Cannabis use is a known risk factor for psychosis. Among three inpatient groups—cannabis-induced psychosis, schizophrenia with cannabis use, and schizophrenia without cannabis use—those with cannabis-induced psychosis had lower negative symptom scores, fewer auditory hallucinations, and more mania than those with schizophrenia and cannabis use. Few clinical differences appeared between schizophrenia groups regardless of cannabis history. The age of first admission for psychosis was lower in both cannabis-using groups, suggesting cannabis precipitates psychotic symptoms.
Among patients hospitalized for a psychotic episode, those whose psychosis was triggered by substances were more likely to have a personal history of personality disorder, family history of addictions, and more positive symptoms, while those with non-substance-induced psychosis had greater illness severity, more negative symptoms, and more family history of psychosis. Over six years of follow-up, 40.9% of the substance-induced group later received a schizophrenia diagnosis; these individuals had more family history of psychotic disorders and worse outcomes, including more emergency visits and readmissions, compared with those whose diagnosis remained stable.