When someone has both a drug or alcohol addiction and a mental health diagnosis or psychiatric issue, they are considered to fit into a category called dual diagnosis. For instance, someone might have both bipolar disorder and alcohol dependence. Another example might be someone who has both major depression and engages in ecstasy abuse.

Being dually diagnosed makes treatment more difficult because both the issue of addiction and the problems associated with the mental illness must be addressed at the same time. According to the Journal of Clinical Psychiatry, people who have depression or anxiety are about twice as likely as the general population to have a drug-related issue. The most common mental health issues associated with dual diagnosis are:

• Personality Disorders (such as Antisocial Personality Disorder)
• Mood Disorders (such as Feelings of Depression or Bipolar Disorder)
• Schizophrenia
• Anxiety Disorders (such as Generalized Anxiety Disorder or Panic Attacks)

How does a dual diagnosis develop?
There is no way to know whether mental illness or substance issues develop first. Mental illness may increase the likelihood that someone starts abusing substances. Or the opposite may be true—abusing substances may lead people to develop mental illness. A third possibility is that both appear around the same time, and neither causes the other.

Although researchers are unsure which develops first, they have several theories about what causes dual diagnosis. The first is that mental illness and substance abuse may have genetic overlap. The same genes may possibly play a role in both categories of disorders. Another theory is that stressful childhood environments may be fertile ground for the growth of both substance and mental health issues. For instance, if someone was sexually abused as a child, they may be more vulnerable to the development of a variety of disorders. The third theory is a brain-based one. There may be overlapping areas of the brain that control both emotional functioning and response to using substances. Finally, some speculate that the root of dual diagnosis may be developmental. Often both mental illness and substance abuse emerge during adolescence.