Among 341 first-episode psychosis patients, cannabis use was associated with nearly double the risk of converting to schizophrenia spectrum disorders compared to other substances.
Psychiatrists, early psychosis intervention teams, and addiction medicine specialists.
HR 1.96for conversion to schizophrenia with cannabis use vs. other substances in first-episode psychosis
What the researchers found
Cannabis use (versus other substances or polysubstance use) was associated with a higher risk of conversion to schizophrenia spectrum disorders (HR 1.96, p=0.001), with 86.9% of conversions occurring within the first five years.
Why it matters
Identifying which first-episode psychosis patients are most likely to develop schizophrenia allows for targeted early intervention, and cannabis appears to be a significant modifiable risk factor.
The numbers in context
341 patients (64.8% male, mean age 33.8). Cannabis was most commonly used substance (78.9%). 52.8% converted to schizophrenia/SSD. 86.9% of conversions within 5 years. Cannabis HR 1.96 (p=0.001).
How the study worked
Retrospective cohort study using hospital discharge records from Basurto University Hospital (2002-2016). Kaplan-Meier survival curves and Cox regression for conversion analysis.
Who was studied
341 patients discharged with first-episode psychosis from a Spanish university hospital (2002-2016).
What this study cannot tell us
Retrospective design. Single hospital. Cannot distinguish causation from association. Substance-induced psychosis and other FEP diagnoses had similar conversion rates, complicating interpretation.
How to read the evidence
Retrospective cohort with 15 years of data; provides useful risk estimates but subject to unmeasured confounding.
When this study was published
Covers 15 years of hospital data (2002-2016).
The bigger picture
This study adds to the evidence that cannabis is a particularly strong risk factor for progression from first psychosis to schizophrenia, regardless of whether the initial episode appeared substance-induced.
Replication
Single-center retrospective study; multi-center prospective studies would strengthen findings.
Funding
Not specified in abstract
Conflicts of interest
Not specified in abstract
Questions still open
- Would cannabis cessation after first psychosis reduce conversion rates?
- Are there genetic markers that identify which cannabis users are most vulnerable to conversion?
Read the original research
The transition to Schizophrenia spectrum disorder from a first psychotic episode that did or did not appear to be induced by substance use.
Psychiatry research, 328, 115475
Citation
Inchausti, Lucía; Gorostiza, Inigo; Gonzalez Torres, Miguel Angel; Oraa, Rodrigo. (2023). The transition to Schizophrenia spectrum disorder from a first psychotic episode that did or did not appear to be induced by substance use.. Psychiatry research, 328, 115475. https://doi.org/10.1016/j.psychres.2023.115475