How common are co-occurring mental disorders among clients of AOD treatment services?

General population estimates indicate that 35% of Australians with a substance use disorder (31% of men and 44% of women) have at least one co-occurring mood/affective or anxiety disorder (see Figure 5), but this rate is even higher among people entering AOD treatment programs. Although reported rates vary across studies, it is estimated that at least 47% of people seeking AOD treatment have a current mental disorder [76], and at least one in three have multiple co-occurring conditions [77–81]. Thus, in many service settings, co-occurring mental disorders are the norm rather than the exception.

The most frequently seen mental disorders among people seeking AOD treatment mirror those observed in the general population. Although estimates vary substantially between studies depending on the methods and timeframes used to assess for conditions, the most common are anxiety disorders (12 – 91%), most commonly GAD (1 – 75%); depression (27 – 85%); PTSD (5 – 66%); and personality disorders, in particular ASPD (2 – 72%) and borderline personality disorder (BPD; 16 – 48%); bipolar disorders (4 – 53%); obsessive-compulsive disorder (OCD; 1 – 52%); and psychotic disorders (2 – 41%) [76, 81–83]. Although less common, studies have also found elevated rates of eating disorders (ED; 2 - 34%), and attention-deficit/hyperactivity disorder (ADHD; 2 - 6%) [76, 83]. Despite these high rates, these conditions often go unrecognised. It should also be borne in mind that the prevalence of mental disorders may vary between substances, however, little research has been conducted comparing the rates of mental disorders across different types of AOD use disorders [76].

GAD = generalised anxiety disorder; PTSD = post traumatic stress disorder; panic disorder (with or without agoraphobia); OCD = obsessive compulsive disorder; agoraphobia (without panic disorder).

The number of potential combinations of disorders and symptoms is also 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 [84, 85]. People 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 people 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 [84, 86–89].