Many individuals who struggle with a substance use disorder may have a co-occurring mental health disorder. When two disorders coexist, it is referred to as a dual diagnosis. The existence of a dual diagnosis creates a more enhanced, even erratic, overall version of a substance use disorder. This is because the substance abuse exacerbates the symptoms of the mental health issue, and the mental health disorder can lead to increased dependence on a substance to manage the symptoms. This creates a revolving cycle where one disorder augments the effects of the other, which introduces a more complex clinical treatment challenge.

There is no agreement yet in the mental health profession regarding the significance behind the primary disorder, whether it is the substance use disorder or the mental health disorder. The co-occurring disorders can originate either way. For example, someone with depression may rely on alcohol to help mask the emotional pain of the depression. Eventually the alcohol use escalates and becomes the secondary condition, alcohol use disorder. On the other hand, someone with an alcohol addiction may begin to experience the destructive consequences of the disorder, which can result in depression.