A study released Thursday in JAMA Otolaryngology-Head & Neck Surgery found that heavy pot use regularly may raise the risk of some types of head and neck cancer.
The study found that people who used cannabis a lot were 3.5 to 5 times more likely to get head and neck cancers than people who didn’t use cannabis often.
Head and neck cancers affect the mouth, throat, and nose. The Centers for Disease Control and Prevention say that men are twice as likely as women to get these types of cancer.
The study adds to a body of mixed data that is only just starting to look into how cannabis may affect the risk of getting cancer.
“The cannabinoids could cause cancer, and it’s also possible that the smoke itself could cause cancer,” said Dr. Niels Kokot, head and neck surgeon at Keck Medicine of the University of Southern California and lead author of the study.
Kokot and his group used information from 64 health centers across the US that was stored in a global database called TriNetX. The data covered 20 years and had information on patients. Between April 2004 and April 2024, about 116,000 of the more than 4 million people in the study had been identified with a cannabis use disorder. The findings were based on how often the patients said they used cannabis and how it made them feel.
They looked at people with cannabis use disorder and people of the same age and gender who did not have cannabis use disorder. Most of the people in the study who had a cannabis use problem were white. Before the study started, none of them had ever had head and neck cancer.
The people who used cannabis were more likely than those who didn’t use cannabis to get all types of head and neck cancer except hypopharyngeal cancer, which is a type of lower throat cancer. Cancer of the mouth and throat was the most common type of head and neck cancer in both groups.
The people who wrote the study said some problems could make the results less accurate. Regarding the first point, it’s tough to figure out how many people use weed if they only report it themselves.
According to Dr. Joseph Califano, director of the Gleiberman Head and Neck Cancer Center at the Moores Cancer Center at the University of California, San Diego, people would have had to tell their doctor during a visit that they used cannabis very often, which is about a joint a day. This person would then be put into this group.
The same is true for smoking and drinking.
“We just don’t have the data for this study and almost every other study that looks at cannabis use,” Califano said in an opinion that came out at the same time as the new study.
The study also looked at people who were identified with head and neck cancer at two different times: within the first year of being diagnosed with cannabis use disorder and five years or more after the diagnosis. But cancers found one to four years after a cannabis use disorder diagnosis were left out. This secondary study was used to find out how strong the link was: if it was still there after five years, it meant the link was probably strong.
The cannabis use disorder group still had a higher general risk of head and neck cancer after five years or more, but there was no longer a significantly higher risk for some types, such as oral, laryngeal, and oropharyngeal cancer.
An oncologist at the Dana-Farber Cancer Institute’s Center for Head and Neck Oncology named Dr. Glenn Hanna said, “Over time, you would expect that there would be an accumulative effect.”
It’s still not clear how the amount, frequency, and way that a person smokes weed may affect their risk of getting cancer. Califano said that the new study shows that the higher risk is only for people who say they use cannabis a lot, not for people who only use it sometimes.
There have been mixed results from past studies that tried to find out if using cannabis raises the chance of getting head and neck cancer. Hanna said that the new study shows that more research needs to be done on the topic, especially since more and more people are using weed every day.
Even though the study had some flaws, he said, “it still suggests there could be some association.”
Cannabis and the risk of cancer
There are more than 100 cannabinoids in the cannabis plant, such as THC and CBD, and hundreds of chemicals that are not cannabinoids. They are just now starting to figure out what effects these chemicals have on the body, both good and bad.
“Cannabinoids are strong drugs that work best at the levels used for recreational purposes.” “That’s because you get high,” Califano said, adding that it’s very rare to find a form of a single cannabis that is 100% pure.
Hanna said that smoking anything, even weed starts inflammatory processes that might play a part in the growth of cancer. It is also possible for cannabinoids to cause cancer in the body.
“There are biological reasons to think that cannabis smoke might be bad, but we don’t know what the level of increased risk is, if there is one, with head and neck cancer,” he said, adding that it’s hard to separate cannabis smoke from other risk factors like smoking and drinking. About 20% of the people in the study who had a cannabis use disorder also used marijuana and alcohol often, while only 2% of the people who did not have a cannabis use disorder did.
With this in mind, Hanna said that eating weed might be safer than smoking it, even though he knows that some of his patients use medical marijuana to treat their health problems.
But Califano said there are signs that the higher risk of cancer might be caused by some cannabinoids, not the smoke. This is only a guess until more study proves it.
He said, “Cannabinoids do a lot of things that affect the immune system and other things that are connected to either how cancer grows or how our bodies fight cancer.” “So it’s not crazy to think that the effect on cancer that comes from using cannabis is the same whether you smoke it, vape it, or bake brownies with it.”
Hanna and Califano agree that weed probably has effects on health that are both good and bad. As more is learned about how cannabis affects the body, different cannabinoids may be found to raise or lower the risk of cancer in different ways.
“Some of them may be linked to the growth of cancer, and some may stop the growth of cancer,” Califano said.
