Cannabis use preceded psychosis onset in 94% of first-episode patients | Research

The takeaway

Among 246 first-episode psychosis patients, 78% had cannabis exposure and 94% of them began using cannabis years before either prodromal or full psychotic symptoms appeared.

Psychiatrists, early psychosis intervention teams, prevention researchers, and policymakers considering cannabis and mental health.

94% used cannabis before psychosis onset; 78% had exposure

What the researchers found

Cannabis exposure (78%) and cannabis use disorders (47%) were highly prevalent at first-episode admission. In 94% of participants, cannabis use preceded onset of both attenuated and full-threshold psychosis symptoms by several years. Earlier age at first cannabis exposure was associated with younger age at prodrome and psychosis onset, worse premorbid functioning, and greater CUD severity at admission.

Why it matters

The finding that cannabis use preceded psychosis in the vast majority of cases strengthens the temporal argument for a contributory role, though it does not prove causation. The dose-response with earlier exposure adds to the concern.

The numbers in context

246 first-episode patients. 78% had cannabis exposure. 47% had cannabis use disorders. 94% used cannabis before symptom onset. Earlier exposure linked to younger psychosis onset, worse premorbid functioning, and greater CUD severity.

How the study worked

Consecutive admissions (N=246) to two community-based first-episode psychosis services. Characterized timing of cannabis use relative to prodromal and psychotic symptom onset, compared exposed vs. unexposed groups, and examined associations with age at first cannabis exposure.

What this study cannot tell us

Retrospective design relying on patient recall of symptom and use onset timing. Cannot establish causation. Community-based sample may not represent all first-episode cases. No control group of cannabis users who did not develop psychosis.

How to read the evidence

Large consecutive first-episode sample with detailed temporal data, but retrospective and lacking a non-psychosis control group.

When this study was published

Published in 2022.

The bigger picture

As cannabis becomes more widely available and potent, documenting the prevalence and timing of use in first-episode psychosis populations takes on public health urgency for prevention strategies.

Questions still open

What proportion of cannabis users in the general population develop psychosis? Could screening cannabis users for prodromal symptoms enable earlier intervention?

Common questions

Does cannabis cause psychosis?

In 94% of first-episode psychosis patients who used cannabis, use began years before psychotic symptoms appeared. While this temporal pattern is consistent with a contributory role, it does not prove cannabis caused the psychosis.

Does the age someone starts using cannabis matter for psychosis risk?

Yes. Earlier age at first cannabis use was associated with younger age at psychosis onset, worse premorbid functioning, and more severe cannabis use disorder at admission.

Read the original research

Timing of cannabis exposure relative to prodrome and psychosis onset in a community-based first episode psychosis sample.

Journal of psychiatric research, 147, 248-253

View on PubMed ↗Publisher’s paper ↗

Citation

Kline, Emily R; Ferrara, Maria; Li, Fangyong; D'Souza, Deepak Cyril; Keshavan, Matcheri; Srihari, Vinod H. (2022). Timing of cannabis exposure relative to prodrome and psychosis onset in a community-based first episode psychosis sample.. Journal of psychiatric research, 147, 248-253. https://doi.org/10.1016/j.jpsychires.2022.01.039