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Substance use

How is substance use relevant to schizophrenia?

Substance use is more common in people with schizophrenia than in the general population.

What is the evidence for substance use?

High quality evidence shows there is an increased risk of any psychotic symptom or disorder (including schizophrenia) in people who use cannabis. Moderate to high quality evidence suggests this relationship is dose-dependent; increased use of cannabis is associated with increased risk of psychosis.

Moderate quality evidence suggests the prevalence of cannabis use in people with first-episode psychosis is around 33-38%, and initiation of cannabis use is around 6-7 years prior to onset of psychosis. Cannabis use tends to decline with treatment, but with continuing use, there is an increased risk of relapse or re-hospitalisation, and less adherence to treatment.

Moderate to low quality evidence suggests the prevalence of tobacco smoking in people with first-episode psychosis is around 57%. There is a medium-sized increased risk of psychotic disorders, and an earlier age of psychosis onset, in tobacco smokers compared to non-smokers. People with first-episode psychosis smoked tobacco for an average of 5.3 years prior to their first psychotic episode. Males with schizophrenia show higher rates of lifetime tobacco smoking than males with other mental illnesses, with no differences in tobacco smoking rates in females with different mental disorders.

Moderate to low quality evidence suggests there are increased rates of subclinical psychotic symptoms (e.g. pseudohallucinations) or other perceptual disturbances in people who use alcohol or other drugs.

Also see the Course and Outcomes drug and alcohol use topic, the Living with Multiple Conditions drug and alcohol use topic, the Psychosocial Treatments for dual diagnosis topic, and the Pharmaceutical Treatments for dual diagnosis topic.

March 2017

Page last updated: 23:47  6 September 2017

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