New research suggests a strong link between long-term daily marijuana use and head and neck cancers.

A recent study analyzing millions of medical records found that individuals with cannabis use disorder—characterized by symptoms such as cravings, tolerance, and withdrawal—are three to five times more likely to develop these cancers compared to non-users.

Cannabis use disorder is diagnosed when a person exhibits two or more symptoms as defined by the US Centers for Disease Control and Prevention, including intense cravings, reduced effects over time, excessive use, continued use despite negative consequences, and difficulty quitting.

According to Dr Niels Kokot, a professor of clinical otolaryngology-head and neck surgery at the Keck School of Medicine at the University of Southern California in Los Angeles, research shows that people who use cannabis, particularly those with a cannabis use disorder, are significantly more likely to develop head and neck cancers compared to those who do not use cannabis.

“While our study did not differentiate between methods of cannabis consumption, cannabis is most commonly consumed by smoking, The association we found likely pertains mainly to smoked cannabis.”

Some 69 percent of people with a diagnosis of oral or throat cancer will survive five years or longer after their diagnosis, according to the National Cancer Institute. If the cancer metastasizes, however, that rate drops to 14 percent. About 61 percent of people diagnosed with cancer of the larynx will be alive five years later – a rate that drops to 16 percent if the cancer spreads.

The study used insurance data to look at the association of cannabis use disorder with head and neck cancers, 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. “The researchers used a huge, huge dataset, which is really extraordinary, and there is enormous power in looking at numbers this large when we typically only see small studies,” said Califano, also the director of University of Californ8a, San Diego’s Hanna and Mark Gleiberman Head and Neck Cancer Center.

“On average, people with cannabis use disorder smoke about a joint a day and do so for at least a couple years, if not longer,” said Califano, who coauthored an editorial published in JAMA Otolaryngology-Head & Neck Surgery in conjunction with the new study.

However, he added, the study does not find an association between “the occasional recreational use of marijuana and head and neck cancer.”