Abruptly stopping heavy, daily cannabis use can trigger psychosis, both in people experiencing their first episode and in those with a pre-existing psychotic disorder. A systematic review of 21 studies identified 44 individuals whose psychosis began after cannabis withdrawal, and a health-record search found another 68 cases. Almost all were daily users who stopped abruptly. Those who resumed cannabis after the acute psychotic episode were far more likely to relapse than those who abstained (odds ratio 13.9). The findings indicate that acute psychotic symptoms can emerge after cannabis cessation, not only during its use.
Cannabis use is associated with an increased risk of developing psychotic disorders among people already at clinical high risk for psychosis. In a prospective study of this population, cannabis use was linked to a higher incidence of psychotic disorders and to more persistent psychotic symptoms, as well as poorer functional outcomes. The findings strengthen evidence that cannabis acts as a risk factor for psychosis, though the direction of causality remains debated.