Cannabis and psychosis: what causes what?

Abstract

Converging lines of evidence suggest that cannabinoids can produce a full range of transient schizophrenia-like positive, negative and cognitive symptoms. Cannabinoids also produce some psychophysiological deficits also known to be present in schizophrenia. It is also clear that, in individuals with an established psychotic disorder, cannabinoids can exacerbate symptoms, trigger relapse, and have negative consequences on the course of the illness. Increasing evidence suggests that early and heavy cannabis exposure may increase the risk of developing a psychotic disorder such as schizophrenia. The relationship between cannabis exposure and schizophrenia fulfills some, but not all, of the usual criteria for causality. However, most people who use cannabis do not develop schizophrenia, and many people diagnosed with schizophrenia have never used cannabis. Therefore, it is likely that cannabis exposure is a “component cause” that interacts with other factors to “cause” schizophrenia or other psychotic disorders, but is neither necessary nor sufficient to do so alone. Further work is necessary to identify the factors that underlie individual vulnerability to cannabinoid-related psychosis and to elucidate the biological mechanisms underlying this risk.

The adverse health effects of synthetic cannabinoids with emphasis on psychosis-like effects

“…It has been claimed that early cannabis use may lead to schizophrenia (Andreasson et al, 1987; Arendt et al, 2005; Arseneault et al, 2002; Dragt et al, 2012; Large et al, 2011; Martinotti et al, 2012; Moore et al, 2007; Van Os et al, 2002), although a causal relationship was never established (Castle, 2013; Van Amsterdam et al, 2004). However, it is known that patients with schizophrenia use cannabis relatively frequently, with a lifetime prevalence 97% and last-year prevalence 49% (Moore et al, 2012).…”

A comprehensive review of auditory verbal hallucinations: lifetime prevalence, correlates and mechanisms in healthy and clinical individuals

“…The subjective effects of substances such as cannabis are subject to individual variability which may be accounted for by biologically meaningful phenotypes such as schizotypy (e.g., Stirling et al, 2008). Even considering the well-documented relationship between cannabis and psychosis, cannabis is considered a component cause which operates against a background of other risk factors (Castle, 2013). Hallucinations experienced in these states can be acute and transitory, passing once the substance ceases activation in the body, or they can be more chronic and ingrained-possibly leading to the development of later psychoses (Barkus and Murray, 2010).…”

Latent Psychotic Symptom Profiles Amongst People Who Use Methamphetamine: What Do They Tell Us About Existing Diagnostic Categories?

“…There was also a high rate of polysubstance use, including cannabis use, in this sample. Cannabis use in particular has been related to increased risk of developing a psychotic disorder ( 39 , 40 ), and more cannabis frequent use is associated with an elevated occurrence of psychotic symptoms amongst people who use methamphetamine ( 23 ). However, we did not find any evidence of greater polysubstance use, including cannabis use, amongst participants who had a high probability of psychosis in this sample.…”