New meta-analysis links cannabis use to reduced risk of oral cancer

A new meta-analysis conducted by researchers from Jordan, Iraq, and Uzbekistan suggests that the consumption of cannabis could be associated with a significant reduction in the risk of oral cancer.

Based on data from more than 15,000 participants, the study adds an unexpected detail about the health effects of the plant, while urging caution in interpreting the results.

A study involving more than 15,000 participants

The research team examined six case-control studies, covering 4,686 patients diagnosed with oral cancer and 10,370 witnesses without the disease. All of the selected studies, conducted before August 2025, included cases histologically confirmed and quantitative assessments of cannabis exposure.

«In accordance with the PRISMA guidelines, we conducted comprehensive searches of the Scopus, PubMed, Web of Science, and Embase databases through August 2025. We included only case-control studies reporting quantitative estimates of the risk associated with cannabis use and histologically confirmed oral cancer,» the authors explained.

By compiling the available data, the researchers observed a inverse association between cannabis use and the incidence of oral cancer. The combined results revealed a odds of 0.659, which corresponds to a estimated 34 % reduction in risk for consumers compared to non-consumers.

The authors described this figure as «statistically significant,» meaning that it exceeds what would generally be attributed to chance.

A protective effect with no dose-response relationship

A central question in epidemiology is whether a greater consumption or consumption over a longer period has a stronger effect. In this case, the researchers found that no dose-response relationship, which means that some consumption levels Higher levels were not associated with greater protective effects.

«Subgroup analyses were conducted based on duration of use, sex, and age at the onset of marijuana use; however, no clear dose-response relationship was observed,» the study states.

This lack of correlation complicates the interpretation. In many areas of medical research, a dose-response relationship supports causal hypotheses. Here, its absence raises questions about potential confounding factors, such as lifestyle-related variables or misclassification of cannabis exposure.

Nevertheless, the sensitivity analyses conducted by the authors showed that the overall result remained stable even when certain individual studies were excluded. The odds ratios across the different iterations of the model ranged from 0.599 to 0.708, indicating a robustness despite the heterogeneity of the data.

A growing number of studies

This study This comes as the medical literature continues to explore the role of the cannabis in symptom management and its potential therapeutic effects. The authors noted that a recent study conducted in Thailand found longer survival among patients with aggressive cancers who used cannabis during palliative care. However, the mechanisms underlying any protective association—if it exists—remain unknown.

Three of the six studies included in the analysis showed statistically significant protective effects, while the other three did not. According to the researchers, this discrepancy reflects the broader scientific debate.

The team also evaluated the publication bias, without finding any significant bias that might artificially inflate the positive results.

However, despite this promising association, the authors repeatedly emphasized the need for caution. «This meta-analysis suggests that marijuana use is associated with a reduced risk of oral cancer. However, given the methodological limitations, the heterogeneity in exposure assessment, and recent conflicting evidence, these results should be interpreted with caution,» the article states.