Co-Occurring Mental Health Disorders: Considerations for Clinicians

This article defines co-occurring disorders, examines the most common combinations which occur, and provides guidance on best practices for clinical care.

Related articles: The Transdiagnostic Model in Mental Health Care, Trauma-Informed Practice: Fundamentals for Therapists, Ethical Decision-Making in Mental Health.

Introduction

Co-occurring mental health disorders, also known as comorbid or dual-diagnosis disorders, refer to the simultaneous presence of two or more mental health conditions in an individual. These disorders often complicate clinical presentations, making assessment, diagnosis, and treatment more challenging. However, understanding the complexities of co-occurring disorders is crucial for clinicians seeking to provide comprehensive and effective care.

This article explores the definition of co-occurring disorders, examines the most common combinations, and provides evidence-based guidance on best practices for treatment. Case scenarios and practical tools are included to enhance clinical application.

Defining co-occurring mental health disorders

Co-occurring disorders are defined as the presence of at least two mental health conditions in one individual, where each disorder meets the diagnostic criteria independently (American Psychiatric Association [APA], 2022). These conditions can include mood disorders, anxiety disorders, substance use disorders (SUDs), and personality disorders, among others. The interplay between co-occurring conditions can exacerbate symptoms, reduce treatment adherence, and complicate prognosis.

Prevalence of co-occurring mental health disorders

Co-occurring disorders are highly prevalent. According to the National Institute on Drug Abuse (NIDA, 2018), approximately 50% of individuals with a mental illness will experience a substance use disorder at some point in their lives, and vice versa. Similarly, anxiety disorders frequently co-occur with depressive disorders, with an estimated 60% overlap (World Health Organization [WHO], 2017).

Common co-occurring mental health disorders

Depression and anxiety

Depression and anxiety are among the most frequently co-occurring mental health disorders. Major Depressive Disorder (MDD) is characterised by persistent sadness, loss of interest, and cognitive and physical symptoms, while anxiety disorders encompass conditions like Generalised Anxiety Disorder (GAD), panic disorder, and social anxiety disorder. The shared neurobiological pathways, such as dysregulation in the hypothalamic-pituitary-adrenal (HPA) axis, contribute to their co-occurrence (Young, Abelson, & Cameron, 2004).

Statistics

Approximately 50% of individuals diagnosed with depression also meet the criteria for an anxiety disorder (Kessler et al., 2007).

A case example

A 35-year-old woman presents with persistent feelings of hopelessness, fatigue, and difficulty concentrating. Upon further exploration, she also describes excessive worry about her job and frequent panic attacks. A dual diagnosis of MDD and GAD is made, and an integrative treatment plan is formulated.

Substance use disorders and post-traumatic stress disorder (PTSD)

The relationship between SUDs and PTSD is bidirectional. Individuals with PTSD may use substances as a maladaptive coping mechanism, while those with SUDs are at increased risk of trauma exposure. Both conditions involve dysregulated stress responses and impaired emotional regulation (Roberts et al., 2022).

Statistics

Research indicates that 20-40% of individuals with PTSD also have an SUD (SAMHSA, 2024a).

A case example

A 28-year-old veteran reports nightmares, hypervigilance, and alcohol dependence. Assessment reveals that alcohol is used to suppress intrusive memories. Treatment involves trauma-focused therapy and motivational interviewing to address both conditions.

Related reading: Case Study: Healing from Trauma as a Soldier.

Bipolar disorder and substance use disorders

Bipolar disorder (BD) involves alternating episodes of mania and depression. The impulsivity and disinhibition during manic phases often lead to substance misuse. Conversely, substances can trigger or exacerbate mood episodes (Swendsen et al., 2000).

Statistics

Approximately 60% of individuals with bipolar disorder will develop an SUD during their lifetime (Merikangas et al., 2011).

A case example

A 42-year-old man with a history of erratic behaviour and depressive episodes reports recent cocaine use. A diagnosis of BD and cocaine use disorder is established, and the treatment plan includes mood stabilisers and contingency management.

Effective treatments for co-occurring mental health disorders

Effective treatment for co-occurring disorders involves an integrated approach that addresses all conditions concurrently. Key principles include:

Comprehensive assessment

Comprehensive assessment is the foundation of effective treatment for co-occurring disorders. Assessment tools are invaluable in identifying the presence and severity of multiple conditions, as well as their interplay. Using standardised tools ensures consistency, objectivity, and accuracy in diagnosis.

Additionally, combining multiple assessments can help clinicians capture the nuanced interactions between disorders and tailor interventions accordingly. Regular re-assessment during the treatment process can monitor progress and guide adjustments to the care plan.

Commonly used assessment tools include:

• Structured Clinical Interview for DSM-5 Disorders (SCID-5): Useful for diagnosing a range of mental health disorders.
• Alcohol Use Disorders Identification Test (AUDIT): Screens for alcohol use.
• Drug Abuse Screening Test (DAST): Evaluates drug use and its consequences.
• PTSD Checklist for DSM-5 (PCL-5): Assesses PTSD symptoms.
• Beck Depression Inventory (BDI): Measures the severity of depressive symptoms.
• Generalised Anxiety Disorder-7 (GAD-7): Screens for anxiety.
• Mood Disorder Questionnaire (MDQ): Identifies symptoms of bipolar disorder.
• WHO Disability Assessment Schedule (WHODAS 2.0): Assesses functional impairments.
• Personality Inventory for DSM-5 (PID-5): Assesses maladaptive personality traits.

During initial assessments, clinicians should obtain a detailed history of symptoms, substance use, trauma, and functional impairments. Collateral information from family members may also be valuable. Comprehensive assessment helps clinicians identify underlying conditions that might otherwise go unnoticed, ensuring a more holistic treatment plan.

Evidence-based therapies

Evidence-based therapies provide a structured and scientifically validated approach to managing co-occurring disorders. By addressing the unique symptoms and challenges posed by each condition, these therapies help clients develop coping mechanisms, improve emotional regulation, and enhance overall functioning. Combining these therapies with an integrated care plan ensures that the interplay between disorders is effectively managed, ultimately promoting sustained recovery.

Following are examples of commonly used evidence-based therapies:

• Cognitive-behavioural therapy (CBT): CBT is highly effective for treating anxiety, depression, and SUDs. It targets maladaptive thought patterns and promotes healthy coping mechanisms (Beck et al., 2024).
• Trauma-focused interventions: For PTSD and SUD co-occurrence, treatments such as Eye Movement Desensitisation and Reprocessing (EMDR) and Trauma-Focused CBT are recommended (Shapiro, 2022).
• Medication-assisted treatment (MAT): Medications like buprenorphine or naltrexone can manage cravings and withdrawal symptoms in SUDs, while antidepressants or mood stabilisers address underlying mental health conditions (SAMHSA, 2024b).
• Dialectical behaviour therapy (DBT): DBT is particularly beneficial for co-occurring borderline personality disorder and SUDs, focusing on emotion regulation and distress tolerance (Linehan, 2014).
• Integrated care models: Integrated care involves multidisciplinary teams that deliver coordinated treatment for both mental health and substance use disorders. The Collaborative Care Model (CoCM) is one such approach, combining primary care providers, mental health specialists, and care managers (Woltmann et al., 2012).

An example of clinical application and integration of evidence-based therapies is a clinic that provides medication-assisted treatment for opioid use disorder with cognitive-behavioural therapy for depression, offering patients a seamless treatment experience.

Practical considerations for clinicians

Practical considerations play a pivotal role in ensuring successful outcomes for individuals with co-occurring disorders. Clinicians must navigate the complexities of overlapping symptoms, treatment priorities, and the challenges of engagement and adherence. A nuanced understanding of these factors can enhance the therapeutic alliance and optimise care delivery.

• Early identification and intervention: Early recognition of co-occurring disorders is critical. Clinicians should maintain a high index of suspicion when clients present with complex or refractory symptoms.
• Tailored treatment plans: Treatment plans should be individualised, considering the severity and interplay of conditions, patient preferences, and social determinants of health.
• Addressing stigma: Stigma can deter individuals from seeking help. Clinicians should create a non-judgmental environment and provide psychoeducation to reduce self-stigma.
• Continuous monitoring and adjustment: Co-occurring disorders often require long-term management. Regularly reassessing symptoms and treatment efficacy is essential.

Conclusion

Co-occurring mental health disorders present unique challenges but also opportunities for meaningful intervention. By employing comprehensive assessments, evidence-based treatments, and integrated care models, clinicians can improve outcomes for individuals navigating the complexities of dual diagnoses. Awareness, empathy, and ongoing professional development are key to mastering the intricacies of co-occurring disorders in clinical practice.

Key takeaways

• Co-occurring mental health disorders involve the simultaneous presence of two or more conditions, often complicating diagnosis and treatment.
• Depression, anxiety, PTSD, SUDs, and bipolar disorder are among the most common co-occurrences.
• Integrated care models and evidence-based therapies such as CBT, DBT, and MAT are essential for effective treatment.
• Early identification, tailored interventions, and regular monitoring enhance clinical outcomes.

References

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• National Institute on Drug Abuse. (2018). Common comorbidities with substance use disorders. NIDA. American Journal of Psychiatry, 178(10), 987-995.
• Roberts, N. P., Lotzin, A., & Schäfer, I. (2022). A systematic review and meta-analysis of psychological interventions for comorbid post-traumatic stress disorder and substance use disorder. European journal of psychotraumatology, 13(1), 2041831. https://doi.org/10.1080/20008198.2022.2041831
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• Substance Abuse and Mental Health Services Administration (SAMHSA). (2024a). Treatment improvement protocol (TIP) series, TIP 63: Medications for Opioid Use Disorder. SAMHSA.
• Substance Abuse and Mental Health Services Administration (SAMHSA). (2024b). Substance use disorder treatment ptions. SAMHSA. Retrieved on 28 January 2025, from: https://www.samhsa.gov/substance-use/treatment/options 
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