The literature suggests that nearly 50% of patients with schizophrenia have a co-occurring substance use disorder (SUD), most frequently alcohol and/or cannabis (at a rate about three times as high as that of the general population). Outcomes associated with Comorbid SUD and Schizophrenia are earlier onset of schizophrenia, increased relapses, treatment noncompliance/more side effects, poorer response to antipsychotic medication, more hospitalizations, increased risk for violence, increased medical costs, more affective disturbance. These conditions are also associated with increased suicide risk. The increased suicide risk of substance abusing schizophrenic patients could be the result of a cumulative effect of many factors or events, such as the loss of remaining social control through the consumption of psychotropic substances, noncompliance with antipsychotic medication, presence of paranoia and depression.

Abuse substances worsen both symptoms and prognosis of the illness and are related to higherrelapse rates.

Studies suggest that some of the second-generation (atypical) agents may be helpful for these patients. Some researchers have suggested that the lower incidence of neurologic side effects produced by the atypical antipsychotics, along with the possibility that these agents may be more likely to decrease negative symptoms, make them a logical choice for patients with co-occurring substance use disorder (even though parameters of the metabolic syndrome must be monitored while using these agents).