Substance use
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Substance use

How is substance use related to schizophrenia?

Various lines of evidence suggest an association between substance use and psychosis. Experimental studies and surveys of users provide evidence that cannabis and amphetamine use can produce transient, and usually mild, psychotic experiences or recurrence of psychotic symptoms in individuals with a history of psychosis. Further, neuroimaging studies have found clear similarities between functional networks impaired by cannabis use and those known to be implicated in the pathogenesis of schizophrenia.

What is the evidence for substance use as a risk factor for schizophrenia?

Tobacco

Moderate quality evidence finds a small to medium-sized increased risk of developing schizophrenia in smokers versus non-smokers. There is also a small increased risk of developing schizophrenia after exposure to tobacco smoke prenatally.

Moderate to low quality evidence finds people with first-episode psychosis smoked tobacco for an average of 5.3 years prior to their first psychotic episode. There is also an earlier age of psychosis onset in smokers compared to non-smokers.

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 for a diagnosis of any psychotic disorder, with increased use increasing the risk of psychosis.

A small, but non-significant association was found between cannabis use and transition to psychosis in people with subclinical psychotic symptoms, with lifetime cannabis use rates in that group being around 49%. Further, 34% of people diagnosed with a cannabis-induced psychosis developed schizophrenia at follow-up (mean 4 years). Initiation of cannabis use is around 6-7 years prior to the onset of psychosis.

Other substances

Moderate quality evidence finds a medium-sized increase in the rates of subclinical psychotic symptoms in people with alcohol or other drug use. Around one-quarter of people with a substance-induced psychosis had a follow-up diagnosis of schizophrenia (mean follow-up 4 years). The rates were highest for cannabis (34%), hallucinogens (26%), and amphetamines (22%), and lowest for opioids (12%), alcohol (10%), and sedatives (9%).

August 2020

Last updated at: 2:49 am, 28th August 2020
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