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

The takeaway

A meta-analysis of six case-control studies found marijuana use was associated with a 34% lower risk of oral cancer, though the authors urge caution given methodological limitations.

Oncologists, oral health professionals, and epidemiologists studying cannabis-cancer relationships.

Marijuana use was associated with 34% lower oral cancer risk across 6 case-control studies

What the researchers found

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.

Why it matters

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.

The numbers in context

6 studies, 4,686 cases, 10,370 controls. Pooled OR=0.659 (95% CI: 0.500-0.869, p=0.003). I2=47.35% (moderate heterogeneity). Sensitivity ORs ranged from 0.599 to 0.708. Egger test p=0.532 (no publication bias detected).

How the study worked

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.

What this study cannot tell us

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.

How to read the evidence

Meta-analysis methodology is strong, but underlying studies are all case-control with heterogeneous exposure assessment. The inverse association is unexpected and requires prospective confirmation.

When this study was published

2025 publication with literature search through August 2025.

The bigger picture

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.

Questions still open

Is the apparent protective effect due to cannabinoid anti-tumor properties, or methodological artifacts in case-control designs?
Would prospective cohort studies confirm this inverse association?

Read the original research

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

Journal of ethnicity in substance abuse, 1-19

View on PubMed ↗Publisher’s paper ↗

Citation

Ibrahim Mohammad, Suleiman; Vasudevan, Asokan; Jawad, Mahmood; Sapaev, I B; Khudhair Abbas Al-Khafaji, Zahraa; Prasad, Kdv; Fakri Mustafa, Yasser; Abdulrazzaq Gati, Mohannad; Ali Ahmed, Batool; Ebrahimi, Amirali. (2025). The association between marijuana use and oral cancer risk: a systematic review and meta-analysis of case-control studies.. Journal of ethnicity in substance abuse, 1-19. https://doi.org/10.1080/15332640.2025.2581692