The dual in Dual diagnosis refers to people who have mental illnesses coexisting with drug addiction or alcohol use. This automatically means that the treatment protocol in use will have to cater to only the primary problem but also to the secondary coexisting problem of possible substance dependence. This is not uncommon and can go both ways. i.e people with mental illness may have substance abuse problems, and people with problematic drug and alcohol use may also experience mental illness.
There also seems to be evidence that the higher the severity of mental illness the higher the chance of using substances i.e. nearly one-third of people with all mental illnesses and approximately one-half of people with severe mental illnesses including bipolar disorder and schizophrenia. Likewise more than a third of all alcohol abusers and more than one-half of all drug abusers also experience mental illness.
Drugs and alcohol can be a form of self-medication to feel less pain. This short term relief can make prognosis poor and extend the length of treatment. Drugs and alcohol can precipitate the onset of symptoms even in people who are not involved before. There is also a higher chance to develop severe medical complications as well as an increased risk for suicide as well as the chance that their suicide attempt is successful.