Among 247 first-episode psychosis patients, daily marijuana use in the 5 years before onset doubled the rate of developing psychosis, independent of alcohol and tobacco use, with escalation of use being the strongest predictor.
Read this if you want to understand the timing relationship between marijuana use and the development of psychotic disorders.
Going from no use to daily use tripled the rate of psychosis onset (HR = 3.6)
What the researchers found
This study examined 247 people experiencing their first episode of psychosis to determine whether marijuana use in the preceding years was temporally linked to psychosis onset.
Escalation of marijuana use in the 5 years before psychosis onset was highly predictive. Going from no use to daily use during this period increased the hazard of psychosis onset by 3.6 times. Daily use at any point approximately doubled the rate of onset (HR = 2.2), even after controlling for alcohol and tobacco use.
Cumulative marijuana exposure was independently associated with an increased rate of psychosis onset, regardless of gender or family history. Importantly, the strength of the association was similar before and after the onset of prodromal symptoms, suggesting that escalating use is not simply a response to early psychotic experiences.
The study also found that early adult use (not just adolescent use) was associated with faster onset, challenging the focus exclusively on teen use.
Why it matters
This study provides some of the clearest temporal evidence linking marijuana escalation to psychosis onset. By demonstrating that the association exists both before and after prodromal symptom onset, and is independent of other substance use, it strengthens the case for a contributory role of marijuana in psychosis.
The numbers in context
Escalation from no use to daily use: HR = 3.6 (p<0.0005). Daily use: HR = 2.2 (p<0.0005). Cumulative exposure associated with onset (p = 0.007). Independent of gender, family history, and concurrent alcohol/tobacco use. 247 first-episode patients from 6 psychiatric units.
How the study worked
Enrolled 247 first-episode psychosis patients from six psychiatric units. Collected detailed lifetime marijuana, alcohol, and tobacco use histories and ages at onset of prodrome and psychosis in 210 patients. Cox regression (survival analysis) quantified hazard ratios for premorbid use variables.
What this study cannot tell us
Retrospective recall of substance use history may be inaccurate, especially during prodromal periods when cognitive function is declining. No control group of cannabis users who did not develop psychosis. Cannot definitively establish causation. Cannabis potency was not measured.
How to read the evidence
Longitudinal design with survival analysis and control for confounders, but retrospective substance use data and no non-psychosis control group.
When this study was published
Published in 2016. Cannabis potency has continued to increase, which may affect the strength of these associations.
The bigger picture
This study adds an important temporal dimension to the cannabis-psychosis debate. Rather than just showing that people with psychosis used more marijuana, it demonstrates that escalating use precedes and predicts the timing of psychosis onset, making a stronger case for a contributory relationship.
Questions still open
- Would reducing cannabis use during the premorbid period delay or prevent psychosis onset? Is there a threshold of cumulative exposure below which the risk is minimal? How does cannabis potency affect this relationship?
Common questions
Does marijuana use speed up the onset of schizophrenia?
Is only teenage marijuana use risky for psychosis?
Read the original research
Marijuana use in the immediate 5-year premorbid period is associated with increased risk of onset of schizophrenia and related psychotic disorders.
Schizophrenia research, 171(1-3), 62-7
Citation
Kelley, Mary E; Wan, Claire Ramsay; Broussard, Beth; Crisafio, Anthony; Cristofaro, Sarah; Johnson, Stephanie; Reed, Thomas A; Amar, Patrick; Kaslow, Nadine J; Walker, Elaine F; Compton, Michael T. (2016). Marijuana use in the immediate 5-year premorbid period is associated with increased risk of onset of schizophrenia and related psychotic disorders.. Schizophrenia research, 171(1-3), 62-7. https://doi.org/10.1016/j.schres.2016.01.015
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