(CNN) — Years of daily marijuana use may increase the overall risk of head and neck cancer by three to five times, according to a new study that analyzed millions of medical records.
“Our research shows that people who use cannabis, particularly those with cannabis use disorder, are significantly more likely to develop head and neck cancer than people who do not use cannabis,” said lead study author Dr. Niels Kokot, professor of clinical otolaryngology and head and neck surgery at the Keck School of Medicine at the University of Southern California in Los Angeles.
Cannabis use disorder occurs when a person has two or more of the following symptoms, including craving weed, tolerance to the effects, using more than intended, using marijuana even though it is causing problems in life, using in high-risk situations, experiencing withdrawal symptoms and an inability to stop using, according to the U.S. Centers for Disease Control and Prevention.
“Although our study did not distinguish between methods of cannabis consumption, cannabis is most commonly consumed through smoking,” Kokot said in an email. “The association we found likely relates primarily to smoked cannabis.”
About 69% of people diagnosed with oral or pharyngeal cancer survive five years or more after diagnosis, according to the National Cancer Institute. However, if the cancer metastasizes, that rate drops to 14%. About 61% of people with laryngeal cancer are still alive five years later—a rate that drops to 16% if the cancer spreads.
The study used insurance data to examine the link between cannabis use disorder and head and neck cancer, said Dr. Joseph Califano, the Iris and Matthew Strauss Chancellor’s Endowed Chair in Head and Neck Surgery at the University of California, San Diego. He was not involved in the study.
“The researchers used a huge data set, which is really extraordinary, and it’s tremendously insightful to look at such large numbers when we usually only see small studies,” said Califano, who is also director of the Hanna and Mark Gleiberman Head and Neck Cancer Center at UC San Diego.
“On average, people with cannabis use disorder smoke about one joint today and continue to do so for at least a few years, if not longer,” said Califano, co-author of an editorial published Thursday in JAMA Otolaryngology–Head & Neck Surgery related to the new study.
However, he added that the study could not establish a link between “occasional recreational marijuana use and head and neck cancer.”
Causes of head and neck cancer
In the United States, head and neck cancer accounts for 4% of all cancers, and more than 71,000 new cases and more than 16,000 deaths are expected in 2024, according to the National Foundation for Cancer Research..
Tobacco use, including smoking cigarettes, cigars, pipes and smokeless tobacco, and alcohol consumption are the two most common causes of head and neck cancer, according to experts. Other risk factors include poor oral hygiene; gastroesophageal reflux disease (GERD); a weakened immune system; and a diet low in fruits and vegetables. Occupational risk factors include exposure to asbestos and wood dust.
An increasing number of head and neck cancers are caused by infections with the human papillomavirus (HPV) or the Epstein-Barr virus (EBV). These are DNA viruses that attack genes, making them susceptible to malignant diseases.
The Epstein-Barr virus is associated with infectious mononucleosis, also known as the “kissing disease,” as well as several types of cancer. Researchers estimate that 90% of the world’s population is infected with EBV. There is a vaccine against HPV, which is associated with a high risk of developing cervical cancer and some non-Hodgkin lymphomas.
Simultaneous infection with both viruses is possible. Research shows that this combination is responsible for 38% of all virus-related cancers.
How can cannabis cause cancer?
The study published on Thursday in JAMA Otolaryngology–Head & Neck SurgeryAanalyzed a database of 4 million electronic health records and found more than 116,000 diagnoses of cannabis use disorder in people with head and neck cancer. These men and women, whose average age was 46, were then compared with people who also had head and neck cancer but were not diagnosed with cannabis use disorder.
TThe analysis found that people with cannabis use disorder were about 2.5 times more likely to develop oral cancer; almost five times more likely to develop oropharyngeal cancer, i.e. cancer of the soft palate, tonsils and throat; and over eight times more likely to develop laryngeal cancer. The results apply to all age groups, according to the study.
Experts say smoking is a major reason for the link between marijuana use and head and neck cancer. Tobacco use doubles the risk of developing squamous cell carcinoma of the head and neck, which accounts for 90% of all head and neck cancers. Heavier tobacco use increases the risk even more, and when alcohol is added, the risk is even greater.
Because of the way marijuana is smoked — unfiltered, inhaled deeply and held in the lungs and throat for several seconds — the risk from cannabis smoke may be even greater, experts say.
Another key to the mystery of how cannabis causes cancer: Research has found a link between various cannabinoids and tumor growth. According to the National Center for Complementary and Integrative Health, there are more than 100 cannabinoids—biological compounds that bind to cannabinoid receptors in the human body—in the cannabis plant. In total, there are about 540 chemicals in each marijuana plant.
Tetrahydrocannabinol (THC) is the substance that has a euphoric effect, while cannabidiol (CBD) has been shown to have medical uses in the treatment of seizures and epilepsy in childhood.
“Some of the research we’ve already published shows that THC or THC-like compounds can indeed accelerate tumor growth,” said Califano. “We also have some data showing that cannabinoids promote the growth of HPV-related laryngeal cancer.””
With marijuana use on the rise, there are concerns that the number of head and neck cancer diagnoses could increase in the coming years, Kokot said.
“Particularly as (marijuana) becomes increasingly legalized and socially accepted, we could see a corresponding increase in head and neck cancer cases if the link is confirmed,” he said.
“This highlights the importance of educating people about the potential risks and conducting further research to understand the long-term effects of cannabis use on cancer development.”
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