Alcohol-related psychiatric comorbidity

Background Alcohol problems and common mental disorders, particularly depression, contribute greatly to the global burden of disease and they often coexist. However, many aspects of the relationship between these two groups of health conditions are incompletely understood. Aims The aims of the thesis fall into two groups. The first group of investigations focuses on the association between alcohol use and psychological distress, a proxy marker for mental illness, in the New Zealand population. These investigations have five main aims: i. To replicate the previously-described J-shaped relationship between alcohol use and psychological distress in the population. ii. To assess whether there is an elevated risk of high psychological distress among hazardous drinkers in general, or only people with more severe forms of hazardous drinking. iii. To investigate whether measures of alcohol consumption or alcohol problems are better predictors of high psychological distress. iv. To investigate gender differences in the relationship between alcohol use and psychological distress. v. To examine other sociodemographic variables that may confound or mediate the relationship between alcohol use and psychological distress. The second group of investigations focuses on predicting the outcome of depressive symptoms among treatment-seeking individuals with an alcohol use disorder. These investigations have a further five primary aims: i. To compare treatment outcomes for patients with independent depression and those with substance-induced depression. ii. To describe the trajectory of depression following treatment in these patients. iii. To determine whether the effect of antidepressant therapy differs between independent and substance-induced depression. iv. To identify other patient and treatment-related variables associated with depression outcomes. v. To investigate the extent to which changes in drinking are associated with depression outcomes, and to assess whether this varies according to whether depression is independent or substance-induced. Design The thesis is in two parts. The first part considers population data and the second part concerns data from treatment-seeking samples. Part one comprises a secondary analysis of data from a household survey, the New Zealand Health Survey 2006/07. Patterns of association between alcohol measures taken from the Alcohol Use Disorders Identification Test (AUDIT) and psychological distress are investigated. In particular, the three alcohol consumption items and the seven alcohol problems items from the AUDIT are compared as predictors of high psychological distress. High psychological distress, defined as a score of 12 or more on the K10 scale, is used as a proxy measure of the risk of serious mental illness. Part two concentrates on treatment-seeking depressed patients with a coexisting alcohol use disorder. This section comprises a systematic review and meta-analysis of clinical trial data, followed by analysis of data from the Treatment Evaluation of Alcohol and Mood (TEAM) study, a multi-centre randomised controlled trial conducted in New Zealand. Predictors of the trajectory of depression in treatment are investigated. In particular, the utility of categorizing depression as independent or substance-induced, the role of personality variables, and the efficacy of antidepressant therapy are examined. Findings The previously described J-shaped relationship between alcohol use and high psychological distress was replicated. Adjustment for potential confounders resulted in flattening of the J-shaped curve but in multivariate models elevated levels of distress remained among both abstainers and those with high AUDIT scores. Milder forms of hazardous drinking were associated with a modestly increased risk of high psychological distress compared to moderate drinking, but the risk of high distress increased steeply among those with the highest AUDIT scores. Alcohol-related problems predicted high distress more strongly than alcohol consumption measures. The association between alcohol use and psychological distress was similar for male and female heavy drinkers. However, male but not female abstainers had an increased adjusted risk of high distress compared to moderate drinkers. Socioeconomic status variables were important confounders of the relationship between alcohol and psychological distress. In clinical samples of depressed patients with an alcohol use disorder, evidence from a systematic review and meta-analysis provided little evidence that independent depression and substance-induced depression have a different trajectory in treatment. Antidepressant therapy had at most a small effect in the studies on patients with independent depression. The standardised mean difference in Hamilton Depression Rating Scale score after treatment was 0.25 (95% CI 0.06, 0.44) between placebo and antidepressant groups. Outcomes in the remainder of studies, in which depressive symptoms were less clearly defined, showed high heterogeneity and the pooled standardised mean difference was 0.08 (95% CI -0.35, 0.51). In the TEAM study, neither patients with independent or substance-induced depression responded to antidepressant therapy, but patients with substance-induced depression had modestly better outcomes for both depression and drinking. Personality variables were among the strongest predictors of depression outcomes in the TEAM study. In particular, high self-directedness and high cooperativeness, which are markers of good global personality functioning, were associated with better outcomes. Low harm avoidance, a marker of low trait anxiety, was also associated with more improvement in depression. Reduced drinking was associated with improvement in depression for all patients, not just those with independent depression. Conclusions In the New Zealand population, harmful drinking is associated with an elevated risk of high psychological distress. This appears to be more strongly related to alcohol problems rather than alcohol consumption per se, suggesting the effect of alcohol use on mental health may be mediated by alcohol problems. Better understanding of the role of socioeconomic status as a causative factor in alcohol-related psychiatric comorbidity is also needed, as this would help inform prevention strategies and service delivery. In clinical samples of depressed patients with an alcohol use disorder, comprehensive psychosocial treatment and reduced drinking is associated with a large and rapid improvement in both drinking and depression for most patients. A significant minority of depressed patients with an alcohol use disorder do not show improvement, and assessing personality functioning at baseline may help to identify this group of patients and tailor service delivery for them. There is little evidence that patients with substance-induced depression from heavy drinking have more rapid or greater overall improvement than those with independent depression. Antidepressant therapy has at most a modest effect on depression in patients with an alcohol use disorder, with the most consistent evidence being in more independent forms of depression