How common is comorbidity among clients of AOD treatment services?

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Comorbidity among clients of AOD treatment services is not a new phenomenon: AOD workers have been responding effectively to comorbidity for many years with very little guidance from the research field. There has, however, been an increase in awareness of this phenomenon due to the development of structured diagnostic interviews, and their use in large-scale population surveys [18, 60]. The high prevalence of comorbid mental health disorders among individuals with AOD use disorders in the Australian general population was highlighted by the 2007 NSMHWB (see Table 1). These estimates indicate that 35% of individuals with a substance use disorder (31% of men and 44% of women) have at least one co-occurring affective or anxiety disorder, representing nearly 300,000 Australians. Furthermore, of the 183,900 Australians who used alcohol or other drugs nearly every day, 63% had a 12-month mental disorder [61]. The prevalence of comorbidity is even higher among individuals entering AOD treatment programs, because the presence of co-occurring disorders increases the likelihood of treatment seeking [62-64].

A variety of mental health disorders have been found to co-occur in clients of Australian AOD services. Studies that have undertaken comprehensive assessments of mental health disorders indicate that between 50–76% of Australian clients meet diagnostic criteria for at least one comorbid mental disorder [65-67]. At least one in three have multiple comorbidities [65, 66, 68]. The proportion of clients who have a mental disorder documented in their medical records, however, ranges from 42–52% [68-71], indicating that a number of cases likely go unrecognised.

Table 1: Prevalence (%) of mental health disorders in the past year among adults with substance use disorders in the 2007 National Survey of Mental Health and Wellbeing

Disorder % Men % Women % Total
Affective Disorders
Major depressive disorder 16.1 20.3 17.4
Dysthmia 7.5 7.9 7.6
Bipolar affective disorder 3.9 5.1 4.3
Any affective disorder 19.1 22.0 20.0
Anxiety disorders
Generalised anxiety disorder (GAD) 11.5 10.7 11.3
Social phobia 10.9 14.7 12.1
Post traumatic stress disorder (PTSD) 9.3 19.8 12.6
Panic disorder (with or without agoraphobia) 6.6 4.1 5.8
Obsessive compulsive disorder (OCD) 9.1 10.2 9.5
Agoraphobia (without panic disorder) 2.3 4.7 3.1
Any anxiety disorder 28.1 38.5 31.4
Any disorder (affective/anxiety) 31.1 44.0 35.2

As in the general population, the most frequently seen disorders among people seeking AOD treatment are anxiety disorders (45–70%), most commonly GAD [65, 66, 72, 73]; depression (26–60%) [65-67, 70, 73-76], PTSD (27–51%) [65, 67, 74, 76]; and personality disorders, in particular, borderline personality disorder (BPD) (37–66%) [76] and ASPD (61–72%) [72, 76]. Although less common, studies have also found elevated rates of bipolar disorders (4–10%) [65, 67]; psychotic disorders (2–10%) [65, 68-71]; obsessive-compulsive disorder (OCD) (1–10%) [65, 67]; ADHD (6%) [70]; and ED (2–9%) [68, 69].

A recent Australian study found that 82% of those in current residential rehabilitation had experienced an anxiety disorder in their lifetime (70% were experiencing a current anxiety disorder), and just over 79% had experienced depression in their lifetime (55% were experiencing current depression) [73]. Similarly, rates of trauma exposure and PTSD have been shown to be extremely high across a number of settings [74, 77, 78].

It should be borne in mind that the prevalence of mental health disorders may vary between substances. Little research has been conducted comparing the rates of mental health disorders across different types of AOD use disorders; however, there is some evidence to suggest that co-occurring disorders are higher among those who use stimulants and opioids [64]. For example, the prevalence of PTSD is much higher among individuals with opioid, sedative, or amphetamine use disorders compared to those with alcohol or cannabis use disorders [79].

The number of potential combinations of disorders and symptoms is infinite. Furthermore, as mentioned in Chapter A1, there are 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 [80]. Individuals who display a number of symptoms of a disorder but do not meet criteria for a diagnosis are sometimes referred to as having a ‘subsyndromal’ or ‘partial’ disorder. Although these individuals may not meet full diagnostic criteria according to the classification systems (described in Chapter A4), their symptoms may nonetheless impact significantly on their functioning and treatment outcomes [21, 81-84].