Early cannabis use linked to drug-induced psychosis while later use linked to schizophrenia in homeless adults | Research

The takeaway

Among 437 homeless and precariously housed adults, those who first used cannabis before age 15 had higher odds of substance-induced psychosis, while those starting after 15 had higher odds of schizophrenia or schizoaffective disorder.

Psychosis researchers, homelessness health providers, adolescent brain development specialists

Early use: OR=1.09 for substance-induced psychosis; later use: OR=2.19 for schizophrenia

What the researchers found

Early cannabis exposure (by age 15) was associated with increased risk of substance-induced psychosis (OR=1.09, p<0.05). Later first use (after age 15) increased risk of schizophrenia or schizoaffective disorder (OR=2.19, p<0.01). No cognitive differences were found between groups, though brain imaging showed differences in the lateral orbitofrontal cortex and white matter tract diffusivity.

Why it matters

The differential association between timing of cannabis use and type of psychotic disorder suggests different developmental mechanisms. This has implications for understanding how cannabis affects the developing brain at different stages.

The numbers in context

437 subjects; early use (by 15) OR=1.09 for substance-induced psychosis (p<0.05); later use (after 15) OR=2.19 for schizophrenia/schizoaffective (p<0.01); brain differences in lateral orbitofrontal cortex and white matter diffusivity

How the study worked

Cross-sectional study of 437 homeless/precariously housed adults recruited from single-room occupancy hotels in Vancouver's Downtown Eastside. Psychiatric diagnoses determined clinically. Psychotic symptoms measured with 5-factor PANSS. Neurocognitive battery and structural/diffusion tensor MRI completed.

What this study cannot tell us

Cross-sectional design cannot establish causation. Retrospective recall of age of first use. Homeless/precariously housed population has many confounding risk factors (poverty, trauma, polysubstance use). Selection bias inherent in studying this population.

How to read the evidence

Moderate-sized study in a unique population with both clinical, cognitive, and neuroimaging data, though cross-sectional design and confounding factors limit causal conclusions.

When this study was published

Published in 2021.

The bigger picture

The finding that timing of first cannabis use predicts different psychotic outcomes challenges the idea of a single "cannabis-psychosis pathway" and suggests that the developing brain may be vulnerable to different types of psychotic disruption at different ages.

Questions still open

What neurobiological mechanisms differ between early and later cannabis exposure to produce different psychotic outcomes? Could the early-use group's substance-induced psychosis eventually progress to a primary psychotic disorder?

Common questions

Does it matter when someone starts using cannabis?

In this study, yes. Starting before age 15 was linked to drug-induced psychosis, while starting after 15 was linked to schizophrenia or schizoaffective disorder. The timing of first exposure appears to influence which type of psychotic condition develops.

Were there brain differences?

Yes. Brain imaging revealed differences in the lateral orbitofrontal cortex and white matter tract diffusivity between early and later cannabis users, suggesting the timing of exposure may affect different neurodevelopmental processes.

Read the original research

Differential effects of cannabis exposure during early versus later adolescence on the expression of psychosis in homeless and precariously housed adults.

Progress in neuro-psychopharmacology & biological psychiatry, 106, 110084

View on PubMed ↗Publisher’s paper ↗

Citation

Gicas, Kristina M; Cheng, Alex; Panenka, William J; Kim, David D; Yau, Jade C; Procyshyn, Ric M; Stubbs, Jacob L; Jones, Andrea A; Bains, Simran; Thornton, Allen E; Lang, Donna J; Vertinsky, Alexandra T; Rauscher, Alex; Honer, William G; Barr, Alasdair M. (2021). Differential effects of cannabis exposure during early versus later adolescence on the expression of psychosis in homeless and precariously housed adults.. Progress in neuro-psychopharmacology & biological psychiatry, 106, 110084. https://doi.org/10.1016/j.pnpbp.2020.110084