Dual Diagnosis: Unravelling the Complexity of Co-occurring Disorders
Dual diagnosis, also known as co-occurring disorders, describes the presentation of both a mental health disorder and a substance use disorder at the same time. This presents special challenges in diagnosis and treatment and requires an integrated approach to deal with the complicated relationship between the two. Understanding the relationship between mental health and substance use is key to intervention and long term management. The Institute of Behavioural Medicine acknowledges the complicated biological, psychological and social factors involved in dual diagnosis.
Understanding the Interplay: Mental Health and Substance Use Disorders

The overlap between the presentation of mental health disorders with substance use disorders is likely not a coincidence, and we now know that several factors play into this complex relationship. Indeed, many people with mental health disorders seem to turn to substances as a way to self-medicate for symptoms like anxiety, depression or psychosis. Conversely, substance use is known to exacerbate mental health conditions creating a vicious cycle of dependence, mental health decline, and increased substance use.
Co-occurring risk factors like genetic predisposition, adverse childhood experiences and trauma can also increase vulnerability to both mental health and substance use disorders. Trauma plays a big role in susceptibility as people may use substances to cope with the emotional pain and distress of traumatic experiences. The Diagnostic and Statistical Manual of Mental Disorders (DSM-5) has specific criteria for diagnosing mental health and substance use disorders, nevertheless, diagnosis of mental health conditions requires a thorough clinical assessment.
Prevalence and Identification of Dual Diagnosis
Research has demonstrated a high prevalence of dual diagnosis Indeed, according to the 2022 National Survey on Drug Use and Health (NSDUH), over 21.5 million adults and nearly one million adolescents (ages 12-17) in the USA were found to have a co-occuring Mental Health Issues and Substance Use Disorder, with fewer than half receiving some form of treatment.
Dual Diagnosis can be difficult to identify as symptoms of one disorder can mask or mimic the other. For example, symptoms of depression can be attributed to substance use alone, or anxiety symptoms can appear similar to withdrawal. A full assessment that includes a detailed history of mental health symptoms, substance use patterns and any co-occurring medical conditions is key to accurate diagnosis. Screening tools like the Addiction Severity Index (ASI) and the Mini-International Neuropsychiatric Interview (MINI) can help identify potential co-occurring disorders.
The Neurobiological Basis of Co-occurring Disorders
The neurobiology of Dual Diagnosis is complex and involves several different brain regions and neurotransmitters. Both mental health and substance use disorders affect the circuits in the brain that handle reward, motivation and impulse control.
Substance use can alter dopaminergic signalling pathways, mental health disorders can disrupt the balance of serotonin and alter noradrenergic signalling Research suggests Dual Diagnosis involves dysfunction in fronto-limbic neural pathways and circuitries that regulate reward, impulse control and emotional processing. This includes impairments in the prefrontal cortex , which affects decision making, and increases susceptibility to cravings and relapse. Understanding the neurobiological mechanisms that underlie Dual Diagnosis will be essential for the development of targeted interventions that tackle both shared and disparate neural pathways that contribute to mental health and substance use disorders. .
Diagnostic Criteria and Assessment Methods for Dual Diagnosis

Accurate diagnosis is essential for effectively treating Dual Diagnosis. Clinicians must assess whether an individual meets the criteria for both a mental health disorder and a substance use disorder, as well as the severity of each. The DSM-5 provides specific diagnostic criteria for mental health and substance use disorders including criteria for severity, duration and functional impairment.
A comprehensive clinical assessment for Dual Diagnosis usually involves clinical interviews that allows the clinician to gather information about the individual’s history, symptoms and functional impairments, self-report questionnaires such as the Beck Depression Inventory (BDI) and Addiction Sensitivity Index (ASI), structured diagnostic interviews including the Mini-International Neuropsychiatric Interview (MINI) as well as the collection of collateral information from family members or other healthcare providers that can provide valuable insight into the individual’s behavior and functioning from others
Evidence-Based Therapeutic Approaches for Dual Diagnosis
For Dual Diagnosis treatment you need an integrated approach that treats both the mental health and substance use disorders at the same time. Integrated treatment models combine psychological, pharmacological and social interventions to promote recovery and overall functioning. Several evidence based therapeutic approaches have been shown to be effective for Dual Diagnosis.
Cognitive Behavioural Therapy (CBT) helps individuals identify and change maladaptive thoughts and behaviours that contribute to mental health and substance use problems. Motivational Interviewing (MI) is a client centred approach that helps individuals explore their ambivalence about change and increase their motivation to engage in treatment. Integrated Group Therapy (IGT) provides a space for individuals with Dual Diagnosis to share their experience, learn coping skills and develop social support.
Integrated Treatment Models: Combining Therapies for Optimal Outcomes
Integrated treatment models are considered the gold standard, designed to give a person with a Dual Diagnosis comprehensive and coordinated care between mental health and addiction specialists. These models involve a team of professionals including psychiatrists, psychologists, social workers and addiction counsellors who work together to develop and implement individualised treatment plans. Integrated treatment models may include individual therapy, group therapy, medication management and case management services.
The key principles of integrated treatment are whole person focus, collaboration in treatment planning and ongoing support and monitoring. Integrated treatment models aim to address the underlying causes of the mental health disorder and the substance use disorder as well as the social, vocational and educational challenges.
Navigating the Challenges in Dual Diagnosis Treatment
Dual Diagnosis is tricky. People with co-occurring disorders are harder to engage in treatment because of denial, ambivalence and impaired cognitive functioning. They are more likely to relapse because of the interplay between mental health and substance use symptoms.

Another problem is the fragmentation of services. People with Dual Diagnosis are seen by different providers who don’t communicate or coordinate their care. That leads to inconsistent treatment and bad outcomes. Overcoming these challenges requires a collaborative and integrated approach with clear communication and coordination between all providers involved in their care.
Long-Term Management and Relapse Prevention Strategies
Recovery from Dual Diagnosis is a long term process that requires ongoing support and monitoring. Relapse is common but doesn’t mean failure, rather it provides an opportunity to learn from experiences and adjust treatment plans. Relapse prevention strategies are a key part of long term management.
These may include developing coping skills to manage stress and cravings, identifying triggers and high risk situations and building a strong support network. Regular follow up appointments with your healthcare provider are also important to monitor symptoms, adjust medication and provide ongoing support. With the right treatment and support people with Dual Diagnosis can achieve real recovery and live fulfilling lives.
Highlands Recovery recognises the complexity of dual diagnosis and uses behavioural medicine principles to address the biological, psychological and social aspects. By providing a structured environment and evidence based therapies Highlands Recovery aims to support individuals in achieving long term recovery from co-occurring disorders. Our approach is individualised to each client’s needs to promote self directed health and long term wellbeing.
Reviewed by: Dr. Emma Bardsley

Dr Emma Bardsley is a neuroscientist with a PhD from Oxford and a post doctorate from Auckland University, along with an undergraduate degree in Pharmacology from King’s College London. She has lectured extensively on neuroscience, physiology, and pharmacological interventions, bridging foundational research and its clinical applications. With a strong record of publications in high-impact journals and extensive experience in scientific writing, editing, and peer review, she excels at translating complex research into practical insights. Based in New Zealand and collaborating internationally, Emma is dedicated to advancing understanding and treatment in the fields of trauma, addiction, and recovery.
References
Drake, R.E. and Wallach, M.A., 2000. Dual diagnosis: 15 years of progress. Psychiatric services, 51(9), pp.1126-1129. https://doi.org/10.1176/appi.ps.51.9.1126
Kessler, R. C. (2004). The epidemiology of dual diagnosis. Biological psychiatry, 56(10), 730-737.https://doi.org/10.1016/j.biopsych.2004.06.034
Mueser, K.T., Drake, R.E. and Wallach, M.A., 1998. Dual diagnosis: a review of etiological theories. Addictive behaviors, 23(6), pp.717-734. https://doi.org/10.1016/S0306-4603(98)00073-2
Tiet, Q.Q. and Mausbach, B., 2007. Treatments for patients with dual diagnosis: a review. Alcoholism: Clinical and Experimental Research, 31(4), pp.513-536. https://doi.org/10.1111/j.1530-0277.2007.00336.x
Substance Abuse and Mental Health Services Administration (SAMHSA). 2022 National Survey on Drug Use and Health: Main Highlights https://www.samhsa.gov/data/sites/default/files/reports/rpt42731/2022-nsduh-main-highlights.pdf