New research links heavy, problematic cannabis use to a worrying rise in oral cancer cases, raising urgent questions about the health impacts of legalization.
Study: Cannabis use disorder and five-year risk of oral cancer in a multicenter clinical cohort. Image credit: Tayler Derden/Shutterstock.com
As more American states legalize cannabis use, cannabis disorder (CUD) is becoming more common. Yet little is known about how it affects long-term health. A recent study in Preventive Medicine Reports examines the associations of CUD with risk of oral cancer (specifically malignant neoplasms of the lip or tongue) over five years from the first drug use disorder screening.
Introduction
Cannabis and tobacco have several cancer-causing chemicals in common. Burning cannabis produces polycyclic aromatic hydrocarbons, benzo[a]pyrene, and phenols, like tobacco combustion. Tobacco is well-known to cause cancers in the oral cavity, prompting the current exploration into similar risks with cannabis.
Prior research did not provide conclusive or concordant results, though there is a suggestion of a higher risk for head and neck cancer among frequent cannabis users. Differences in methods, inadequate follow-up, and poorly controlled confounding factors may account for this.
CUD refers to the problematic use of cannabis and is linked to frequent cannabis exposure. However, many people who overuse cannabis do not fit the CUD definition.
Earlier research indicates that people who smoke 14 or more cannabis joints a week are more likely than not to have CUD. The current study did not use this as a diagnostic criterion but noted it as a reference point from earlier work; in this study, CUD was defined based on new ICD-coded diagnoses in clinical records.
The researchers examined electronic health records from a large University of California Health Data Warehouse database. These records come from six teaching clinics or hospitals.
Study findings
The study included 45,129 patients who completed drug use disorder screening and had no prior oral cancer diagnosis. Of these, 949 (2.1%) developed CUD during the five-year follow-up period. The mean age of the whole cohort was 45 years, with 54% female. About 6% were smokers.
A total of 106 patients developed oral cancer during follow-up. The percentage was tripled in the CUD group compared to others. That is, 0.74% of CUD patients developed oral cancer vs 0.23% in the others. The latter agrees with the population-level risk estimated by other studies.
After adjusting for confounding factors, including body mass index (BMI) as a continuous variable, smoking, age, and sex, the odds of oral cancer were more than tripled in the CUD group, and the risk was similarly threefold increased in this group compared to non-CUD patients.
Older age was associated with a 4% higher risk per additional year of age, while females and those with higher body weight had a 3-6% decreased risk.
Smoking was the only factor that did not show an association with increased oral cancer risk, possibly because so few of the cohort were smokers. When smokers with CUD were compared to smokers without CUD, the former had a six-fold risk of oral cancer after controlling for other factors.
Importantly, the risk of oral cancer in this cohort was still low, but the threefold increase in risk with CUD over just five years is a disturbing observation. It fits with the known ability of cannabis smoke to damage respiratory tract cells, like tobacco. Such changes include dysplastic and metaplastic changes independent of accompanying tobacco use.
Cell studies have shown that cannabis contains chemicals capable of damaging DNA and causing chromosomal abnormalities. Preclinical studies also indicated precancerous and cancerous changes in lung tissue following the inhalation of cannabis smoke.
Cannabis also suppresses both innate and adaptive immune responses, primarily because of Δ9-tetrahydrocannabinol. This could help tumors get a head start as immune surveillance is disrupted, especially in the oral and lung tissues that are directly exposed to cannabis smoke.
Finally, people with CUD may also drink alcohol, smoke tobacco, and have other overlapping behavioral and social risk factors associated with the risk of oral cancer.
Conclusions
The findings of this study show a threefold risk of oral cancer in the first five years after the first diagnosis of CUD.
This emphasizes the need to screen for oral cancers in all patients who abuse or overuse addictive substances, or who come in for counseling, as many may not even consider their cannabis use to be abnormal or a matter of concern. The findings of this study challenge the popular perception that cannabis is a safe substance and the growing legalization of recreational cannabis use.
Future studies should investigate correlations between oral cancer and the frequency, duration, or cumulative exposure. More follow-up research is required to capture the health outcomes of recreational cannabis use and CUD, whether smoked or ingested, to develop health policies based on solid evidence and not popular demand.
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