NBC News
A study published this Thursday in the journal JAMA Otolaryngology-Head & Neck Surgery suggests that regular marijuana use may increase the risk of developing some types of head and neck cancer.
The research concluded that cannabis users were 3.5 to 5 times more likely to develop these types of cancers than those who did not use the drug regularly.
Head and neck cancers are cancers of the mouth, throat and nasal cavity and are twice as common in men as in women, according to the Centers for Disease Control and Prevention.
This new research adds to a somewhat confusing body of evidence that is only just beginning to explore the impact cannabis may have on cancer risk.
“Cannabinoids themselves may be carcinogenic, and it may also be that smoke itself has carcinogenic potential,” says study senior author Niels Kokot, a head and neck surgeon at Keck Medicine of the University of Southern California.
Kokot and his team used 20 years of data from a global database called TriNetX, which included patient information from 64 health centers across the United States. Of the more than four million people included, about 116,000 had been diagnosed with cannabis use disorder between April 2004 and April 2024. The diagnoses were based on cannabis use — in other words, the patient told a health care professional how often they used cannabis and how it affected them.
Researchers compared people with cannabis use disorder to age- and sex-matched people in the study without cannabis use disorder. Most people with cannabis use disorder in the study were white. None had a history of head and neck cancer before starting the study.
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 and laryngeal.
The study’s authors noted that there were several limitations that could bias their conclusions. The first is that it is very difficult to measure how many people regularly use cannabis when relying on self-reported data.
To be in this group, people had to have told a health care professional at a visit that they used cannabis very frequently, the equivalent of smoking about a joint a day, said Joseph Califano, director of the Gleiberman Head and Neck Cancer Center at the University of California San Diego Moores Cancer Center, who was not involved in the study.
The same is true for alcohol and tobacco consumption.
“The difficult thing about this study and almost all studies looking at cannabis use is that we don’t have the data,” said Califano, who wrote an editorial that accompanied the new study.
The study also looked at head and neck cancer diagnoses at two time points: within the first year after cannabis use disorder diagnosis and five years or more after diagnosis. Cancers detected between one and four years after cannabis use disorder diagnosis were excluded, however. This secondary analysis was used to determine the strength of the association: If it remained after five years, the association was more likely to be 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 of some specific types, such as oral, laryngeal and oropharyngeal cancer.
“You would expect there to be a cumulative effect over time,” said Glenn Hanna, a medical oncologist at the Head and Neck Cancer Center at Dana-Farber Cancer Institute.
It’s not yet clear what role the dose, frequency and way a person ingests cannabis may play in their cancer risk,” Califano said. The new research links the increased risk to regular cannabis users, not occasional ones.
Previous studies investigating whether cannabis use increases the risk of head and neck cancer have yielded mixed results. The new study underscores the need for further research on the topic, especially as daily marijuana use grows in popularity, Hanna said.
Despite the study’s limitations, “it still suggests there may be some association,” he said.
Cannabis and cancer risk
The cannabis plant contains over 100 cannabinoids, including THC and CBD, and hundreds of non-cannabinoid chemicals. Scientists are only just beginning to understand the effect these compounds have on the human body, both good and bad.
“Cannabinoids are potent drugs that exert their effects in concentrations found in recreational use. We know this because it affects you,” Califano said, noting that it is 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 might hypothesize that cannabis smoke might be harmful, but we’re not sure what the degree of increased risk is, if any, with head and neck cancer,” she said, noting that it’s difficult to separate out other risk factors, such as alcohol and tobacco use. About 20% of 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.
With that in mind, edible cannabis may be safer than smoking the plant, Hanna said, acknowledging that some of his patients use medical marijuana for health problems.
But Califano said there is reason to suspect that some cannabinoids themselves — rather than smoke — could 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 in how cancer develops or how our bodies fight it,” she added. “So it’s not unreasonable to think that the cancer-associated effects of cannabis use would be independent of whether or not you smoke it or vape it or bake it into brownies.”
Hanna and Califano acknowledge that cannabis is likely to have both positive and negative health effects. As research uncovers more about cannabis’ impact on the body, different cannabinoids are likely to be found to have different effects on cancer risk.
“Some of them may be associated with the development of cancer, while others may inhibit it,” Califano said.
