Co-occurring severe mental illness, usually schizophrenia or bipolar affective disorder, and substance misuse is termed dual diagnosis. Mental illness and its consequences may lead to substance misuse as a coping strategy. Substance misuse can lead to mental health problems, either by triggering a first episode in a susceptible person, or by exacerbating an existing disorder. However, substance misuse itself is unlikely to be the sole cause of a severe and enduring mental illness.