Persons with
schizophrenia are at a high risk, almost 4.6 times more likely, of having
drug abuse problems than persons without
psychiatric illness. Among the influential proposals to explain such a high comorbidity rate, the '
self-medication hypothesis' proposed that persons with
schizophrenia take to drugs in an effort to cope with the illness and medication side effects. In support of the
self-medication hypothesis, data from our earlier clinical study confirmed the strong association between
neuroleptic dysphoria and negative subjective responses and comorbid
drug abuse. Though
dopamine has been consistently suspected as one of the major culprits for the development of
neuroleptic dysphoria, it is only recently our neuroimaging studies correlated the emergence of
neuroleptic dysphoria to the low level of striatal
dopamine functioning. Similarly, more evidence has recently emerged linking low striatal
dopamine with the development of vulnerability for
drug addictive states in
schizophrenia. The convergence of evidence from both the dysphoria and comorbidity research, implicating the role of low striatal
dopamine in both conditions, has led us to propose that the person with
schizophrenia who develops dysphoria and comorbid addictive disorder is likely to be one and the same.