is called 'self medication'.  This is true in that all addiction probably begins with an anxiety disorder.  Alcohol, marijuania, and heroin, for instance are all anti anxiety medications.  They're the principal 'street valiums'.  The trouble with 'self administration' is that eventually there is a high risk with addictive medications for one to 'cross the line'.  The line is where 'quitting' is easy.  Cigarettes initially soothing have a very quick addictive potential.  No one quite knows for the individual how quickly a person can develop addiction to an addicting substance. Addicting substances are by street parlance any drug that 'has a street value'.  Drugs may cause physiological dependence such as insulin but it doesn't sell at a mark up on the street.
The trouble with the term 'self medication' is that it assumes an 'underlying disorder' without acknowledging that normal people can develop mental illness as a consequence of doing street drugs.
I once had an amusing argument with an old psychiatrist about this. He said "everyone who does cocaine has schizophrenia." I answer, "cocaine was used as a research drug because it 'mimicked' the symptons of schizophrenia. He retorted, rather aggressively, "anyone who did cocaine would have to be schizophrenic."
This is a typical problem of 'circular logic', a fallacy not uncommon in psychology and psychiaty and of course politics.
The fact is we don't say a person with a gun shot wound in his head was 'medicated' or that the subsequent psychosis following the gunshot wound was a pre existing disease.
Chemical addiction can over time cause 'chemical brain damage".  This is what the fMRI studies are showing.  Certainly that was what was first readily evident with 'glue sniffing'. It's been long shown with alcohol.  The DSMIV has the category Substance Disorder and Alcohol dementia is a well recognised consequence of alcohol addiction. Marijuania causes schizophrenia.  It certainly causes psychosis and persistent use results in schizophrenia, which is essentially a term for chronic psychosis. Long before the American models of psychosis adapted the French separated 'brief psychosis' which really were not that predictive of long term mental illness from psychosis that persisted beyond 6 months or a year. Some of the imaging studies of chronic opiate abuse show what appears to be irreversible damage to the 'pleasure zones' of the brain suggesting that a small group of opiate addicts become 'dependent' on opiates much like a person who uses exogenous thyroid medication can cause the thyroid to shut down.  These brain processes can be 'rebooted' in some cases but in others it appears that the condition is permanent.  fMRI studies of cocaine abuse show reversible damage to the frontal lobes, the human brain per se as opposed to the basal brain more associated with reptilian function.    

Addiction is a 'brain disease".  It may start as 'self medication' but in the end it's "iatrogenia' and maybe the term 'self iatrogenia' would be more appropriate. Further people who have no overt illness, so many who would never be diagnosed as having any mental illness go on to develop mental illness and brain disease simply as a consequence of addiction. The addiction is the primary problem and the primary disease.