People who are regular and heavy cannabis users have a three to five times greater risk of developing some head and neck cancers, according to recent research, which adds to a growing pool of evidence that’s just beginning to explore the link between weed and cancer risk.
“The cannabinoids themselves could be carcinogenic, and it could also be that the smoke itself has potential for carcinogenesis,” said lead study author Dr Niels Kokot, a head and neck surgeon at Keck Medicine of the University of Southern California.
NBC News reports that Kokot and his team used data spanning two decades from a global database called TriNetX, which included patient information from 64 health centres throughout the America. Of the more than 4m people included, about 116 000 had been diagnosed with cannabis use disorder from April 2004 to April 2024.
The diagnoses were based on self-reported use of the drug – the patient having to tell a healthcare provider how often they used cannabis and how it affected them.
The researchers compared people with cannabis use disorder with those of a similar age and sex in the study without the disorder. Most of the people with cannabis use disorder in the study were white. None had a history of head and neck cancer before the study began.
The cannabis users in the study were more likely to develop all types of head and neck cancer except hypopharyngeal cancer, a type of lower throat cancer, compared with non-users. The most common types of head and neck cancer in both groups were oral cancers and cancer of the larynx.
The study authors noted several limitations that could skew the study’s findings. The first was that it’s very difficult to measure how many people regularly use cannabis when relying on self-reported data.
To be in this group, people would have had to tell a healthcare provider during a visit that they used cannabis very frequently – the equivalent of smoking about a joint per day, said Dr Joseph Califano, director of the Gleiberman Head and Neck Cancer Centre at the Moores Cancer Centre at the University of California-San Diego, who was not involved with the research.
The same is true for alcohol and tobacco use.
“The tough thing about this study and almost every study that looks at cannabis use is that we just don’t have the data,” said Califano, who wrote an editorial accompanying the new study, which was published in JAMA Otolaryngology-Head & Neck Surgery.
The study also looked at head and neck cancer diagnoses at two points in time: within the first year of being diagnosed with cannabis use disorder, and five years or beyond the diagnosis. It excluded, however, cancers found one to four years after a cannabis use disorder diagnosis.
This secondary analysis was used to determine how strong the association was: if it remained after five years, it’s more likely the association was strong.
They found that after five or more years, the cannabis use disorder group still had higher overall rates of head and neck cancer, but there was no longer a significantly increased risk for some specific types, including oral, laryngeal and oropharyngeal cancer.
“You would expect that over time, there would be an accumulative effect,” said Dr Glenn Hanna, a medical oncologist at the Dana-Farber Cancer Institute’s Centre for Head and Neck Oncology.
It’s still unclear what role dose, frequency and how a person ingests cannabis may affect their cancer risk. Califano noted that the new research links the increased risk to self-reported heavy users of cannabis, not occasional users.
Past studies that have investigated whether cannabis use increases a person’s risk for head and neck cancer have yielded mixed results. This newer study highlights the need for continued research on the subject, especially as daily marijuana use grows in popularity, Hanna said.
Despite the study’s limitations, “it still suggests there could be some association”, he said.
Cannabis and cancer risk
The cannabis plant contains more than 100 cannabinoids, including THC and CBD, and hundreds of non-cannabinoid chemicals. Scientists are just beginning to understand the effect these compounds have on the human body, both good and bad.
“Cannabinoids are powerful drugs that exert their effects at concentrations found with recreational use. We know that because you get high,” Califano said, noting that it’s almost unheard of to find a truly pure form of a single cannabinoid, such as CBD.
Hanna said that smoking anything, including cannabis, activates inflammatory pathways that could be involved in cancer formation.
Cannabinoids could also become carcinogenic in the body.
“There are biological reasons why someone would hypothesise that cannabis smoke could be harmful, but we’re not sure what the degree of increased risk is, if there is one, with head and neck cancer,” he said, noting that it’s difficult to tease out other risk factors, such as alcohol and tobacco use.
About 20% of the people in the study with cannabis use disorder reported frequent tobacco and alcohol use, compared with about 2% in the group without cannabis use disorder.
Keeping this in mind, edible cannabis may be safer than smoking the plant, Hanna said, acknowledging some of his patients use medical marijuana for health conditions.
But Califano said there’s reason to suspect some cannabinoids themselves – rather than the smoke – might be behind the increased cancer risk, if future research establishes a clear connection.
“Cannabinoids have a lot of effects that drive immune response, and all these other things that are involved with either how cancer develops or how our bodies fight cancer,” he said. “So it’s not unreasonable to think about the cancer-associated effects of cannabis use to be independent of whether or not you ingest smoke or vape or bake them into your brownies.”
Hanna and Califano acknowledge that cannabis is likely to have both positive and negative effects on health. As research uncovers more about its impact on the body, it’s possible that different cannabinoids will be found to have different effects on cancer risk.
“Some of them may be associated with cancer development; some may actually inhibit cancer development,” Califano said.
Study details
Cannabis use and head and neck cancer
Tyler Gallagher, Ryan Chung, Matthew Lin, et al
Published in JAMA Otolaryngology-Head & Neck Surgery on 8 August 2024
Abstract
Importance
Cannabis is the most commonly used illicit substance worldwide. Whether cannabis use is associated with head and neck cancer (HNC) is unclear.
Objective
To assess the clinical association between cannabis use and HNC.
Design, Setting, and Participants
This large multicentre cohort study used clinical records from a database that included 20 years of data (through April 2024) from 64 health care organisations. A database was searched for medical records for US adults with and without cannabis-related disorder who had recorded outpatient hospital clinic visits and no prior history of HNC. Propensity score matching was performed for demographic characteristics, alcohol-related disorders, and tobacco use. Subsequently, relative risks (RRs) were calculated to explore risk of HNC, including HNC subsites. This analysis was repeated among those younger than 60 years and 60 or older.
Exposure
Cannabis-related disorder.
Main Outcomes and Measures
Diagnosis of HNC and any HNC subsite.
Results
The cannabis-related disorder cohort included 116 076 individuals (51 646 women [44.5%]) with a mean (SD) age of 46.4 (16.8) years. The non–cannabis-related disorder cohort included 3 985 286 individuals (2 173 684 women [54.5%]) with a mean (SD) age of 60.8 (20.6) years. The rate of new HNC diagnosis in all sites was higher in the cannabis-related disorder cohort. After matching (n = 115 865 per group), patients with cannabis-related disorder had a higher risk of any HNC (RR, 3.49; 95% CI, 2.78-4.39) than those without HNC. A site-specific analysis yielded that those with cannabis-related disorder had a higher risk of oral (RR, 2.51; 95% CI, 1.81-3.47), oropharyngeal (RR, 4.90; 95% CI, 2.99-8.02), and laryngeal (RR, 8.39; 95% CI, 4.72-14.90) cancer. Results were consistent when stratifying by older and younger age group.
Conclusions and Relevance
This cohort study highlights an association between cannabis-related disorder and the development of HNC in adult patients. Given the limitations of the database, future research should examine the mechanism of this association and analyse dose response with strong controls to further support evidence of cannabis use as a risk factor for HNCs.
JAMA article – Cannabis Use and Head and Neck Cancer (Open access)
JAMA accompanying article – Cannabis and Head and Neck Cancer—Déjà Vu All Over Again? (Open access)
See more from MedicalBrief archives:
Cannabis for cancer-related symptoms – an unfulfilled promise?
More American adults now smoke cannabis than cigarettes
Is marijuana as safe as we think?
Physicians search for medicinal cannabis knowledge – Australia and SA