Co-Occurring Mental Health and Substance Use Disorders

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It is well-understood that substance use disorders (SUDs) carry significant physiological, psychological and social risk factors. These risks are increased and further complicated in cases where patients also experience concurrent mental health disorders. For patients who experience co-occurring substance use and mental health disorders (a condition often referred to as dual diagnosis or comorbidity), there are a number of critical aspects that should be considered in developing an integrated treatment plan that addresses both types of disorders, in addition to the considerable interactions posed by their comorbidity.

Prevalence and Common Characteristics of Co-Occurring Disorders

Research has established that patients who are diagnosed with co-occurring mental health and SUDs experience several elevated risk factors as compared to patients with singular diagnoses of either a mental health disorder or a SUD. Specifically, dual diagnosis patients demonstrate more persistent and severe symptoms of their disorders; tend to be more treatment-resistant; have higher risk of suicide; are more frequently targeted as victims of crime; and report significantly higher rates of social, financial and legal concerns.^{1, 2, 3, 4} These outcomes are amplified in dual diagnosis patients because symptoms and risk factors of both types of disorders often tend to be synergistic rather than additive (i.e., the combined symptomology is more severe than the sum of both disorders’ symptoms).^{1, 4} Further, patients with dual diagnosis are often not ideal candidates for various psychopharmacological treatments because of an increased risk of abuse potential.^{4, 8} As the struggles related to dual diagnosis have come to light over the past several years, it is unsurprising that there has been a subsequent increase in the number of studies attempting to better understand the onset and interaction of comorbid substance use and mental health disorders.

A 1996 national survey of comorbidity found that individuals diagnosed with any mental disorder in their lifetime were 2.4 times more likely to also have an alcohol or drug use disorder during their lifetime. These findings were replicated with additional surveys in 2001 and 2003,^{6, 7} where rates of comorbidity were found to be highest for bipolar disorders (the lifetime prevalence rate among individuals with any bipolar disorder for any SUD was 47.3 percent; lifetime prevalence for any SUD jumps to 60.3 percent among individuals diagnosed with bipolar I disorder).⁸ Comorbidity rates were also high for major depression and alcohol use disorders (the lifetime prevalence rate for any alcohol use disorder among individuals with major depression was 40.3 percent).^{8, 9} Increased risk for the development of a SUD has also been documented for anxiety disorders, particularly panic disorder and post-traumatic stress disorder (PTSD), and antisocial personality disorder (ASPD) (although distinguishing between primary and secondary diagnoses for SUDs and ASPD is especially difficult since there can be a great deal of overlap in the diagnostic criteria for these disorders).⁴ It is estimated that approximately 37 percent of all individuals with alcohol dependence also suffer from one or more other concurrent mental health disorders.²

Causation Versus Correlation

Do mental health disorders cause the development of problematic substance use, or do SUDs cause the development of mental health symptoms? Clinical providers often struggle with determining the etiology (or cause) of dual diagnosis conditions, as this can be difficult to assess and has a significant impact on how to proceed with treating each condition.^{1, 8} For example, if a pre-existing SUD is causing mood disorder symptoms, such as depression or anxiety, then some common treatments for these mood symptoms (particularly pharmacological treatments) may not be the most effective or suitable course of action; however, if mental health symptoms exist in the absence of substance use, it may be possible that these mental health treatments may also be valuable for successful treatment of the SUD.⁸ Both practitioners and researchers also have a significant interest in determining whether one type of disorder poses a threat of developing the other, as this has critical implications for prevention and early intervention efforts.^{1, 4}

Determining any level of causation between comorbid mental health and SUDs can be quite challenging, as both types of disorders occur as the primary diagnosis among dual diagnosis populations in fairly even numbers, and diagnostic criteria can sometimes overlap. According to the 1996 U.S. National Comorbidity Survey, it was determined that 51.4 percent of respondents who were diagnosed with a SUD in their lifetime also met the criteria for one or more mental health disorders; conversely, 50.9 percent of individuals who had been diagnosed with a mental health disorder in their lifetime also had a history of substance abuse or dependence.⁵ Studies have found evidence to support that a significant portion of dual diagnosis patients develop SUDs in response to self-medication of existing mental health symptoms;¹⁰ yet conversely, the inclusion of alcohol- and drug-induced disorders in the DSM illustrates the prevalence of mental health disorders that develop as a result of SUDs.² In the case of overlapping symptoms, clinical practice generally prescribes that mental health symptoms persisting in the absence of substance use are the result of a primary mental health condition,⁸ and large-scale analyses of retrospective data consistently find that mental health symptoms tend to present at an earlier age than symptoms of SUDs,^{1, 11} which both suggest that mental health disorders develop first; however, studies with dual diagnosis patients often uncover trends that suggest a third possibility—that both disorders may develop as a result of one or more external factors.^{1, 2, 8}

Understanding all of the variables that can influence the development of dual diagnosis requires awareness of how these elements often interact in highly complex ways. As noted previously in this paper, even just considering clinical factors, there are many varying levels of risk for a comorbid SUD based on the type of primary mental health disorder an individual is diagnosed with.^{1, 2, 4, 8} Outside of these clinical factors, environmental and behavioral factors may also play significant roles in the development, presentation and diagnosis of both types of disorders. For this reason, it is a common belief of clinicians and researchers that dual diagnosis is not necessarily a case of one condition simply causing the other, but rather a case of two correlating conditions that are markers of external stressors or variables.¹ It is widely accepted that the development of both mental health disorders and SUDs can be impacted by stress or trauma presented by any number of social, economic, medical or legal factors. A 2017 study of sociological variables found that, in the United States, there may be also be a cultural effect for the development of dual diagnosis; when controlling for age, gender, marital status, number of children in the household, region of residence, community type, smoking behaviors and religiosity, comorbid SUD and psychiatric disorders were significantly more prevalent among U.S.-born natives and European-born immigrants than individuals who immigrated from other locations,⁹ and previous research has found that, for families of Latino origin, the likelihood for developing an SUD increases in each subsequent generation after immigration to the United States.¹² Biological studies have also uncovered evidence for a genetic predisposition for the development of dual diagnosis, particularly for individuals with genetic markers that correlate with increased risk for externalizing mental health disorders.¹ All of these external risk factors commonly overlap, which generally makes the study of any single variable’s effect on the risk for comorbidity impossible.

Conclusion

Understanding the relationship of co-occurring mental health and substance use disorders goes far beyond treating both disorders separately. Dual diagnosis presents challenges in the form of complex symptom presentation, increased treatment resistance and the often-contradictory treatment practices for each type of disorder. Learning how dual diagnosis first develops, exploring potential interventions to prevent secondary disorders when an individual is at risk for dual diagnosis, and establishing a combined treatment protocol to consider the synergistic combination of both types of disorders (as well as any external factors that have contributed to the development and exacerbation of symptoms for both disorders) are critical for the successful treatment of comorbid mental health and substance use disorders in the future.