Dual Diagnosis: Substance Abuse and the Mentally Ill

In recent years, there has been increasing concern about the problems and clinical management of people with mental illness and substance use disorders, which is referred to as dual diagnosis (DD). Reports of the types of substances preferred by patients with severe mental illness have varied. Studies have reported that individuals diagnosed with schizophrenia are more likely to use "entry-level" substances, such as alcohol and cannabis, than the hard-core street drugs that substance users without mental disorders more typically select. Other investigators have found that individuals given a diagnosis of schizophrenia show a greater preference for drugs that either induce psychotic symptoms or that counteract negative symptoms, such as cocaine, cannabis, amphetamines and hallucinogens, than depressant drugs, such as sedative--hypnotics, opiates and alcohol. The most commonly used substances are those that allow the client to self-medicate uncomfortable neurological symptoms.

Even low level use by individuals with severe mental illness carries considerable risks and has also been shown to be related to adverse clinical outcomes. For example, several studies have reported that people with a dual diagnosis are more likely to be thought-disordered, to experience hallucinations and depression and are more likely to engage in suicidal behavior than individuals with severe mental illness who do not misuse substances. They may also be at increased risk of showing violent behavior towards others. On the other hand, there have also been reports that the combination of schizophrenia and substance misuse is associated with fewer negative symptoms than schizophrenia alone. At present, little is known about the relative long-term adjustment of individuals whose substance use predates the onset of the mental illness, compared with that of people who become mentally ill and then use substances as a means of coping with distressing symptoms.