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

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.

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.

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.

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.

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.