Discussion
Main Findings
Our study, based on a nationally representative sample of the US adult population, shows that among individuals who have an illegal drug use disorder, comorbid mood and anxiety disorders are not associated with treatment for illegal drug use disorders. However, common psychiatric comorbidities predict an over twofold increase in perceived unmet need for treatment, which is not accounted for by socio-demographic characteristics, treatment for mood and anxiety disorders and comorbid alcohol use disorder. Overall, these findings suggest that individuals who concomitantly have an illegal drug use disorder and mood or anxiety disorders require special attention from mental health and addiction specialists; integrated mental health and substance use programs could prove effective in addressing their treatment needs.
Treatment for Illegal Drug Use Disorders
Our result of no association between comorbid mood and anxiety disorders and treatment for illegal drug use disorders contrasts with findings of studies which simultaneously examined illegal drug use and alcohol-related disorders.[21] However, in line with prior research, we found that treatment for illegal drug use disorders was associated with the number of drugs used,[21] suggesting that the severity of substance use problems is a relevant predictor of treatment seeking.
Perceived Unmet Need for Treatment
Mood and anxiety disorders were associated with high levels of unmet need for illegal drug use disorder treatment. Overall, the magnitude of the association was similar whether the comorbid disorder was a mood or an anxiety disorder, suggesting that it is the presence of comorbidity rather than its type that is especially relevant. After controlling for treatment for mood and anxiety disorders as well as comorbid alcohol use disorder, only anxiety disorders were associated with an approximately two-fold increase in the likelihood of perceived unmet need for treatment. One possible explanation of this finding is that individuals who simultaneously have illegal drug use problems and mood disorders seek treatment for their mood disorder, because of lesser stigma, easier access, and simpler reimbursement schemes.[21] This does not appear to be the case of participants with comorbid anxiety disorders, who are less likely to seek mental health treatment.
Elevated rates of perceived unmet need for treatment for illegal drug use related disorders may be due to the scarcity of specialized services, absence of adequate programs for simultaneous treatment of co-occurring illegal drug use and psychiatric disorders, as well as stigma. Moreover, perceptions of the severity of the drug use problem and of treatment effectiveness may also play a role. Currently available treatment services for people who have illegal drug use problems other than crack/heroin may not be sufficient, leading to low access and high perceived unmet need for treatment. Furthermore, when illegal drug use disorders are not addressed by mental health services not specialized in addiction, individuals may have the impression that their drug use problems are not serious enough to require treatment or that adequate treatment is not available.
Limitations and Strengths
We need to acknowledge several study limitations. First, illegal drug use and psychiatric disorders, as well as treatment for illegal drug use disorder and perceived unmet need for treatment were studied over participants' lifetime and we are not able to assess trajectories of substance use and treatment. Research shows that the association between addictive behaviors and mood and anxiety disorders is bidirectional, but common psychiatric disorders most frequently precede onset of substance dependence.[28] Thus, in our study mood and anxiety disorders probably preceded treatment for illegal drug use disorders. Second, data on illegal drug use were collected by federal employees and could be underreported. Nonetheless, the NESARC study interviews were confidential and the reliability of the AUDADIS-IV is good to excellent, therefore the influence of information bias on our measures should be limited.[29–31] Prior to fieldwork, Census employees received extensive training in the AUDADIS, which was created to be administered by non-clinicians, similar to several standardized epidemiological interviews.[30] Moreover, the reliability of the AUDADIS have previously been verified and described.[31] Third, access to treatment for illegal drug use disorders and unmet need for treatment were ascertained using a single measure specific to the NESARC study, previously used by other researchers.[32] Fourth, the study population did not include individuals who are institutionalized, who may have elevated rates of both illegal drug use disorders and unmet treatment needs. Therefore, the association between mood and anxiety disorders and unmet need for illegal drug use treatment may be stronger than we report. Fifth, we were not able to examine whether access to treatment for illegal drug use disorders varied between rural and urban areas, by state, or type of treatment unit.
Our study also has strengths. First, we studied a nationally representative sample of the US adult population which limits the possibility of selection bias. Second, psychiatric disorders were assessed using a structured diagnostic questionnaire, which evaluates the presence of clinically relevant disorders as measured by DSM-IV criteria.[26] Third, we investigated factors associated with service use, but also unmet perceived need for treatment for illegal drug related disorders.
Integrated Treatment of Comorbid Illegal Drug Disorders and Mental Health Problems
National surveys indicate that only half of US mental health centers offer treatment programs for individuals with 'dual diagnosis' and this proportion did not significantly change during the past decade.[6] Lack of progress in this area can be explained by a) insufficient clinical knowledge, b) the absence of standardized screening procedures to identify individuals who have an illegal drug use disorder,[33,34] and c) incomplete treatment guidelines in case of dual diagnosis and insufficient organizational support.[35] Patients themselves repeatedly report that illegal drug use disorders are often ignored and not treated by mental health care providers.
According to a proposed four-quadrant continuity-of-care model, a) persons with low severity psychiatric and substance use disorders should be treated in the primary health care system (quadrant I); b) persons with high severity psychiatric disorders and low severity substance use disorders should be treated in the mental health system (quadrant I); c) persons with low severity psychiatric disorders and high severity substance use disorders should be treated in the addiction treatment system (quadrant III); d) persons with high severity psychiatric and substance use disorders need to use multiple treatment systems and make more frequent use of emergency and inpatient services (quadrant IV).[36] This relies on a well-functioning referral and collaboration system between the point-of-contact (primary care, emergency departments, etc.) and specialized care. Number of studies conducted in the last 15 years provided evidence for the effectiveness of integrated treatment for comorbid psychiatric and substance use disorders.[37–39] Nevertheless the integration of mental health and substance use treatment services has produced uneven results due to a number of barriers such as the absence of regulations, the lack of appropriate financial resources,[40] the lack of sufficiently experienced staff,[41] high rates of stuff turn over,[42] and the lack of tools and implementation strategies.[43] In a context of low availability of integrated treatment, progress has been made with the development and continued validation of external rating tools (DDCAT -the Dual Diagnosis Capability in Addiction Treatment and DDCMHT-the Dual Diagnosis Capability in Mental Health Treatment) to determine the capability of substance abuse and mental health service providers to treat co-occurring disorders.[44,45] Previous evaluations using the DDCAT showed that the majority of substance abuse programs were rated less than 'capable' and only few programs achieved or exceeded the 'capable' level.[46,47] Overall, growing evidence stresses the importance of routine screening for illegal drug use disorders in patients with other psychiatric disorders and the integration of addiction services into psychiatric and medical treatment settings to promote symptom reduction and stable remission.
BMC Psychiatry. 2014;14(89) © 2014 BioMed Central, Ltd.
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