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 as a risk factor for schizophrenia?

Tobacco
Moderate quality evidence finds the prevalence of smoking in people with first-episode psychosis is around 60%. Moderate to low quality evidence suggests people with first-episode psychosis smoked tobacco for an average of 5.3 years prior to the first psychotic episode. Compared to general population smoking rates, there is a large effect of more smoking in males with schizophrenia, and a medium-sized effect of more smoking in females with schizophrenia. There is also an earlier age of psychosis onset in smokers compared to non-smokers. Compared to males with other mental illnesses, there is a medium-sized effect of more smoking in males with schizophrenia, with no significant differences between females.

Cannabis
High quality evidence shows there is an increased risk of psychotic symptoms with cannabis use. Moderate to high quality evidence suggests this is a dose-dependent relationship for psychotic symptoms, or a diagnosis of any psychotic disorder. Moderate to high quality evidence suggests prevalence of cannabis use in people with first-episode psychosis is around 34-38%. Initiation of cannabis use is around 6-7 years prior to onset of psychosis, and continuation of cannabis use declines after treatment. Moderate to low quality evidence indicates a relationship between cannabis use and increased relapse or re-hospitalisation, and less treatment adherence in people with schizophrenia or psychotic symptoms.

Other substances
Moderate quality evidence suggests a medium-sized increase in prevalence and incidence of subclinical psychotic symptoms in people with alcohol or other drug use.

March 2019

Last updated at: 5:09 am, 16th March 2019
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Fact Sheet Technical Commentary

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