Concurrent Disorders

Concurrent disorders describes a condition in which a person has both a mental illness and a substance use problem. This term is a general one and refers to a wide range of mental illnesses and substance use disorders. For example, someone living with schizophrenia who also engages problematic cannabis use has a concurrent disorder, as does an individual who lives with chronic depression and who also engages in problematic alcohol use. Treatment approaches for each case could be quite different.Another term for concurrent disorder is comorbidity. In the United States, the terms dual diagnosis, dual disorder, or mentally ill chemical abuser are used to refer to concurrent disorder.1 In Canada, dual diagnosis usually refers to someone with a mental disorder and a co-occurring developmental disability. (For more information, see Dual Diagnosis.)

It is challenging to determine conclusively how many people have a concurrent disorder because existing studies examine different populations and utilize differing screening tools. Further, people with concurrent disorders are frequently misidentified, as diagnosis can be more difficult because one disorder can mimic another. Relapse rates for substance use are higher for people with a concurrent mental disorder, as are the chances that symptoms of mental illness will return for those with a concurrent substance use problem. Depending on the setting, prevalence rates for concurrent disorders have been found to range from 20 to 80 percent.2

What is known conclusively, however, is that people with mental illness have much higher rates of addiction than people in the general population. Similarly, individuals with an addiction have much higher rates of mental illness than people in the general population. One large US study found that approximately a third of people with a mental or alcohol disorder had a concurrent disorder, and half of the people with drug problems had a mental disorder. A smaller study in Edmonton, Alberta had similar findings. In this study, almost a third of mentally ill individuals also had a substance use problem, almost a third of those with alcohol dependency also had a psychiatric diagnosis, and among illicit drug users, almost half had a mental illness.3

1Centre for Addiction and Mental Health, “Answers to Common Questions on Concurrent Disorders,” Journal of Addiction and Mental Health, September-October 1998, 16.
2Centre for Addiction and Mental Health, “People with Concurrent Disorders,” in Virtual Resource for the Addiction Treatment System, Section 3: Special Populations.
3Centre for Addiction and Mental Health, “Answers to Common Questions on Concurrent Disorders,” op. cit.