Dual disorders: health and social responses

Introduction

This page provides an overview of the main considerations when planning and delivering health and social responses for people experiencing co‑occurring mental health and substance use disorders. It examines the availability and effectiveness of these responses and explores the implications for policy and practice.

Last update: 21 May 2026

What are dual disorders?

Dual disorders (also referred to as comorbidity, concurrent disorders, co-occurring disorders or dual diagnosis) consist of the co-occurrence of a substance use disorder and one or more mental health disorders in the same individual.

How do mental health disorders and substance use disorders interact?

The relationship between mental health and substance use is complex and not always clear. The two disorders share overlapping risk factors and often occur together. However, the pathways vary depending on the type of mental health disorder, the substances used, the patterns of use, and other social and environmental factors.

Dual disorders can occur concurrently, meaning both arise simultaneously; sequentially, where one emerges after the other; or independently, with no causal link between them, still occurring at the same time.

In some instances, one disorder may increase the likelihood of developing or exacerbating the other. Mental health problems can lead to substance use disorders, and substance use can trigger mental health problems. For example, people experiencing depression may use drugs to cope with their emotional pain. Similarly, individuals who have lived through traumatic events may turn to substance use in an attempt to reduce distressing memories or feelings. Over time, regular drug use can also affect how the brain works, increasing the chances of developing mental health problems or worsening existing ones (including conditions such as depression, anxiety and psychosis) (Sweileh, 2024).

Individuals with dual disorders often experience more intense difficulties, respond less well to treatment, relapse more frequently and are more likely to require hospital care than those with only one disorder.

This complexity poses significant challenges for both assessment and intervention and creates serious difficulties for those affected and the services that support them.

Current concerns

The presence of mental health disorders in individuals with substance use disorders has become an increasing focus of concern in Europe. This trend intensified during the COVID-19 pandemic, as increased social isolation, heightened stress and disruptions to healthcare services contributed to worsening mental health and increased substance use for many individuals (Santomauro et al., 2021).

The co-occurrence of these disorders poses a major challenge due to the complexity of their management and association with poor outcomes for affected individuals.

Mental health disorders are associated with more complex clinical profiles among individuals with substance use disorders, influencing psychosocial functioning, quality of life and service engagement. Conversely, among individuals with mental health disorders, the co-occurrence of substance use is linked to less stable illness trajectories, including an increased likelihood of symptom recurrence, more frequent contact with acute care services and an elevated mortality risk (UNODC, 2022).

People with dual disorders show a higher prevalence of suicidal ideation and suicide, are more likely to engage in high-risk behaviours often associated with infections such as human immunodeficiency virus (HIV), hepatitis B virus (HBV) and hepatitis C virus (HCV), and face higher rates of unemployment, homelessness and contact with the criminal justice system (HSE, 2023; Volkow and Blanco, 2023).

Because mental and substance use disorders impact each other in a continuous cycle, identifying and addressing both problems together can be challenging, especially as their symptoms may look similar and because drug use can interfere with mental health treatments (Sweileh, 2024).

Prevalence

Dual disorders are common among people with substance use problems and are a key concern for policy and treatment planning in Europe.

Studies in European treatment settings estimate that between 42 % and 90 % of people with substance use disorders also have or have had a co-occurring mental health disorder, with figures varying by treatment setting and population (EMCDDA 2015; UNODC 2022). Conversely, it is estimated that 30 to 50 % of people with severe mental illnesses who attend mental health services also have substance use disorders (HSE 2023). Overall, there are significant gaps in the current prevalence research in this field. As these estimates are drawn from earlier studies, they should be treated with caution.

In addition, the available data on the prevalence of mental health disorders among people who use drugs are heterogeneous. Reported prevalence rates may vary according to factors such as the psychoactive substances used, the population studied (general, clinical or special populations), the gender balance, the study settings (primary healthcare, mental health or drug use treatment services, outpatient or inpatient facilities), the definition for diagnosis of dual disorders used, and the drug epidemiology patterns in different European countries.

Research also indicates that certain populations are disproportionately affected by dual disorders, including young people, people who experience homelessness and individuals in custodial settings (EMCDDA, 2023a; Taggart et al., 2025). In addition, women exhibit distinct patterns of dual disorders that may reflect gender-specific vulnerabilities and treatment needs (EMCDDA, 2023b).

Better data are needed on the prevalence of dual disorders among people who use drugs, and on drug use and the non-medical use of medicines among people with mental health conditions, in order to better understand what the situation in Europe is and improve the availability and adequacy of treatment responses.

Some initiatives are already underway in Europe to strengthen data availability and comparability. Notably, in 2024, a standardised measure of mental health disorders was introduced into the data collected from people entering drug treatment as part of the reporting by European countries to the European Union Drugs Agency (EUDA).

Frequent co-occurring conditions

Mood disorders

Epidemiological and clinical evidence shows that substance use disorders frequently co-present with mood disorders, particularly major depression and bipolar disorder, where substance use can both worsen emotions and instability and develop as an unhealthy way of coping (González-Pinto et al., 2022; Torrens et al., 2022).

Anxiety and stress disorders

Anxiety disorders or post-traumatic stress disorder are strongly associated with substance use, often influenced by past trauma and increased sensitivity to stress (Sáiz et al., 2022).

Schizophrenia or other primary psychotic disorders

High rates of dual disorders are consistently observed between substance use disorders and schizophrenia or other primary psychotic disorders, reflecting shared neurobiological vulnerabilities and having significant implications for recovery and daily functioning (Arranz et al., 2022; Murrie et al., 2020).

Personality disorders

Personality disorders, especially those characterised by emotional dysregulation and impulsivity, show particularly strong associations with problematic substance use (Stetsiv et al., 2023).

Neurodevelopment disorders

Neurodevelopment disorders, particularly attention-deficit/hyperactivity disorder, are increasingly recognised as an early factor that may contribute to the later development of dual disorders (Cunill et al., 2022).

Substances commonly associated with dual disorders

The substances most commonly associated with dual disorders include alcohol, opioids, cocaine, cannabis, and sedatives or hypnotics.

Opioids

Opioids are linked to both dependence and changes in the emotional state, most commonly depression (Ghabrash et al., 2020).

Stimulants

Stimulants such as cocaine and amphetamines are associated with the onset or exacerbation of psychotic symptoms (Moran et al., 2024; Murrie et al., 2020).

Cannabis

Chronic use may affect mood regulation, contribute to depressive symptoms and trigger psychotic episodes (European Union Drugs Agency, 2025).

Sedatives or hypnotics

Long-term use of sedatives or hypnotics may aggravate anxiety disorders.

Across these diagnostic profiles, dual disorders are associated with greater clinical severity, increased social marginalisation and poorer treatment outcomes, underscoring the need for integrated diagnostic and therapeutic approaches (Plana-Ripoll et al., 2019).

Health and social responses to dual disorders

Access to healthcare

Dual disorders among people who use drugs are frequently under-recognised in clinical practice, reflecting the challenges of diagnosis and the frequent separation of mental health and substance use care systems.

The most common barriers that individuals with dual disorders face when trying to access appropriate treatment services are associated with the separation of mental health and drug use treatment response networks, and the insufficient expertise of healthcare professionals to effectively address both types of disorders (Sweileh, 2024). These individuals often experience difficulties in identifying, accessing and navigating the necessary mental health and substance use services and may not receive the integrated, coordinated and comprehensive care that they need to address both disorders simultaneously. For example, individuals are often immediately referred to another service at their first point of contact because of a co-occurring disorder, which can delay care and increase the risk of disengagement. Integrated treatment models following the ‘no wrong door’ approach seek to address this, ensuring coordinated, comprehensive care for both mental health and substance use disorders at their first point of contact.

Detection

Available evidence supports the systematic identification of dual disorders and the delivery of integrated interventions that simultaneously address both disorders within coordinated interdisciplinary models of care (UNODC, 2022). However, the identification of mental disorders among people who use drugs presents diagnostic challenges, as substance use can affect cognition, emotions and behaviour in ways that intersect with the core psychiatric diagnostic criteria.

This overlap makes it difficult to determine whether the observed symptoms reflect the effects of substance use or the presence of an independent mental health disorder, particularly given that clinical presentations can change over time and are influenced by context.

As a result, dual diagnosis should not be understood simply as the co-presence of two distinct conditions, but rather as a dynamic diagnosis shaped by substance-use-related effects, underlying vulnerabilities and evolving illness trajectories that together pose challenges for classification and assessment (Carrà et al., 2015; Plana-Ripoll et al., 2019).

Implementing a screening routine to detect dual disorders is important, as these cases may be missed when patients seek care from services specialised in substance use disorders with limited access to mental health expertise, when substance use disorders are managed in primary care or when patients present to health services for other, unrelated reasons (EMCDDA, 2015).

There are several tools to detect mental health disorders in individuals with substance use disorders, such as standardised clinical interviews and screening instruments (interviews, scales) (EMCDDA, 2015; HSE, 2023). Different tools may be used according to the setting in which they are applied, the time available to conduct the assessment, and the experience and professional background of the staff applying them.

If mental health disorders are detected, a definitive diagnosis and access to adequate treatment must be organised.

Treatment

The importance of adopting a therapeutic approach that considers both disorders is widely recognised. However, there is still a lack of consensus regarding the most appropriate treatment setting and pharmacological and psychosocial strategies. In practice, treatment of dual disorders typically includes pharmacotherapy, relapse prevention and psychosocial interventions, alone or in combination.

Pharmacological management

The pharmacological management of dual disorders is complex. In addition to the efficacy of the pharmacotherapy, tolerability and safety must be assessed. Special consideration must be given to:

• the propensity of the substance prescribed to be used in non-medical situations;
• possible pharmacological interactions with the use of illicit substances;
• possible pharmacological interactions with other ongoing substance use treatments, such as opioid agonist treatment, or treatments for concurrent diseases such as HIV, HCV or tuberculosis.

Psychosocial interventions

Psychosocial therapies for dual disorders include motivational interviewing, cognitive behavioural therapy, contingency management, family-based interventions, and internet and digital-based interventions (Dugdale et al., 2019; HSE, 2023).

Trauma-informed care

Trauma-informed care plays an important role in the treatment of dual disorders. This is particularly relevant for women, who are more likely to have experienced trauma during the course of their life, including gender-based and interpersonal violence. This approach has several aims: to recognise the signs and symptoms of trauma in patients (and staff of mental health and substance use services) and the role this can play in their lives; to avoid the repetition of trauma; and to restore feelings of safety and self-worth (EMCDDA, 2023b; HSE, 2023).

Evidence and best practices

There are relatively few studies on the efficacy of treatments in this area, making it difficult to develop evidence-based recommendations for their treatment. In recent years, a wide range of pharmacological and psychosocial treatment strategies for the most common comorbidity dyads have been examined (Arranz et al., 2022; Cunill et al., 2022; González-Pinto et al., 2022; Sáiz et al., 2022; Torrens et al., 2022; Volkow and Blanco, 2023). While some promising strategies have been identified, further studies are needed to improve the evidence base for dual disorders treatments and enable the development of evidence-based guidelines (HSE, 2023; Hunt et al., 2019; Subodh et al., 2018).

Nevertheless, and despite the limited evidence, these studies indicate that best practices may involve integrated mental health and substance use treatments, emphasising inclusion in treatment, ongoing evaluation of substance use patterns, and coordinated care aimed at matching treatment to the severity of both disorders and the stages of change (HSE, 2023; UNODC, 2022). Optimal management also requires a good understanding of the efficacy, interactions and side effects of pharmacological and psychological treatments (Hunt et al., 2019).

Models of care

A model of care can be defined as the manner in which health services are delivered. It refers to how specific individuals and populations access healthcare, which team provides it, and when and where it is provided.

There are currently three main models of care to address dual disorders:

• sequential treatment,
• parallel treatment,
• integrated treatment.

Sequential treatment

In the sequential model, service users first receive treatment for one disorder, and treatment for the other is deferred until the first disorder is stabilised.

Typically, mental health and drug use treatment networks remain independent and separate, with referrals from one network to another often being the only link between them.

Because co-occurring disorders influence each other, treating one disorder at a time leaves the other condition unaddressed and may reduce the overall effectiveness of the treatment. Consequently, this may result in higher rates of relapse and patient dropout.

Parallel treatment

In the parallel model, simultaneous treatments are provided for the two disorders by two distinct and often separate services.

Although some kind of integration between the two systems may be achieved, policy and organisational issues often prevent effective cooperation between professionals, which may result in fragmented and uncoordinated care, and communication breakdowns between providers. In parallel care models, the responsibility for choosing and following a coherent care plan typically falls on the patients themselves, which can be particularly challenging and potentially inequitable for individuals already at higher risk of treatment drop-out.

Integrated treatment

In the integrated model, both psychiatric and substance use disorders are addressed through simultaneous, integrated and ongoing programmes.

Here, a comprehensive treatment plan is developed to address mental health and substance use disorders simultaneously by a multidisciplinary team. The use of shared treatment plans can help not only to minimise differences in approach among providers but also to ensure that substance use and psychiatric disorders are accurately diagnosed and targeted for stage-specific treatment (SAMHSA, 2010; UNODC, 2022).

Where possible, a clear allocation of responsibilities between services can support smooth collaboration and ensure that both disorders are addressed effectively. While both conditions are treated simultaneously in integrated treatment models, operational clarity on, for instance, which service coordinates particular aspects of care or leads certain interventions, can help avoid confusion and ensure accountability. Regardless of these practical arrangements, care remains fully integrated, with multidisciplinary teams from both services working closely together to provide comprehensive, coordinated treatment.

Integrated treatment seeks to diminish fragmentation, duplication and the risk of ‘falling between the gaps’ arising from sequential or parallel treatment models. It also follows the ‘no wrong door’ approach, whereby people seeking care receive the help they need regardless of where their first contact point with the health system is (UNODC, 2022). However, integrated treatment can be difficult to implement, particularly in fragmented or resource-limited healthcare systems. Patients may also be resistant to changes in their healthcare providers or care delivery methods.

The literature on evidence-based best practices in the treatment of dual disorders supports integrated care models as the standard intervention (EMCDDA, 2015; Fantuzzi and Mezzina, 2020; González-Pinto et al., 2022; Minkoff and Covell, 2021; SAMHSA, 2010). However, there are important limitations due to the limited number of studies evaluating the effectiveness of integrated treatment and the fact that many were undertaken in healthcare contexts dissimilar to those in Europe, such as in the United States (Carrà et al., 2015).

Training

For an integrated treatment system for dual disorders to function properly, it must include a multidisciplinary team of professionals trained and up-to-date with knowledge of both mental and substance use disorders. In this context, targeted workforce development is increasingly recognised as a core element of effective responses to dual disorders, rather than a standalone intervention. By providing ongoing support and training, professionals across both mental health and substance use services remain informed about the latest research and treatment approaches and provide the best possible care for patients with dual disorders.

Training professionals on dual disorders requires a comprehensive approach that includes education on detection and diagnosis, treatment and interdisciplinary collaboration (Avery and Zerbo, 2015; Chambers, 2013). Notably, well-designed training can improve clinical competence in assessing and managing dual disorders, support the development of shared conceptual frameworks and clinical language across mental health and substance use services, and contribute to more consistent and coordinated care.

Importantly, training programmes that integrate clinical knowledge with reflective and experiential learning have been shown to reduce stigmatising attitudes among health professionals, thereby improving therapeutic engagement and quality of care for people with dual disorders (Avery and Zerbo, 2015).

European picture: availability of interventions to address dual disorders

The increased attention given to mental health and dual disorders at the EU policy level was reinforced during the COVID-19 pandemic, reflecting the growing awareness of the complex and interlinked challenges faced by people with dual disorders.

In 2023, the Council of the European Union invited Member States, the European Commission and relevant EU agencies to work together and implement twelve priority measures to strengthen prevention, treatment and coordination for people with co-occurring drug use and mental health disorders (Council of the European Union, 2023).

Availability and coverage

Overall, there are considerable differences in approaches to dual disorders not only between European countries, but also between regions within the same country. In some cases, specific information on treatment services for substance use and mental health disorders is available, while in others, only a general approach is described.

A 2022 mapping of the main approaches to dual disorder treatment among 26 European countries found a majority have some form of service providing integrated care, mostly in urban settings, although coverage remains limited. Some countries have special facilities, including acute inpatient dual disorder units; dual disorder residential communities; and dual disorder programmes in both mental health and drug use outpatient centres, and low-threshold medical services (Fonseca et al., 2026).

While considerable efforts are still required to implement a viable, integrated and effective treatment process and system to address dual disorders, rapid changes are occurring in this area.

Implications for policy and practice

Basics

• Dual disorders consist of the co-occurrence of a substance use disorder and one or more psychiatric disorders in the same individual.
• The systematic early detection and treatment of individuals with dual disorders is crucial.
• It is important that therapeutic approaches to address dual disorders, whether pharmacological, psychological or both, consider both disorders to ensure optimal outcomes.
• It is important to scale up integrated health services for dual disorders to meet current and future demand, improve patient outcomes and strengthen system preparedness.

Opportunities

• There is considerable interest in gaining a better understanding of dual disorders to improve the prognosis of affected individuals and offer better treatment.
• Improved monitoring of the prevalence of mental health disorders in the reporting systems on drug use treatment across Europe, along with better monitoring of substance use disorders in mental health services, will enable a better understanding of dual disorders.
• A comprehensive review and research on early interventions to identify high-risk patients may inform the implementation of effective prevention measures.
• Training staff across service areas in integrated approaches can be implemented immediately and is a critical first step in strengthening the capacity for coordinated care and improving the detection and treatment of dual disorders.
• Time in prison allows for more consistent detection and treatment of dual disorders. Providing care for dual disorders in custodial settings can improve clinical outcomes, may help reduce risk factors associated with recidivism and represents a well-invested use of time and treatment resources.

Gaps

• Better data are needed on the occurrence of dual disorders among people who use drugs and on the use of drugs or the non-medical use of medicines among people with mental health disorders, to better understand the scale of the situation and improve the coverage and adequacy of treatment responses.
• More studies are needed to improve the evidence base for care strategies and pharmacological and psychosocial treatments for patients with dual disorders.
• Further analysis is required to better understand the prevalence and patterns of dual disorders in specific settings, including prisons, and among population groups at higher risk, such as women using drugs with co-occurring post-traumatic stress disorder (PTSD).
• There is a need to establish clear operational responsibilities between mental health and substance use services, to ensure that both services provide integrated care. While evidence on the most effective strategies is still developing, defining how each service coordinates care for each patient can reduce fragmentation and the risk of drop-out.

Further resources

EUDA

• EUDA, 'Comorbidity of mental health and substance use disorders', Topics page, EUDA website.
• EUDA, ‘Spotlight on… comorbid substance use and mental health problems’, 6 November 2023.
• EMCDDA, Torrens, M., Mestre-Pintó, J.-I. and Domingo-Salvany, A., ‘Comorbidity of substance use and mental disorders in Europe’, Insights, Publications Office of the European Union, Luxembourg, 2015.

Other resources

• Council of the European Union, ‘Council conclusions on people having drug use disorders that co-occur with other mental health disorders’, 16112/23, 5December 2023.
• National Working Group for Dual Diagnosis, Model of care for people with mental disorder and co-existing substance use disorder (dual diagnosis), 2023, Health Service Executive.
• United Nations Office on Drugs and Crime (UNODC), ‘Discussion paper– Pre-publication draft– Comorbidities in drug use disorders– No wrong door’, 9March 2022.
• UNODC/ World Health Organization Informal Scientific Network, ‘Informal Scientific Network statement– Managing psychiatric comorbidities in drug use disorders’, 2March 2020.
• World Health Organization, mhGAP intervention guide for mental, neurological and substance use disorders in non-specialized health settings– Version2.0, 2016.

References

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About this page

This miniguide is part of a larger set that together comprises the Health and social responses to drug problems: a European guide. It provides an overview of key aspects related to dual disorders, including service delivery, available evidence and what is happening in Europe. It also considers implications for policy and practice.

Recommended citation: European Union Drugs Agency (2026), Dual disorders: health and social responses, https://www.euda.europa.eu/publications/mini-guides/dual-disorders_en 

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