The association between marijuana use and oral cancer risk: a systematic review and meta-analysis of case-control studies

The relationship between marijuana use and oral cancer risk remains controversial, with conflicting evidence from epidemiological studies. This systematic review and meta-analysis aimed to synthesize available evidence on the association between marijuana consumption and oral cancer incidence. Following PRISMA guidelines, we conducted comprehensive searches across Scopus, PubMed, Web of Science, and Embase databases up to August 2025. We included only case-control studies reporting quantitative risk estimates for marijuana use and histologically confirmed oral cancer (ICD-10 codes C00-C06). Data extraction followed standardized protocols, and study quality was assessed using the Joanna Briggs Institute checklist. Statistical analyses were performed using Comprehensive Meta-Analysis software with random-effects models. Heterogeneity was evaluated using I² statistics, and publication bias was assessed through funnel plots and Egger's regression test. Six case-control studies involving 4,686 cases and 10,370 controls were included. The pooled odds ratio demonstrated a statistically significant inverse association between marijuana use and oral cancer risk (OR = 0.659, 95% CI: 0.500-0.869, <i>p</i> = 0.003, I² = 47.35). Subgroup analyses were performed based on the duration of use, gender, and age at initiation of marijuana use; however, no clear dose-response relationship was observed. Sensitivity analyses confirmed robustness of findings, with ORs ranging from 0.599 to 0.708 across iterations. No significant publication bias was detected (Egger's test <i>p</i> = 0.532). Three individual studies showed statistically significant protective effects, while three others were non-significant. This meta-analysis suggests marijuana use is associated with reduced oral cancer risk. However, given methodological limitations, heterogeneity in exposure assessment, and conflicting recent evidence, these findings require cautious interpretation. Future large-scale prospective cohort studies with standardized exposure measurements are essential for definitive conclusions.