For the first time in history, the number of Americans who regularly use marijuana outnumbers those who drink alcohol.
Smoking marijuana to get high recreationally is considered by many to be a safer alternative to tobacco and alcohol, but there is a lack of evidence about the drug’s long-term health effects. What little is known suggests that marijuana may not be as harmless as some think.
A new study from the American Head and Neck Society has found that cannabis excessive use disorder may increase the risk of developing all head and neck cancers, including oral cavity, oropharyngeal, nasopharyngeal, salivary gland and laryngeal cancers.
The study authors, led by epidemiologist Tyler Gallagher of the University of Southern California, Los Angeles, said their findings should be “interpreted with caution” because they may not have fully taken into account factors that may contribute to a person’s risk of developing head and neck cancer, such as alcohol and tobacco use and HPV status.
Additionally, the study did not measure the amount or potency of cannabis consumed by participants, how often they consumed it, or how they consumed it (vaping, smoking, or ingesting it).
Still, Niels Kokott, a head and neck surgeon at the University of Southern California, said, “This is one of the first studies to show an association between head and neck cancer and cannabis use, and the largest we know of to date. Detecting this risk factor is important because head and neck cancer may be preventable if people know what behaviors increase their risk.”
The study was based on 20 years of clinical records of 116,076 people diagnosed with cannabis-related disorders “severe enough to cause physical or mental symptoms that make it difficult to stop using cannabis.”
This group was then compared to a cohort of approximately 4 million people without cannabis use disorder.
Overall, people with cannabis use disorder had a 3.5 to 5 times higher relative risk of developing head and neck cancer than those without the disorder.
To put this in perspective, the relative risk of developing head and neck cancer for tobacco smokers is 2 to 10 times higher than for non-smokers, while the relative risk for alcohol users is 5.7 times higher for oral cavity and pharyngeal cancer and 3.2 times higher for laryngeal cancer.
“Given that our cohort included people who were among the heaviest cannabis users, we can estimate that the association between cannabis use and risk of developing HNC identified in this study is slightly weaker than the associations with alcohol and tobacco use,” Gallagher and his colleagues conclude.
Although the results are intriguing, further research is needed to determine whether this association is causal and what mechanisms may be at work. The current cohort was assumed to be heavy cannabis users because they had been diagnosed with cannabis use disorder, but their actual use had never been adequately measured.
Previous clinical studies looking at the link between cannabis use and head and neck cancer have had mixed results, with most finding no association even after following cannabis users for up to eight years.
Earlier this year, the U.S. Drug Enforcement Administration announced plans to loosen federal restrictions on cannabis, reclassifying it from a Schedule I drug to a less regulated Schedule III.
Scientists hope that this measure will remove some of the current barriers to cannabis research and allow the field to open up like never before.
The study was published in JAMA Otolaryngology – Head & Neck Surgery.
