Introduction
Substance use disorders (SUDs) and other mental health disorders commonly co-occur and are often referred to as ‘dual diagnosis’ or ‘comorbidity’ (EMCDDA Reference Torrens, Mestre-Pintó and Domingo-Salvany2015). According to the Global Burden of Disease study, mental and substance use disorders are significantly correlated and contributed to more than one million years lived with disability in Europe in 2019 (Castelpietra et al. Reference Castelpietra, Knudsen, Agardh, Armocida, Beghi and Iburg2022). For example, recent data from the National Epidemiological Survey on Alcohol and Related Conditions conducted in the US indicated that 25.8% of all patients with any past-year psychiatric disorder had a dual diagnosis (Jegede et al. Reference Jegede, Rhee, Stefanovics, Zhou and Rosenheck2022). Studies from Spain report lifetime prevalence rates of comorbid mental health disorders in patients in treatment for SUD ranging from 62 to 67%, depending on the treatment setting, and in a multi-country study in patients diagnosed with schizophrenia, 19 to 35% was found to have a lifetime comorbidity of a SUD (Nocon et al. Reference Nocon, Bergé, Astals, Martín-Santos and Torrens2007; Carrà et al. Reference Carrà, Johnson, Bebbington, Angermeyer, Heider, Brugha, Azorin and Toumi2012; Vergara-Moragues et al. Reference Vergara-Moragues, González-Saiz, Lozano, Betanzos Espinosa, Fernández Calderón, Bilbao-Acebos, Pérez García and Verdejo García2012; Araos et al. Reference Araos, Vergara-Moragues, Pedraz, Pavón, Campos Cloute, Calado, Ruiz, García-Marchena, Gornemann, Torrens and Rodríguez de Fonseca2014; EMCDDA Reference Torrens, Mestre-Pintó and Domingo-Salvany2015). A complex interplay exists between mental illness, substance use, homelessness, and physical health problems, with these factors interacting and potentially exacerbating one another (Coid et al. Reference Coid, Zhang, Bebbington, Ullrich, de Stavola, Bhui and Tsai2021; Barry et al. Reference Barry, Anderson, Tran, Bahji, Dimitropoulos, Ghosh, Kirkham, Messier, Patten, Rittenbach and Seitz2024). Patients with a dual diagnosis show a higher risk of suicide, more social disadvantages and lower quality of life (Szerman et al. Reference Szerman, Lopez-Castroman, Arias, Morant, Babín, Mesías, Basurte, Vega and Baca-García2012, Jegede et al. Reference Jegede, Rhee, Stefanovics, Zhou and Rosenheck2022). They are also frequently excluded from clinical studies, restricting the advancement of evidence-based treatment for these patients (Dennis et al. Reference Dennis, Roshanov, Naji, Bawor, Paul, Plater, Pare, Worster, Varenbut, Daiter, Marsh, Desai, Samaan and Thabane2015; Zimmerman et al. Reference Zimmerman, Clark, Multach, Walsh, Rosenstein and Gazarian2016). Considering the high prevalence and negative consequences of comorbid substance use and mental health disorders, for the individual and society, adequate treatment of these disorders should be considered a public health priority (Whiteford et al. Reference Whiteford, Degenhardt, Rehm, Baxter, Ferrari, Erskine, Charlson, Norman, Flaxman, Johns, Burstein, Murray and Vos2013). This need has also been recognised by international organisations and authorities, such as the council of the European Union (EU), the European Union Drugs Agency (EUDA), the World Health Organization (WHO), and the United Nations Office on Drugs and Crime (UNODC) (EMCDDA Reference Torrens, Mestre-Pintó and Domingo-Salvany2015; Volkow et al. Reference Volkow, Torrens, Poznyak, Sáenz, Busse, Kashino, Krupchanka, Kestel, Campello and Gerra2020; General Secretariat of the Council of the European Union 2023).
Guidelines and standards are widely used tools that translate evidence-based recommendations into practice, promoting effective interventions and harmonisation (Ferri and Griffiths Reference Ferri, Griffiths, el-Guebaly, Carrà and Galanter2015). Clinical guidelines provide a guide to recommended practice, while quality standards are principles and sets of rules that are typically set by recognised (inter)national bodies and can serve as a statement of expected requirements for the implementation of evidence-based interventions (Ferri and Griffiths Reference Ferri, Griffiths, el-Guebaly, Carrà and Galanter2015; EMCDDA 2021). Guidelines and standards may operate alongside each other, with guidelines providing a benchmark against which to evaluate the quality of services being delivered, and standards being used to implement interventions (EMCDDA 2021). Both international guidelines and quality standards in healthcare aim to improve the quality of patient care and facilitate global collaboration by bridging the gap between best evidence and clinical practice (Grol et al. Reference Grol, Cluzeau and Burgers2003; De Leo et al. Reference De Leo, Bloxsome and Bayes2023). Two recent systematic reviews assessed the quality of clinical guidelines for dual diagnosis and found that there is a scarcity of comprehensive guidelines, noting that they generally rely on combinations of treatments for individual disorders (Hakobyan et al. Reference Hakobyan, Vazirian, Lee-Cheong, Krausz, Honer and Schutz2020; Alsuhaibani et al. Reference Alsuhaibani, Smith, Lowrie, Aljhani and Paudyal2021). Moreover, the guidelines provide little recommendation for evaluating different models of treatment integration. These reviews show that, despite some limitations, several clinical guidelines developed worldwide are available to support clinical practice. Quality standards for the treatment of comorbid substance use and mental health disorders, however, are lacking. This article aims to explore the need for and availability of quality standards in the field of comorbid substance use and mental health disorders.
The need for quality standards in the treatment of comorbid substance use and mental health disorders
Having quality standards, that are operationalised into reliable, valid, and feasible quality measures, can help improve evidence-based care and reveal gaps and areas of poor performance (Hermann and Palmer Reference Hermann and Palmer2002). Moreover, they can support the implementation and delivery of evidence-based interventions, a crucial step for the success of any intervention (Ferri et al. Reference Ferri, Dias, Bo, Ballotta, Simon and Carrá2018). Having a multitude of heterogeneous standards, on the other hand, can lead to increased burden of data collection and reduced usefulness of results (Harris et al. Reference Harris, Gupta, Bowe, Ellerbe, Phelps, Rubinsky, Finney, Asch, Humphreys and Trafton2015). In this regard, international quality standards, developed by relevant experts and authorities and adaptable to the local context, can be helpful in improving the quality of interventions and ensuring efficient use of limited resources.
In the field of drug demand reduction, several international organisations have developed quality standards, and quality assurance is recognised as a priority in many European countries and in the EU drug strategies (EMCDDA 2021). For example, in 2015, the Council of the European Union concluded over a set of 16 ´minimum quality standards for drug demand reduction´ inspired, among others, by the European financed project EQUS (Uchtenhagen and Schaub Reference Uchtenhagen and Schaub2011; General Secretariat of the Council of the European Union 2015), and in 2021, a collaboration of international organisations published the ´key quality standards for service appraisal for treatment of drug use disorders´, based, among others, on the UNODC/WHO ´International Standards for the Treatment of Drug Use Disorders´ (UNODC/WHO 2020; Dale-Perera Reference Dale-Perera2021). Although this last report includes the treatment of comorbid psychiatric and physical disorders as an essential part of treatment for drug use disorders, none of these drug demand reduction quality standards provide specific standards for the treatment of comorbid substance use and mental health disorders.
Yet, in the field of dual diagnosis, supporting the process of harmonisation and implementation of evidence-based interventions through the adoption of quality standards is especially relevant. The organisation of care for people with dual diagnoses in Europe varies widely between member states, with most countries maintaining separated mental health and SUD treatment networks (Carrà et al. Reference Carrà, Bartoli, Brambilla, Crocamo and Clerici2015; EMCDDA Reference Torrens, Mestre-Pintó and Domingo-Salvany2015). The lack of consensus on optimal treatment setting and therapeutic approach contributes to considerable variability in clinical practice, and studies have shown that patients with dual diagnosis are less likely to receive effective treatment (Watkins et al. Reference Watkins, Burnam, Kung and Paddock2001; EMCDDA Reference Torrens, Mestre-Pintó and Domingo-Salvany2015; San et al. Reference San, Arranz, Arrojo, Becoña and Bernardo2016; Coughlin et al. Reference Coughlin, Pfeiffer, Ganoczy and Lin2021). In addition to the available clinical guidelines, quality standards are needed to promote a common understanding of quality care for comorbid substance use and mental health disorders.
Existing quality standards for treatment of comorbid substance use and mental health disorders
In 1998, Minkoff proposed national standards for best practices for treatment of patients with dual diagnoses in the United States, focusing on the system level (Minkoff Reference Minkoff2001). These standards outline a set of principles aimed at guiding system design. One of these guiding principles is that “comorbidity should be expected, not considered an exception”, meaning that the entire system of care should be designed to be accessible to patients with dual diagnoses (Minkoff Reference Minkoff2001). Additionally, it is stated that both substance use and mental health disorders should be treated as primary disorders, requiring specific and appropriate care by expert professionals. Other principles include the adoption of a recovery and continuum of care model, inclusive and appropriate admission criteria, and an assertive care approach (Minkoff Reference Minkoff2001). Some of these principles were also included in reports published many years later by the New South Wales Ministry of Health and Queensland Health in Australia (New South Wales Ministry of Health 2015; Queensland Health 2021). Notably, mirroring the standards proposed by Minkoff (Reference Minkoff2001), the first of the Queensland Health ´principles of care for co-occurring SUDs and other mental health disorders´ is “individuals with co-occurring SUDs and other mental health disorders are the expectation, not the exception” (Queensland Health 2021). Person-centred, holistic, and trauma-informed care, effective collaboration between health and other services, and the shared role of staff are other principles included in this report (Queensland Health 2021). Both the Queensland Health and the New South Wales Ministry of Health documents highlight the principle of the ´no wrong door´ approach, stating that all services should respond to an individual´s needs, providing appropriate services accessible through multiple points of entry (New South Wales Ministry of Health 2015; Queensland Health 2021). Referrals between services should only be made when needed and with a conscientious handover (Queensland Health 2021). In addition, the New South Wales Ministry of Health ´effective models of care for comorbid mental illness and illicit substance use´ report includes recommendations on screening, assertive and coordinated care, workforce development, and regular evaluation of services (New South Wales Ministry of Health 2015). Some other countries, such as New Zealand and Ireland, also have national documents highlighting good practices and providing guidance on the commission and provision of effective treatment, but without specifying quality standards or principles (Department of Health 2002; Ministry of health 2010; Public Health England 2017; National Working Group for Dual Diagnosis 2023).
While the above mentioned documents outline general, aspirational standards and principles, the National Institute for Health and Care Excellence (NICE) in the UK in 2019 published the ´quality standards on coexisting severe mental illness and substance misuse´, consisting of a set of four specific, concise, and measurable quality statements: “people […] with suspected or confirmed severe mental illness are asked about their use of alcohol and drugs”, “people […] are not excluded from mental health services because of coexisting substance misuse or from substance misuse services because of coexisting severe mental illness”, “people […] with coexisting severe mental illness and substance misuse have a care coordinator working in mental health services when they are identified as needing treatment from secondary care mental health services” and “people […] with coexisting severe mental illness and substance misuse are followed up if they miss any appointment” (National Institute for Health and Care Excellence (NICE) 2019). Each statement is accompanied by specific quality measures, categorised into three levels: structure, process and outcome level, applying the three-level framework suggested by Donabedian (Reference Donabedian2005). Additionally, potential data sources are provided to assess each measure (National Institute for Health and Care Excellence (NICE) 2019).
In a quick review of the 2024 EUDA workbooks, which provide qualitative information on a range of drug-related topics and are submitted to the EUDA annually by each EU member state plus Norway and Turkey, no additional specific quality standards for dual diagnosis were identified. However, the workbooks only include questions about quality assurance in drug treatment services and an optional question about comorbidity, with no specific question on quality assurance in treatment of comorbidity, thus it is possible that other standards are available in the countries but were not reported in the workbooks. The EUDA is currently preparing the launch of EU-QUALITY, a project focused on developing and supporting the implementation of quality management systems in drug demand reduction services in Europe, which will also provide a comprehensive overview of quality standards.
As the aim of this article was not to perform an in-depth review of all available quality standards, it is possible that there are other national standards available that have not been identified or reported here.
Discussion
Quality standards and quality assurance have gained importance in all healthcare areas, including substance use disorder treatment, over the past decades. They facilitate the implementation of evidence-based interventions, support harmonisation of care, and help guide appropriate allocation of limited resources. Although comorbid substance use and mental health disorders are highly prevalent and are associated with various adverse outcomes, the field of dual diagnosis appears to be lagging behind when it comes to quality standards. This might in part be due to the historical separation between mental health and SUD care networks, leading to unclarity not only on who is clinically responsible for the care of patients with comorbid substance use and mental health disorders, but possibly also to hesitancy from international organisations on both sides to take on this subject. Yet, as has been mentioned in some of the existing national standards and as evidenced by epidemiological studies, comorbidity should be expected, not considered an exception. Therefore, it is imperative to ensure adequate attention to dual diagnoses on the international stage. The EUDA has published a comprehensive overview of the situation in Europe and is in the process of establishing routine monitoring of data on comorbidity within the framework of the Treatment Demand Indicator (EMCDDA 2012, Reference Torrens, Mestre-Pintó and Domingo-Salvany2015), and UNODC, for the Commission on Narcotic Drugs in 2022, published a discussion paper on comorbidities in drug use disorders (UNODC 2022). These efforts show a willingness and commitment from these organisations to improve the care for people with comorbid substance use and mental health disorders, and the development of international quality standards could be the logical and necessary next step in this endeavour.
Financial support
This research received no specific grant from any funding agency, commercial, or not-for-profit sectors.
Competing interests
The authors declare none.
Ethical standards
The authors assert that all procedures contributing to this work comply with the ethical standards of the relevant national and institutional committee on human experimentation and with the Helsinki Declaration of 1975, as revised in 2008.
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