Schizophrenia is a severe psychiatric disorder that affects approximately 1% of the general population.1 The 12-month prevalence of substance use disorders (SUDs) among the general US population is approximately 12% for alcohol and 2% to 3% for illicit drugs.  It is interesting to note that nearly 50% of people with schizophrenia also suffer from a comorbid substance-related illness during their lifetime.  There are complex interactions between substance use and psychiatric disorders, including schizophrenia.

Patients who receive a dual diagnosis—a psychiatric disorder and an SUD—are faced with serious challenges related to treatment and prognosis. Many clinicians focus solely on treating either the psychiatric illness or the SUD. This lack of integration of psychiatric and addiction treatment is a significant issue for dual-diagnosis patients; growing evidence suggests a poorer prognosis with nonintegrated treatment.

Psychiatric illness appears to be a vulnerability factor for substance abuse, and because substance abuse can lead to an exacerbation of psychiatric symptoms, there is a critical need to understand the factors that influence both the onset and duration of substance abuse and psychiatric illness, particularly how they interact to influence prognosis.

Conclusions 

Identifying reasons for comorbid drug addiction in schizophrenia has been difficult. Many theories have been proposed to try to explain the root cause of drug addiction in patients with schizophrenia, but no one theory has been put forth that encompasses all aspects of drug addiction in these patients. The SMH falls short by assuming that drug addiction in schizophrenia operates on a negative reinforcement model.   Nonetheless, it is clear that the prognosis for schizophrenia is much better when patients achieve drug abstinence, including in the domains of depression, quality of life, and community integration.

Clearly, more research on the interrelationships between substance use disorders and schizophrenia is needed to support or refute the SMH or the AVH—and to establish the sequence of onset of the comorbid disorders. In other words, which came first, the chicken or egg? The answer to this question may have important implications for how we assess and treat people with drug addiction and schizophrenia.

Source:  http://www.psychiatrictimes.com/schizophrenia/understanding-neurobiological-basis-drug-abuse-comorbidity-schizophrenia/page/0/3?GUID=8CCBBF2C-6541-4A09-A30A-3E72BFE8C975&rememberme=1&ts=01102013#sthash.VXFBioNs.dpuf   February 12, 2013