First Major Study Links Cannabis Use Disorder to Deadly Cancers : ScienceAlert

For the first time ever, more Americans are regularly using cannabis than they are drinking alcohol.

While smoking weed for a recreational high is considered by many to be a safer alternative to using tobacco or even drinking alcohol, there is a lack of evidence on the long-term health impacts of the drug. What little is known suggests it may not be as harmless as some think.

A new investigation from the American Head and Neck Society finds that excessive cannabis use disorder may increase the risk of developing any head or neck cancer, including oral, oropharyngeal, nasopharyngeal, salivary gland, and laryngeal cancer.

The study’s authors, led by epidemiologist Tyler Gallagher from the University of Southern California, Los Angeles, say their results should be “interpreted cautiously”, as there is a chance they did not fully control for alcohol and tobacco use, as well as HPV status – all of which can contribute to the risk of developing head or neck cancers.

What’s more, the study did not measure the amount or the potency of the cannabis participants consumed, how often it was consumed, or how the cannabis was consumed (whether it be vaped, smoked, or ingested).

Nevertheless, head and neck surgeon Niels Kokot from the University of Southern California says, “This is one of the first studies – and the largest that we know of to date – to associate head and neck cancer with cannabis use. The detection of this risk factor is important because head and neck cancer may be preventable once people know which behaviors increase their risk.”

The research relied on 20 years of clinical records belonging to 116,076 individuals diagnosed with a cannabis-related disorder that was “substantial enough to cause physical or emotional symptoms with the inability to cease cannabis use.”

This group was then compared to a cohort of nearly 4 million individuals who did not have cannabis use disorder.

In the end, the relative risk of developing head and neck cancer was 3.5 to 5 times greater for those with cannabis use disorder than those without.

To put that in perspective, the relative risk of developing a head and neck cancer for people who use tobacco is 2 to 10 times greater than those who don’t, while the relative risk for people who consume alcohol is 5.7 for oral and pharyngeal cancers, and 3.2 for laryngeal cancer.

“Given that our cohort included those with the highest use of cannabis, we can estimate that the association of cannabis use seen in this study with risk of developing HNC was slightly less than that of alcohol and tobacco use,” conclude Gallagher and his colleagues.

The results are intriguing, but more research is needed to figure out whether this association is causal and what mechanisms might be at play. The current cohort was assumed to be heavy cannabis users because of their diagnosis of cannabis use disorder, but their actual usage was never properly measured.

Previous clinical studies that have investigated the association between cannabis use and head and neck cancer have produced mixed results, and most did not find an association even after following cannabis users for up to eight years.

Earlier this year, the US Drug Enforcement Agency announced its plans to ease federal restrictions on cannabis, reclassifying it from a Schedule I drug to the less restricted Schedule III.

Scientists hope this action removes some of the current barriers to cannabis research, opening up the field like never before.

The study was published in JAMA Otolaryngology – Head & Neck Surgery.