Patients with early psychosis who had never used cannabis showed worse smooth pursuit eye movement performance than patients whose psychosis developed in the context of cannabis use.
Psychiatrists, neuroscience researchers, psychosis treatment specialists
Large effect size (g=0.76-0.86) showing worse eye movement control in psychosis patients without cannabis history
What the researchers found
Among 91 participants across four groups, early psychosis patients without cannabis history had significantly worse smooth pursuit velocity gain compared to those with cannabis history (effect size g=0.76-0.86), suggesting less severe neurobiological alterations in cannabis-associated psychosis.
Why it matters
If psychosis that develops with cannabis use involves less severe underlying brain abnormalities than psychosis without cannabis, it could have implications for prognosis and treatment approaches.
The numbers in context
91 participants (28 psychosis+cannabis, 25 psychosis no cannabis, 16 controls+cannabis, 22 controls no cannabis); smooth pursuit impairment effect size g=0.76-0.86 between psychosis groups; significant patient x cannabis interaction (p=0.04).
How the study worked
Case-control study comparing four groups (psychosis with/without cannabis history, controls with/without cannabis) on smooth pursuit eye movements at three frequencies and antisaccade performance.
What this study cannot tell us
Small sample sizes in each group; cross-sectional design; cannabis use history was self-reported; medication effects could influence eye movements.
How to read the evidence
Small case-control study with novel neurobiological measures, limited by sample size and cross-sectional design.
When this study was published
Published in 2021.
The bigger picture
These findings align with the theory that cannabis-associated psychosis may represent a less neurobiologically impaired subtype, where the substance itself contributes substantially to pushing someone over the psychosis threshold.
Questions still open
- Do patients with cannabis-associated psychosis have better long-term outcomes if they stop using? Could eye movement testing help distinguish psychosis subtypes?
Common questions
What do eye movements reveal about psychosis?
Does this mean cannabis-caused psychosis is less severe?
Read the original research
Eye movements in patients in early psychosis with and without a history of cannabis use.
NPJ schizophrenia, 7(1), 24
Citation
Sami, Musa Basseer; Annibale, Luciano; O'Neill, Aisling; Collier, Tracy; Onyejiaka, Chidimma; Eranti, Savitha; Das, Debasis; Kelbrick, Marlene; McGuire, Philip; Williams, Steve C R; Rana, Anas; Ettinger, Ulrich; Bhattacharyya, Sagnik. (2021). Eye movements in patients in early psychosis with and without a history of cannabis use.. NPJ schizophrenia, 7(1), 24. https://doi.org/10.1038/s41537-021-00155-2
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