Impact of cannabis use and cannabis composition on formal thought disorder and related brain networks: An fMRI study in 51 patients with schizophrenia.

Bernabeu T.; Argote M.; Citterio-Quentin A.; Giloux N.; Sescousse G.; Rolland B. · Schizophrenia research · 2026

**Background & Methods** This fMRI study examined 51 patients with schizophrenia stratified by cannabis use status to investigate whether cannabis consumption is associated with altered functional connectivity between temporal gyri and striatal regions and increased formal thought disorder (FTD). The research employed region-of-interest (ROI)-to-ROI and seed-based connectivity analyses, correlation tests, and mediation models using both frequentist and Bayesian statistical approaches, with FTD measured via the conceptual disorganization item from the Positive And Negative Syndrome Scale. **Key Findings** • No significant differences in functional connectivity between cannabis users and non-users were identified in cortico-striatal brain networks previously associated with FTD in schizophrenia. • THC/CBD ratio was not significantly associated with either cortico-striatal connectivity or formal thought disorder severity, contradicting prior findings linking elevated THC/CBD ratios to increased FTD. • Bayesian analysis provided moderate to strong evidence supporting the null hypothesis across most statistical models, suggesting cannabis use may not account for FTD-related connectivity alterations previously reported in schizophrenia populations. **Dosage & Administration** Not reported. The study stratified participants by cannabis use status but did not specify frequency, quantity, potency, or administration route. **Safety & Adverse Effects** Not reported. The study focused on neurobiological connectivity outcomes and symptom severity rather than documenting adverse effects or safety profiles. **Evidence Quality** This study presents moderate evidence quality with several limitations. The small sample size (n=51) reduces statistical power and generalizability. The cross-sectional design prevents causal inference regarding cannabis use and brain connectivity. The authors acknowledge that cannabis composition assessment was limited and that dose-response relationships were not thoroughly examined. The lack of significant findings, while supported by Bayesian evidence favoring the null hypothesis, may reflect insufficient power to detect meaningful effects. The study is strengthened by multimodal statistical approaches (frequentist and Bayesian) and standardized symptom measurement, but larger prospective studies incorporating detailed cannabis composition analysis, dose quantification, temporal patterns of use, and comprehensive symptom dimensional assessment are needed to refine understanding of cannabis effects on cortico-striatal connectivity and formal thought disorder in schizophrenia.

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