Over the course of their lifetime, approximately half of all people with schizophrenia will have a co-occurring substance use disorder [SUD] (Havassy et al., 2004). According to the Epidemiologic Catchment Area Study and the National Comorbidity Survey, these rates are significantly higher in people with severe mental illness such as schizophrenia than in the general population (Kessler et al., 1994; Regier et al., 1990). Alcohol, cannabis, and to a lesser extent, cocaine and amphetamine are the most frequently abused substances in people with schizophrenia, with regional variation on use patterns (Cantor-Graae et al., 2001; Drake et al., 1996; Mueser et al., 1990; Siris et al., 1988). The reported rates of alcohol use is 20% to 60%, cannabis use from 12% to 42%, cocaine use from 15% to 50% (Chambers et al., 2001) and amphetamine use from 10% to 25% (Littrell et al., 2001; Mueser et al., 1990; Siris et al., 1988) in people with schizophrenia. The use of more than two drugs at the same time is also common (Soyka et al., 1993). Other drugs of abuse in this population
