Treating depression in patients with alcohol or drug use disorders: A need for clearer guidelines

Depressive symptoms are widespread among patients seeking help with an alcohol or other drug use disorder. As most drugs of abuse have immediate, direct biological effects on mood, it can be extremely challenging to determine whether the depression represents an independent disorder or is substance-induced, particularly in the context of ongoing substance use. Furthermore, in contrast to the substance-specific mood effects seen during intoxication and withdrawal, depressive symptoms are common in long-term heavy users of virtually all drugs of abuse, including nicotine and alcohol. Experiencing such symptoms can also be an effect of struggling to cope with major psychosocial stressors, which ongoing drug use may further exacerbate. As such, even in patients whose depressive symptoms occur only after heavy substance use, it is often unclear if this relates to direct biological effects, social problems and/or lifestyle factors caused by their substance use. For example, stimulant use often promotes a lifestyle which disrupts diurnal rhythms, affects diet and impairs physical health, while heavy use of any substance can impact upon work and relationships. In other cases, the presence of depression may promote substance use as a way of trying to cope with dysphoria, poor sleep or anxiety. Finally, substance use disorders and mood disorders share overlapping genetic and environmental aetiologies. For any individual, more than one causal mechanism may be present, and the contribution of each mechanism to the current presentation may vary over time. Co-occurring problems such as personality disorders and posttraumatic stress disorder are common among patients with substance use disorders, and these may also contribute to mood symptoms, further complicating the picture. The Feighner criteria of the early 1970s promoted a categorical approach to diagnosis, labelling mood disorders as primary or secondary according to whether another preexisting condition explained the mood disorder. This schema strongly influenced later editions of the Diagnostic and Statistical Manual of Mental Disorders (DSM) and International Classification of Diseases (ICD). DSM-5 and the draft version of ICD11 both still recognise substanceinduced mood disorders as diagnostic categories. They note that substanceinduced depression (SID) resembles other forms of depression in its symptom profile, but differs only insofar as symptoms are judged to be a direct consequence of substance use. DSM and ICD take similar approaches to determining whether a mood disorder is substance-induced. Both systems focus on determining the temporal relationship between substance use and depression to make a diagnosis of SID, and they essentially frame SID as a diagnosis of exclusion. DSM does this by defining independent depression (ID), which is mutually exclusive with SID. ID is diagnosed when there is a history of depression preceding the onset of substance use, or at least 1 month after the cessation of acute withdrawal or severe intoxication. While intuitively appealing, identifying a history of ID requires patients to recall accurately the temporal relationship between past mood problems and substance use. This procedure is prone to bias, therefore the reliability of a diagnosis of ID or SID is often low. Despite substance use disorders being prevalent in Australia and New Zealand, population surveys find SID difficult to detect. For example, the lifetime prevalence of substanceinduced mood disorders was only 0.1% in a recent study in Australian men, compared to 18.2% for mood disorders in total (Williams et al., 2016). This suggests current procedures to identify SID do not work well in population settings. In substance treatment settings, it is easier to identify patients who appear to have SID, but follow-up studies show that over time many of these patients are re-categorised as having ID. The Royal Australian and New Zealand College of Psychiatrists (RANZCP) clinical practice guidelines for mood disorders note the importance of assessing substance use in Treating depression in patients with alcohol or drug use disorders: A need for clearer guidelines