Objective: Cerebral gray matter volume reductions have been found to progress over time in schizophrenia, with larger decreases related to poorer outcome, which has also been associated with cannabis use in schizophrenia patients. Progressive gray matter changes in patients who use cannabis may be more extensive than in those who do not.
Method: Patients with recent-onset schizophrenia (N=51) and matched healthy subjects (N=31) were included. For all subjects, magnetic resonance imaging scans were obtained at inclusion (T0) and at 5-year follow-up (T5). Nineteen patients used cannabis but no other illicit drugs; 32 patients did not use any drugs during the 5-year follow-up. At T5, clinical outcome was measured. Cumulative amount of antipsychotic medication during the interval was calculated. At T0 and T5, total brain, gray and white matter, and lateral and third ventricle volumes were measured. Univariate analysis of covariance and pairwise comparisons were performed.
Result: Schizophrenia patients showed a larger gray matter volume decrease over time than healthy subjects. They also showed larger increases in lateral and third ventricle volumes than healthy subjects and patients who did not use cannabis during follow-up. This decrement was significantly more pronounced in the patients who continued to use cannabis. These differences could not be attributed to outcome or baseline characteristics.
Conclusions: First-episode schizophrenia patients who use cannabis show a more pronounced brain volume reduction over a 5-year follow-up than patients with schizophrenia who do not use cannabis. These results may help explain some of the detrimental effects of cannabis use in schizophrenia.