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Identifying co-occurring disorders

Prevalence of co-occurring substance use and mental health problems

The prevalence of a substance use disorder in people with a psychiatric disorder is high. In Canada, 16.1 per cent of people diagnosed with a psychiatric disorder during their lifetime experienced a substance use problem in the preceding year (Statistics Canada, 2002). The lifetime prevalence of psychiatric disorders in people with a current alcohol problem is 27.5 per cent (Statistics Canada, 2002).

Relationship between mental health and substance use problems

Mental health and substance use problems interact in various ways:

  • Alcohol and other drugs are effective short-term anxiolytics and are often used to self-medicate symptoms of anxiety.
  • People with alcohol or other drug addiction often attribute withdrawal symptoms to anxiety.
  • Alcohol and other drugs tend to exacerbate co-existing primary psychiatric disorders. For example, cannabis worsens symptoms of schizophrenia and can precipitate a psychotic episode.
  • Alcohol is often responsible for depressive symptoms (alcohol-induced mood disorder) in people with alcohol dependence.
  • All of the major drugs can cause substance-induced psychiatric disorders, particularly mood and anxiety disorders.
  • People with primary psychiatric disorders can develop substance-induced disorders. For example, someone with an anxiety disorder can develop alcohol-induced depression.
  • Substance use can interfere with treatment of the primary psychiatric disorder in various ways:
    • People who use substances are less likely to adhere to psychiatric pharmacotherapy.
    • Substances may interact with psychiatric medications.
  • Substance use can contribute to behavioural problems and interpersonal difficulties.

Concurrent disorders

A co-existing substance use disorder and primary psychiatric disorder is known as a concurrent disorder.

Given the high rates of co-occurring mental health and substance use problems, all patients presenting with a mood, anxiety or psychotic disorder should be screened for substance use, and all patients with a substance use disorder should be screened for depression, anxiety, psychosis and a history of trauma.

Substance-induced psychiatric disorders

A psychiatric disorder is more likely to be substance induced if:

  • the psychiatric symptoms developed during or within a month of substance intoxication or withdrawal
  • the substance used is known to cause symptoms of anxiety, depression or psychosis
  • the symptoms resolve with abstinence
  • the symptoms cannot be better explained by a disorder that is not substance induced.

Table 1: Clinical features of primary and substance-induced disorders


Suicide risk with co-occurring disorders

People with substance-induced disorders have a higher risk for suicide, particularly during acute intoxication and withdrawal. These patients should be carefully assessed, observed and, if necessary, admitted to hospital.

Often a patient's mental state improves within 24 to 48 hours of abstinence, which helps to distinguish between substance-induced symptoms and primary psychiatric problems.

Antidepressants and intensive treatment for substance dependence should be initiated in patients with concurrent depression.