A1: What are co-occurring conditions?

In these Guidelines, ‘co-occurring conditions’ refers to the co-occurrence of one or more AOD use disorders with one or more mental health conditions. This phenomenon is often referred to as ‘dual diagnosis’; however, this term is often misleading, as many clients present with a range of co-occurring conditions of varying severity [13]. It should be noted that there are other types of co-occurring conditions. For example, a person may have co-occurring AOD use disorders (i.e., more than one AOD use disorder). Indeed, one of the most common and often overlooked co-occurring conditions in AOD clients is tobacco use (discussed in Chapter B1; [14–17]). Other conditions that are often found to co-occur with AOD use disorders are physical health conditions (e.g., cirrhosis, hepatitis, heart disease, diabetes), intellectual and learning disabilities, cognitive impairment, and chronic pain [18–24]. This combination of substance use, mental and physical health conditions is often referred to as ‘multimorbidity’ [25]. While there are a number of different types and possible combinations of co-occurring conditions, these Guidelines focus on the co-occurrence of AOD use disorders and mental health conditions.

To be classified as having a mental disorder, a person must meet a number of diagnostic criteria (see Chapter A4 for a discussion of the classification of mental disorders). There are, however, a large number of people who present to AOD treatment who display symptoms of disorders while not meeting criteria for a diagnosis of a disorder. For example, a person may exhibit depressed mood or anxiety without having a diagnosable depressive or anxiety disorder. Although these people may not meet full diagnostic criteria according to the classification systems, their symptoms may nonetheless impact significantly on their functioning and treatment outcomes [26, 27]. For example, people who report symptoms of depression but do not meet diagnostic criteria may have reduced productivity, increased help-seeking, and an increased risk of attempted suicide [28]. Therefore, rather than viewing mental health as merely the presence or absence of disorder, mental health conditions can be viewed as a continuum ranging from mild symptoms (e.g., mild depression) to severe disorders (e.g., schizophrenia or psychotic/suicidal depression).

In this document we use the term co-occurring ‘mental disorder’ when referring to people with a diagnosable mental disorder, as defined by the DSM [10, 29]. When using the term ‘mental health condition’, we are referring to both people who have a diagnosable disorder as well as people who display symptoms of disorders while not meeting criteria for a diagnosis of a disorder.