Comorbid mental disorders and substance use disorders: epidemiology, prevention and treatment

Implications of comorbidity for management

Page last updated: 2003

Interventions for substance use disorders for those with mental disorders need to take account of several key features of comorbidity, many of which are reviewed more extensively in previous chapters. These include:

  1. Frequencies are high. Comorbidity between substance use and other mental disorders is very common (Degenhardt, Hall, & Lynskey, 2001; Regier et al., 1990), especially in higher intensity treatment settings (Kavanagh, Saunders et al., 1999), and it often involves multiple substances (Degenhardt et al., 2001; Kavanagh et al., 2002). Predictive factors for comorbidity (especially in relation to illegal drugs) are similar to those in the general community, including male gender, young age, lower educational level, and single (or divorced) marital status (Burns & Teesson, 2002; Mueser, Noordsy, Fox, & Wolfe, 2000; Salyers & Mueser, 2001).

  2. Highest risk vs. highest frequency produce different target groups. The greatest numbers of people with this comorbidity in the population are those with the most commonly occurring disorders — i.e. anxiety or depression, and misuse of alcohol or nicotine (Degenhardt et al., 2001). On the other hand, the greatest increased risk in Axis I disorders is seen in psychoses (Regier et al., 1990), and these people are also more likely to show significant functional deficits from substance use, even at relatively low levels of intake (Drake, Osher, & Wallach, 1989; Drake & Wallach, 1993).

  3. The greatest health impact is from cigarette smoking. Smoking-related diseases represent a critical source of excess morbidity and early mortality in mental disorders, especially in people with schizophrenia (Brown, Inskip, & Barraclough, 2000; Lichtermann, Ekelund, Pukkala, Tanskanen, & Lonnqvist, 2001), for whom the rates of cigarette smoking are very high (Reichler, Baker, Lewin, & Carr, 2001). However smoking has been relatively neglected in the development of specific management approaches for people with comorbid mental disorders.

  4. Higher rates of comorbidity are found in more intensive treatment settings. Patients with either substance use or mental disorders who are receiving emergency or inpatient treatment are likely to show very high rates of comorbidity, partly because of what has become known as Berkson's bias (Berkson, 1946). The joint symptomatic and functional impacts from both disorders increases the chance that the person will receive treatment (Mueser et al., 1990). If patients from populations with exceptionally high risk are examined — such as hospitalised young people with psychosis — a substantial majority may have comorbid substance use disorders (Galanter & Castaneda, 1988; D. J. Kavanagh et al., 1999).

  5. Correlates may differ across substances. While many correlates of substance use disorders in clinical populations closely parallel those in the general population (Salyers & Mueser, 2001), there is also evidence that the pattern of correlates differs across substances (Mueser, Bellack, & Blanchard, 1992; Mueser et al., 1990). For example, young people with psychosis are especially prone to abuse of cannabis, cocaine, and amphetamines, whereas alcohol use disorders tend to occur more over the life span.

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  6. Comorbidity results in poorer physical and psychiatric outcomes. Comorbidity of substance use and severe mental disorders is associated with an increased risk of illness and injury (Dickey, Azeni, Weiss, & Sederer, 2000), including self-harm and suicide (Allebeck & Allgulander, 1990), and poorer psychiatric outcomes (Mueser et al., 1992).Treatment is often less effective (Worthington et al., 1996) and the risk and severity of significant medication side-effects are increased in clients with substance misuse (Dixon, Weiden, Haas, Sweeney, & Frances, 1992; Zaretsky, Rector, Seeman, & Fornazzari, 1993). Among the contributors to increased relapse rates and reduced treatment effects is a reduced rate of medication adherence and appointment attendance (Owen, Fischer, Booth, & Cuffel, 1996). Assertive follow-up is rendered more difficult by increased rates of mobility and homelessness (Mueser et al., 1992), and the engagement and retention in treatment for comorbidity is often a significant challenge.

  7. A variety of causal relationships may apply. In some cases, the management of one disorder may result in recovery from the other. For example, in Brown and Schuckit (1988), 42% of people entering inpatient alcohol dependence treatment had a depressive syndrome, but after four weeks of abstinence only 6% were clinically depressed. The reverse is less often true, although the pharmacological treatment of comorbid depression together with an alcohol intervention may sometimes produce improved alcohol outcomes in comparison with a placebo plus alcohol treatment (Cornelius, Salloum Ihsan, Ehler, & Jarrett, 1997). However comorbid disorders often appear to be in a relationship of mutual influence rather than falling neatly into primary vs. secondary categories (Mueser, Drake, & Wallach, 1998), and the relationship between disorders may change over time e.g., depression may trigger alcohol use at some times and the reverse may occur at others (Hodgkins, el-Guebaly, Armstrong, & Dufour, 1999).

  8. Different intervention structures may be necessary in different subgroups. A relationship of mutual influence implies that comorbidity will often be best treated in a fully integrated manner, and this does appear to be the case in people with psychosis and Substance use Disorder (SUD) (Drake, Mercer-McFadden, Mueser, McHugo, & Bond, 1998).The situation is less clear with anxiety or depression comorbid with substance misuse at this time (Oei & Loveday, 1997; Scott, Gilvarry, & Farrell, 1998).

  9. Comorbidity is under-serviced. One UK survey estimated that even for psychosis and SUD, only 20% of people were offered substance misuse interventions and only 5% were compliant (Weaver et al., 2001). Part of the problem is that many people with comorbidity are not identified because of a lack of systematic screening (Appleby, Dyson, Luchins, & Cohen, 1997). This is discussed in greater detail in Chapter 6. Another issue is that people with comorbidity are sometimes excluded from services that might otherwise assist them (D. J. Kavanagh et al., 2000). In another sense, people with comorbid substance and mental health disorders are not under-serviced; they tend to be higher users of emergency, inpatient and intensive treatment services than people without comorbidity, because of their poorer outcomes (Bartels et al., 1993).
Several implications follow from these points. Firstly, the very large group of people in the community with the most common disorders presents different challenges for service delivery than the groups that form the majority of the people being seen by current treatment services. The former will require relatively inexpensive, highly accessible interventions that focus particularly on anxiety or depression and alcohol, nicotine and cannabis. The latter will demand interventions that can meet the needs of people with severe disorders and that may often be more intensive. Within services there will also be differing needs and emphases. Alcohol and drug services are likely to see people with more severe substance use disorders (especially substance dependence), while mental health services will more often see people with less common but more severe mental health problems such as psychoses (Primm et al., 2000). People with different substance use problems may have differing characteristics from each other, and may even sometimes form different sub-cultural groups.

Collectively, these issues pose considerable demands on interventions for comorbidity. The high comorbidity rates, especially within intensive treatment services or population subgroups at very high risk, highlight the need for the delivery of sound comorbidity interventions to be core business for health services; and facility in their delivery to be a core skill of practitioners in specialist mental health or substance use disorder services. Without these skills, many people will continue to miss receiving appropriate treatment, and will continue to both have poor outcomes and to be disproportionately represented among the users of emergency and other high-cost services. On the other hand, the high population numbers suggest that comorbidity of substance use and mental disorders also needs to be a priority for primary care.

The complex social and legal issues that often arise in connection with comorbidity and the increased risks of serious illness, suicide and symptomatic relapse imply that interventions to address these multiple problems will often be necessary. At the same time, the difficulties often experienced in engagement and retention in treatment and the increased mobility of the more severely affected patients pose a significant challenge for treatment agents.Top of page

Overall, it seems that a set of interventions may be required rather than a single intervention format. We will try to encompass this diversity in the remainder of this chapter, but will necessarily not do equal justice to all of the possible intervention variants.