Dopamine release in one area of the brain’s striatum is increased in schizophrenia, whereas drug addiction is associated with decreased dopamine in a neighboring striatal region. Since substance use disorders often occur concurrently with other mental illnesses, such as schizophrenia, a new NIDA-funded study examined amphetamine-induced dopamine release in patients with comorbid schizophrenia and substance dependence. In this study, dopamine release was reduced in the striatum of comorbid patients exposed to amphetamine, yet patients showed enhanced positive symptoms (i.e., psychotic reaction), as previously observed in schizophrenia. These results suggest that these comorbid patients suffer from a combined dysfunction: a) increased dopamine sensitivity in the part of the striatum responsible for the psychotic symptoms and, based on prior research, b) reduced sensitivity to dopamine in the area of the striatum associated with reward. Such a set of alterations in dopamine release could set up a vicious cycle of using drugs to self-medicate, which in turn may cause or further worsen psychosis.
Better understanding of the brain changes underlying comorbid disorders could lead to improved treatments for both drug addiction and schizophrenia in patients possessing both disorders. This is a vital research area, since failure to treat co-occurring conditions can jeopardize a patient’s chance of recovery.
–National Institute of Drug Abuse