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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 patients with drug and alcohol use?

High quality evidence shows a small increase in positive symptoms and a medium-sized reduction in negative symptoms in people with schizophrenia and a current substance use disorder compared to people with schizophrenia without a current substance use disorder. Moderate quality evidence suggests patients with current substance use are also more likely to have depressive symptoms. Patients with a mixed psychoactive substance use disorder or a cocaine use disorder show increased extrapyramidal (movement) symptoms, particularly akathisia and tardive dyskinesia compared to patients without a substance use disorder.

High quality evidence shows a small to medium-sized increase in global cognition, processing speed, planning, visual and working memory, attention and psychomotor skills in people with psychosis and a current polysubstance or cannabis use disorder. People with psychosis and a cocaine use disorder showed better attention and psychomotor skills than people with psychosis with no substance use disorder. Conversely, moderate quality evidence suggests more impaired working memory in patients with an alcohol use disorder compared to patients with no substance use disorder.

High quality evidence shows a small effect of longer hospital stays in people who continued cannabis use after onset of psychosis compared to non-users. There is also higher rates of relapse in people who continued cannabis use compared to people who discontinued cannabis use after first onset of psychosis. Moderate to low quality evidence suggests an increased risk of treatment non-adherence, relapse and re-hospitalisation in people with first-episode psychosis and cocaine, opiates, or ecstasy use. Moderate quality evidence suggests 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 in people with former substance use compared to people with no former substance use disorder.

Also see the substance use as a risk factor topic, the topic on rates of substance use in people with schizophrenia (drugs and alcohol, smoking), and the topics on treatments for dual diagnosis  (pharmaceutical and psychosocial).

March 2016

Page last updated: 22:21  6 September 2017

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