Meta-Analysis Finds Cannabis Use Associated with Lower Oral Cancer Risk

Pooling six case-control studies (4,686 cases, 10,370 controls), marijuana use was associated with significantly lower oral cancer risk (OR=0.659, 95% CI: 0.500-0.869, p=0.003). Sensitivity analyses confirmed robustness (ORs 0.599-0.708). No clear dose-response relationship was observed. Three individual studies showed significant protective effects while three were non-significant.

Systematic review and meta-analysis following PRISMA guidelines. Searched Scopus, PubMed, Web of Science, and Embase through August 2025. Included only case-control studies with histologically confirmed oral cancer. Random-effects model with heterogeneity and publication bias assessment.

Given that cannabis smoke contains many of the same carcinogens as tobacco smoke, a protective association with oral cancer is counterintuitive and demands further investigation into potential anti-tumor mechanisms.

While preclinical studies have shown cannabinoids can kill cancer cells, the epidemiological evidence for cancer risk with cannabis use has been mixed. This meta-analysis adds to a pattern of null or protective associations for head and neck cancers, contrasting with the clear carcinogenic effects of tobacco.

All included studies were case-control (not cohort), which is more prone to recall and selection bias. Only six studies met inclusion criteria. Heterogeneity in how marijuana exposure was measured across studies. No dose-response relationship found. The authors themselves urge cautious interpretation.