Dual diagnosis is a condition in which clients have been diagnosed as having both a mental health disorder and a substance use disorder, as discussed in the Diagnosis and Statistics Manual of Mental Disorders (DSM). The term co-occurring disorders has recently replaced the terms dual diagnosis and dual disorders in an effort to better describe the existence of a mental health disorder and substance use disorder as opposed to a combination of presenting mental health disorders. According to the Substance Abuse and Mental Health Services Administration, a co-occurring diagnosis refers to the coexistence of both a mental health issue and a substance use disorder that are a result of something other than a cluster of symptoms from an existing disorder.

In 2014, 7.9 million adults in ...