Substance abuse and psychopathology frequently co-occur in the general population and in mental health and substance abuse treatment settings. In the general population, individuals with mental illness are 2. 7 times more likely than those without to have a substance use disorder. In addition, those with a substance use disorder, especially drugs other than alcohol, are 4.5 times more likely to be mentally i11. 1 ,2

In mental health treatment settings, the strong association between substance abuse and psychopathology is also well documented.3'4 In a study of 435 admissions to two inner-city psychiatric hospitals, Lehman et al. found that the lifetime prevalence of substance abuse was over 70 percent and the current prevalence over 50 percent.4 Studies of the prevalence of psychopathology among substance abusers in treatment document similarly high lifetime prevalence rates for opioid addicts (86.9 percent), cocaine addicts (70.1 f.ercent), and alcohol and other drug-addicted persons (84.2 percent). ,6

Despite the extensive documentation of the frequent co-occurrence of substance abuse and psychopathology, our understanding ofthese so-called "dually diagnosed" individuals remains limited. Weiss and Collins 7 discuss the complexity of the relationship

betweensubstanceabuseandpsychopathology,anddescribefive differentwaystoviewit.