Drug and alcohol use

What is comorbid drug and alcohol use? 

Drug and alcohol misuse, abuse or dependence are concerns for people with schizophrenia due to the association with poor clinical and social outcomes, including high rates of suicide, HIV, homelessness, aggression and incarceration. Moreover, substance use places additional burden on patients, families, psychiatric services, and government resources due to high rates of treatment non-adherence and relapse.

This topic covers outcomes for people with schizophrenia and comorbid substance use (termed ‘dual diagnosis’).

What is the evidence on outcomes for people with schizophrenia and comorbid drug and alcohol use?

High quality evidence shows a small increase in positive symptoms, but a medium-sized reduction in negative symptoms in people with schizophrenia and any current substance use disorder compared to people with schizophrenia without a current substance use disorder. Moderate to high quality evidence finds patients with any current substance use are also more likely to have depressive symptoms.

Moderate to low quality evidence finds an increased risk of treatment non-adherence, relapse and re-hospitalisation in people with first-episode psychosis and cocaine, opiates, or ecstasy use. Patients with a mixed psychoactive substance use disorder or a cocaine use disorder also show increased extrapyramidal (movement) symptoms, particularly akathisia and tardive dyskinesia compared to patients without a substance use disorder.

For cannabis use, there was a small increase in hospital stay duration in those who continued using cannabis after the onset of psychosis compared to non-users. There was also higher rates of relapse in people who continued cannabis use compared to people who discontinued cannabis use after the first onset of psychosis. Cannabis use was also associated with more suspiciousness and unusual thought content in people at risk of psychosis.

For overall functioning, moderate to high quality evidence finds a small decrease in global functioning in people with psychosis and a current substance use disorder compared to people with psychosis and a former substance use disorder, and decreased functioning in people with a former substance use disorder compared to people with no former substance use disorder.

For cognition, high quality evidence shows a small effect of lower current IQ, and a medium-sized effect of lower premorbid IQ in people with psychosis and current cannabis use compared to people with psychosis without current cannabis use. Moderate quality evidence also finds poorer verbal working memory in those with psychosis currently using cannabis. For people with schizophrenia specifically, moderate to high quality evidence finds a medium-sized effect of better global cognition, processing speed, planning, and visual and working memory in those with any history of cannabis use, but not in those with current cannabis use. Similarly, high quality evidence shows a small to medium-sized increase in global cognition ability, processing speed, planning, visual and working memory, attention, and psychomotor skills in people with psychosis with a polysubstance or cannabis use disorder compared to people with psychosis and no substance use disorder. For people with psychosis and an alcohol use disorder, moderate quality evidence finds more impaired working memory compared to people with psychosis and no substance use disorder.

July 2019

Last updated at: 7:06 am, 31st July 2019
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Fact Sheet Technical Commentary

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Title Colour Legend:
Green - Topic summary is available.
Orange - Topic summary is being compiled.
Red - Topic summary has no current systematic review available.