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

How would you prevent and treat comorbidity?

Page last updated: 2003

As with physical disorders, health care has always been, and will continue to be rationed, and there will never be sufficient funds to provide the care that all individuals with mental disorders need or would like. The UK spends 6.5%, Australia spends 8.5% and Canada spends 9.5% of their respective GDPs on health. Australia spends 5% of the health budget on mental health services (Andrews, Issakidis, & Carter, 2001).Yet, the burden to society of mental disorders and substance use disorders is considerably more than would be implied by this allocation to mental health care. The recent WHO Burden of Disease Report estimates that mental health and drug and alcohol contribute 20% to the burden of disease in society (Murray & Lopez, 1996). Mental disorders are the third leading cause of burden in the developed countries after cardiovascular disease and neoplasms. Within the mental disorders, anxiety and depression account for 56% of the overall burden and substance use disorders account for 23%.

In all, 0.4% of the gross domestic product is spent on mental health and drug and alcohol in Australia. This is half of what Canada, the UK and New Zealand spend. We currently spend a considerable proportion of our health budget on people with chronic long-term disorders. While we have evidence that treatment for mental disorders can be effective (Issakidis, Sanderson,Teesson, Johnston, & Buhrich, 1999), there are substantial numbers of people disabled by mental disorders who do not get treatment and who also may benefit. Importantly, these disorders are amenable to care.

The epidemiology also demonstrates that comorbidity is of particular concern for young adults aged 15–24 years. The recent Australian burden of disease and injury study found that nine out of the ten leading causes of burden in young males, and eight out of ten leading causes in young females were substance use disorders or mental disorders (Table 1). Thus, apart from the burden resulting from road traffic accidents (and asthma in females), the disease burden in this group is the result of alcohol dependence, suicide, bipolar affective disorder, heroin dependence, schizophrenia, depression, social phobia, borderline personality disorder, generalised anxiety disorder and eating disorders (Mathers & Vos, 1999). Comorbidity of these disorders is high with over 50% having comorbid disorders.

This high concentration of mental illness in the young suggests that early intervention and prevention may assist to reduce the burden of mental disorders and, in particular, those that may arise from pre-existing disorders resulting in comorbidity. Prevention is a crucial component in the breadth of interventions considered in the area of comorbidity. A report from the American Institute of Medicine noted that prevention of mental disorders has a low priority in the health care agendas of most countries (Mrazek & Haggerty, 1994). The report suggests that a greater emphasis should be placed on prevention in mental health. The authors argue that several factors make this possible. Firstly there has been a substantial growth in the knowledge about both environmental and genetic risk factors for mental disorders and substance use disorders. Secondly, a number of promising models for early intervention now exist.Top of page

One prevention opportunity, which is fairly unique to mental health, builds on comorbidity. The large US epidemiological studies identified more than 80% of all severe current psychiatric disorders in the USA among the 13% of the population who have a lifetime history of three or more disorders (Kessler et al, 1994). These results suggest that the prevention of comorbidity (ie. prevention of the first onset of a second disorder) might reduce a proportion of lifetime mental disorders or substance use disorders. Thus the epidemiological data suggests that prevention of comorbidity would reduce a substantial proportion of all lifetime psychiatric disorders and an even greater proportion of ongoing disorders.Yet despite such evidence, comorbidity has been largely ignored in risk factor research.

Although some comorbidities would be difficult to prevent, there are others for which successful prevention is a plausible possibility. An example is substance use disorders that occur secondary to primary phobias. There are a number of clinical trials which highlight this comorbidity, with phobias almost always preceding substance abuse in age of onset. This comorbidity is often conceptualised in terms of self-medication or at least use of alcohol and drugs to manage fear. Based on this work, interventions might be aimed either at curing the phobia before secondary alcohol and drug use begins or at teaching alternative strategies to manage fears. Such interventions may have the potential to reduce a substantial percent of lifetime substance use disorders and an even greater percent of current disorders.

Similarly, prevention programs introduced in childhood and adolescence have shown potential to reduce the onset of disorders on follow-up. Research has shown that prevention of anxiety disorders is a reasonable possibility (e.g. Dadds et al., 1999). Therefore, it is also a possibility that such reduction in anxiety disorders may also result in a reduction in the initiation of substance taking. The Dadds study found that for children who were already highly anxious, the program succeeded in reducing the onset of disorder. However, whether programs can prevent anxiety more broadly is still to be demonstrated.

While prevention is crucial, so too is investing in treatments that work. It is a truism that we benefit from knowing what works.That psychological treatments (undefined) benefit the majority of patients (undefined) is already well established. There are three major types of evidence we must examine (Chambless & Hollon, 1998): Efficacy is proven when clearly specified interventions have been shown to be beneficial in controlled research with a delineated population. A treatment manual or equivalent must be available and used, the results replicated and valid outcome measures and appropriate data analysis conducted. An effective intervention is a specific intervention which, when used under ordinary clinical circumstances, does what it is intended to do. Effectiveness studies answer the question "is the intervention effective in applied clinical settings and, if so, with what patients and under what circumstances?" Finally, cost effectiveness determines the economic benefit of an intervention.

Nathan and Gorman (1998) used findings from replicated randomised controlled trials to show that 38 specific treatments were more efficacious than placebo in 14 psychiatric disorders. However, not all have been demonstrated to be effective, and very few have been trialled with individuals with comorbid disorders.

Table 1: Ten leading causes of burden of disease and injury in 15–24 year olds in Australia in rank order

Table 1 is presented as two lists in this HTML version for accessibility reasons. It is presented as a table in the PDF version.

  1. Road traffic accidents
  2. Alcohol dependence
  3. Suicide
  4. Bipolar affective
  5. Heroin dependence
  6. Schizophrenia
  7. Depression
  8. Social phobia
  9. Borderline personality
  10. Generalised anxiety disorder
Females:Top of page
  1. Depression
  2. Bipolar affective
  3. Alcohol dependence
  4. Eating disorders
  5. Social phobia
  6. Heroin
  7. Asthma
  8. Road traffic accidents
  9. Schizophrenia
  10. Generalised anxiety disorder