Meaning Of Dual Diagnosis

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Dual diagnosis means suffering from a substance/alcohol use disorder and a psychiatric disorder simultaneously [1].

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What Is Dual Diagnosis

Dual diagnosis represents a dual pathology intersection where mental health and substance abuse diagnoses meet. 

The interconnected nature and simultaneous timing of the underlying issues make it difficult to understand and treat the condition fully:

  • Each condition can exacerbate the other, complicating treatment
  • Patients are likely to be rejected by addiction and mental health programmes until one or the other condition is alleviated
  • Patients are likely to be misdiagnosed and not receive the correct treatment [2]
  • Medical professionals in different locations ascribe differing meanings to dual diagnosis, changing treatment priorities and long-term treatment outcomes [3]
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Assumed Attributes Of Dual Diagnosis

Professionals working with dual diagnosis typically assume shared characteristics in dual diagnosis patients:

  • Difficulty identifying dual diagnosis, particularly if medical professionals are not diagnosing two separate conditions
  • Limited academic research resources covering dual diagnosis
  • Lack of standardised definition of dual diagnosis
  • Potential for misdiagnosis when drug/alcohol abuse is not detected in mental health treatment or vice versa [4]
  • Difficulties accessing insurance policies that cover dual diagnosis care: insurers may claim that dual diagnosis care was not medically needed [5]
  • Higher patient complexity and co-morbidity of other issues
  • Higher chronicity of dual diagnosis compared to other acute conditions [6]
  • The high degree of person-centred care necessary
  • The need for completely new or unique therapeutic interventions [7]
  • The need for different professional teams to collaborate more than normal during treatment
  • The long-term, dynamic, and continually changing nature of dual diagnosis symptoms
  • The need for ongoing re-assessment and re-evaluation of patients' needs
  • Possibility of combined medications during treatment causing negative reactions [8]
  • Possibility of medication typically used to treat one disorder exacerbating the other disorder
  • Previously not having received the correct support from either addiction or mental health services [9]

Meaning Of Dual Diagnosis In Professional Assessment Tools


Manual Of

Index (ASI)


Definition Of Dual

One or more mental health and
substance abuse

A drug or alcohol
combined with a mental health

Alcoholism combined with mental illness

How Definition Differs

Considers all
forms of mental health and substance abuse as dual diagnosis

Classes dual
diagnosis and
conditions as the same [11]

Only considers the physical
symptoms of
diagnosis [12]


Severity Of

Assessment Of Dual
Diagnosis (ADD)

Definition Of Dual

Patient must suffer from one or more: Mania, depression, anxiety, PTSD,
substance abuse, somatoform disorders,
dementia, schizophrenia,
personality disorders or eating disorders

How Definition Differs

Primarily focuses on emotional effects of
diagnosis [13]

Highlights specific
conditions that qualify as dual diagnosis [14]

Dual Diagnosis As Defined By Professionals In The Field

Psychiatrists in the field may define dual diagnosis differently from standardised DSM-5 or other definitions:

  • Using a 'working diagnosis' of dual diagnosis even if symptoms do not fit into established criteria to progress with treatment [15]
  • Comparing the severity of mental health disorder to the severity of substance abuse to organise individualised effective care when a joined-up approach is not available
  • Considering co-occurring learning disabilities when considering dual diagnosis [16]

Dual Diagnosis Is Not

Comorbidity/Co-Occurring Disorders Vs Dual Diagnosis

Co-Occurring/Comorbid Disorders

Dual Diagnosis

One disorder followed by another, or
disorders occurring one after another

Each disorder occurs simultaneously

Neither disorder has been caused or triggered by symptoms of the other

Can be caused by symptoms of the other

Sequential treatment not prioritising either disorder

Integrated and simultaneous mental health and substance abuse treatment

Substance Misuse Alone Vs Dual Diagnosis

Dual diagnosis is defined as the presence of a separate psychiatric disorder alongside substance misuse. 

Whereas, substance misuse alone may cause symptoms of psychiatric complaints, but is not a standalone psychiatric disorder.

Complex Mental Health Diagnoses Vs Dual Diagnosis

Complex mental health diagnoses include:

  • Schizophrenia
  • Bipolar disorder
  • Post-traumatic stress disorder
  • Anorexia or bulimia
  • Personality disorders (e.g. multiple personality disorder, borderline personality disorder)

Whereas dual diagnosis is the presence of a mental health disorder and an alcohol or substance use disorder existing simultaneously.


Behavioural Health Diagnoses Vs Dual Diagnosis

A behavioural health disorder is caused by behavioural issues, such as:

  • Substance use disorder
  • Anorexia or bulimia
  • Gambling addiction
  • Sex addiction

Whereas, dual diagnoses as a mental health disorder can be caused by underlying brain chemistry, or genetic factors.

Attempts To Standardise Meaning Of Dual Diagnosis

Attempts to standardise meaning of dual diagnosis have been unsuccessful, leading to distinctions in diagnosis criteria, including:

  • A severe mental health disorder and substance abuse
  • Any form of mental health disorder and drug or alcohol dependency

This lack of universally accepted definition has led to inconsistent care, as medical professionals do not have enough research available to substantiate the effectiveness of different treatments.

Establishing diagnostic criteria for dual diagnosis allows researchers to develop appropriate treatments for different varieties of dual diagnosis [17].

How The Meaning Of Dual Diagnosis Changes According To Setting

Rehab Clinic

In a rehab setting, the meaning of dual diagnosis and co-occurring conditions are synonymous for the purpose of treatment.


The meaning of dual diagnosis in hospitals primarily focuses on mental illness and considers alcohol secondarily.

For example, dual diagnosis treatment focuses on:

  • How alcohol has been used to self-medicate symptoms of mental illness
  • How alcohol has caused mental health disorders being treated as part of dual diagnosis [15]

Research Environment/Academic Papers

The lack of a standard academic definition of dual diagnosis has led to differing meanings of dual diagnoses, such as:

  • Defining dual diagnosis as primarily a severe mental illness combined with secondary substance abuse [18]
  • Defining dual diagnosis as primarily alcohol abuse combined with one or more secondary psychiatric complaints [19]

Insurance Policies

Insurance policies deal with dual diagnosis as separate claims for substance abuse and mental health disorders [20].


Meaning Of Dual Diagnosis In Different Locations

In Canada, dual diagnosis refers to the presence of a learning disability and a psychiatric disorder [21]. 

In the UK and other countries with nationalised healthcare, difficulties arise when accessing joined-up treatment for simultaneous mental health disorders and addiction due to a lack of funding and service availability. 

Countries with diverse ethnic backgrounds experience:

  • Language barriers affecting patient's understanding of dual diagnoses
  • Religious or cultural stigma of addiction/mental health disorders affects treatment accessibility
  • Different cultures are offended by personal questions and do not continue treatment [22]

Patient Diagnosed With
Dual Diagnosis in USA

Patient Diagnosed With
Dual Diagnosis in UK

Definition Of Dual  Diagnosis

Any form of mental illness 
and combined alcohol or  drug dependency

Severe mental illness and 
combined drug  dependency

Service Availability

NHS treatment - going to 
specialists causes
lack of continuity of care

Cultural Attitudes Towards Mental Illness

Stigma endorses secret 
drinking and not getting 
treatment [23]

Public mental health
campaigns reduce stigma
and increase accessibility of treatment [24]

Long-Term Treatment 

12% receive integrated 
dual-diagnosis treatment  [25]

50% receive integrated  dual diagnosis treatment  [26]

Legislation & Regulation May Change How Dual Diagnosis Is Defined

Differing regulations or oversight in policies can influence how dual diagnosis is defined due to:

  • Medical professionals using the ICPC-2 finding that having three appointments and physical testing causes oversight of dual diagnosis symptoms [27]
  • Alcohol or mental illness scales used in regulations not correctly diagnosing dual diagnosis
  • The Global Disease Burden considers neurological disorders (e.g. Parkinson's and epilepsy) as part of dual diagnosis [28]
  • The North American Nursing Diagnosis Association (NANDA) uses a nursing diagnosis that focuses on the physical response to illness that informs intervention, this may cause polydrug use to be considered the cause of symptoms and not dual diagnosis [29]

How The Meaning Of Dual Diagnosis Changes Treatment Priorities

The meaning given to dual diagnosis changes:

  • What is considered a dual diagnosis - is Parkinson's or epilepsy included? Are all mental health disorders included or just those considered severe?
  • How treatment is prioritised - whether mental health disorder or addiction is treated first
  • What aspects of treatment are available - e.g. secondary diagnosis of mental health disorders due to nursing diagnosis leads to longer waiting lists for treatment
  • Access to differing medication types or regimens - these may not be in line with specific medical professional's definition of dual diagnosis and therefore not prescribed

Order And Sequence Of Dual Diagnosis Treatment May Change

The order and sequence of dual diagnoses may change due to:

  • Initially using nursing diagnosis may cause the medical professionals to miss underlying causes or the possibility of multiple diagnoses causing symptoms that are only noticed sequentially
  • Initially using the ICPC-2 to focus on physical tests for symptoms may miss psychological symptoms that alter diagnosis

Dual Diagnosis Meaning Can Impact Patient Care Plans

Elements Of A Care Plan

Dual Diagnosis Meaning A **Severe** Mental Health Disorder And Substance Abuse

Dual Diagnosis Meaning
**Any** Mental Health
Disorder And Alcohol Or
Drug Dependency

Current lifestyle and history of abuse

May overlook less  advanced mental health  issues that affect  substance abuse

Focuses on co-occurring 
symptoms of mental illness  and addiction

Psychiatric care needs

May not consider link 
between less advanced 
mental health disorders  (e.g. anxiety and  depression) and substance  abuse when planning  psychiatric care needs

Will consider the link between all mental health disorders and alcohol and drug dependency to inform psychiatric care needs

Not classing patients as dual diagnosis could mean not believing they are sufficiently motivated to attend rehab

Will be aware that complex
cases of dual diagnosis
cause patients to struggle to be motivated to seek help

Risk assessment

Misdiagnosis of dual
diagnosis could cause risks
to be unaccounted for

Considers risks to self and
others when starting

Impact Of Differing Dual Diagnoses Definitions, On Patients' Lives


Dual Diagnosis Diagnosed Via DSM-5

Dual Diagnosis Diagnosed Via ICD

Differing definition of dual

Focused on classifying
mental health disorders,
leading to a quick diagnosis

Classifies all forms of
disorders, leading to a longer diagnosis/diagnosis of physical symptoms and not mental health

Family and social support

Social support may not be
relevant when needed due to longer diagnosis

Experience of stigma

Some feel stigmatised due to labelling mental health

Using codes for symptoms
and diagnoses to avoid

Treatment by other medical professionals

Classification may not be
understood by other medical professionals, disrupting treatment

Classification is understood by other medical professionals

Access to care and support

Immediate access to
joined-up care

Can be delayed access due
to more extended diagnosis

Self esteem and psychological impact of
diagnosis affecting
relationships with others

Labelling mental health
disorders leads to lower self esteem and negative
relationships with others

Inclusive view of health
improves self esteem and 
encourages better 
relationships with family


Individualised aftercare plan using DSM-5 to track
progress and adjust plan if

Aftercare plan is not as
detailed and uses holistic

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About the author

Harriet Garfoot

Harriet Garfoot BA, MA has an Undergraduate degree in Education Studies and English, and a Master's degree in English Literature, from Bishop Grosseteste University. Harriet writes on stress & mental health, and is a member of the Burney Society. Content reviewed by Laura Morris (Clinical Lead).

Last Updated: March 27, 2024