In the past, there has been a focus on establishing the order of onset of conditions to identify which is the primary disorder. Conditions may occur in any order, or they may develop at the same time. The evidence regarding the typical order of onset of disorders is not consistent, and differences have been observed between males and females [63, 64]. It appears, however, that social anxiety disorder (SAD), specific phobia, and post traumatic stress disorder (PTSD) tend to predate the AOD use disorder in most – but not all – cases, whereas generalised anxiety disorder (GAD), panic disorder, depression, and dysthymia, tend to have their onset after the onset of an AOD use disorder [63, 65].
Establishing the order of onset of conditions can be useful in understanding the relationship between conditions, and in developing a case formulation (see Chapter B3). It is important to note, however, that once co-occurring conditions have been established it is most likely that the relationship between them is one of mutual influence rather than there being a clear causal pathway [65, 66] (see Figure 3). Regardless of how the co-occurrence came about, both conditions may serve to maintain or exacerbate each other. For example, a person may engage in AOD use to reduce symptoms of depression; however, research suggests that repeated use may lead to increased depression [33]. It is also possible that the relationship between disorders may change over time [66, 67]. For example, depression may trigger alcohol use on some occasions, while it may be the result of alcohol use on others [68]. Irrespective of what order co-occurring conditions have developed, the strategies used to manage these conditions are the same.
Figure 3: Example of a relationship of mutual influence between AOD use and mental health conditions