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Dual Diagnosis

In Canada, dual diagnosis usually refers to an individual with a mental illness and a co-occurring developmental disability.¹

An individual with a developmental disability has significantly below average intellectual functioning, which is also accompanied by considerable limitations in their adaptive functioning or life skills. People with persistent developmental disorders (such as autism) are often included under the umbrella of developmental disabilities, even if their IQ approaches average. Approximately 1 to 3 percent of Canadians have a developmental disability.²

Prevalence rates for dual diagnosis are difficult to identify because studies apply differing criteria in defining developmental disabilities and mental health issues. For example, definitions of developmental disability often use varying criteria in terms of severity of the disability or IQ level, and similarly, there is an inconsistency in how mental health problems are defined in this population. It is generally agreed, however, that individuals with developmental disabilities are three to four times more likely to develop emotional, behavioural and psychiatric difficulties than the general population.³

Related Resources

• Dual Diagnosis: People with Developmental Disability and Mental Illness – Falling through the Cracks (1998)
  A backgrounder on the issue of dual diagnosis, including the prevalence of dual diagnosis, a discussion of the responsibility for the care for those experiencing these problems, and an overview of the specific issues at the systems, program/service and individual/family levels.
• CMHA Ontario Position Paper Respecting Dual Diagnosis (June 1998)
  This paper addresses the complex needs of individuals with dual diagnosis, particularly their need for comprehensive, integrated and appropriate supports to be accessible.
• Dual Diagnosis in Ontario's Psychiatric Hospitals: Quantitative and Qualitative Findings (November 2006)
  Presentation from the 2006 Making Gains conference.

Links (Ontario)

• Dual Diagnosis Paper (Susan Morris, Psychiatric Patient Advocate Office, 2003)
• Dual Diagnosis: Resources for Professionals (Centre for Addiction and Mental Health)
• Dual Diagnosis: Resources for Families and Significant Others (Centre for Addiction and Mental Health)
• National Association for the Dually Diagnosed, Ontario Chapter
• University of Western Ontario, Development Disabilities Division

Links (International)

• National Association for the Dually Diagnosed (USA)
• Learning about Intellectual Disabilities and Health (UK)
• Connects: Mental Health and Learning Disabilities Portal (UK)

1. In the United States, however, and sometimes even in Canada, dual diagnosis is the term used to describe concurrent disorder, the co-occurrence of substance use and mental illness. For more information, see Concurrent Disorders.
2. Centre for Addiction and Mental Health, "Common Questions about Dual Diagnosis," Journal of Addiction and Mental Health, May-June 2002, 13.
3. Ibid.