Co-occurring disorders (CODs), sometimes referred to as dual diagnosis or comorbid diagnoses, occur when a client has both a substance use disorder (SUD) and a mental health diagnosis occurring at the same time. In the past and in some cases even now, the standard treatment for those with COD has been to treat the disorders sequentially; i.e. first one and then the other. More often the individual is treated for both disorders at the same time, but in different locations with different providers. The treatment that has been found most effective is integrated treatment. This involves treating the individual for both disorders in the same location with a team of providers that are trained in both substance use and mental illness.
Co-occurring disorders are widely prevalent. It is estimated that 3 of 10 people with a mental health diagnosis will be diagnosed with an SUD. In clients with an alcohol use disorder, 37% meet criteria for a mental health diagnosis. Sixty-four percent of drug users meet criteria for a mental health diagnosis (Daley & Moss, 2002). When looking at particular risk for lifetime prevalence of SUD by psychiatric diagnosis, schizophrenia and bipolar disorder stand out with rates reaching 47% and 56%, respectively (Mueser, Noordsy, Drake, & Fox, 2003).
To put the relationship between substance use and mental health into better perspective, it is important to note that when a client has a mental health disorder, the odds of also meeting criteria for a SUD range from 23%-56%, while in the general population the rates of SUD diagnosis is around 17% (Regier et al., 1990).