Heavy cannabis use may increase risk of certain cancers, new study finds

Research linked the drug to a greater risk of head and neck cancers.

A recent study published in JAMA Otolaryngology-Head & Neck Surgery has linked regular heavy cannabis use to a heightened risk of developing head and neck cancers. According to the research, individuals who use cannabis heavily are 3.5 to 5 times more likely to develop these cancers compared to those who do not use the drug regularly.

Head and neck cancers, which affect the mouth, throat, and nasal cavity, are notably more common in men than in women, as reported by the Centers for Disease Control and Prevention (CDC). This study contributes to an emerging body of evidence exploring the impact of cannabis on cancer risk.

Dr. Niels Kokot, the lead author and a head and neck surgeon at Keck Medicine of the University of Southern California, explained that the risk could stem from either the cannabinoids themselves or the carcinogenic potential of cannabis smoke. Kokot’s team analyzed two decades of data from the TriNetX global database, which included information from 64 health centers across the U.S. Out of over 4 million individuals studied, approximately 116,000 had been diagnosed with cannabis use disorder between April 2004 and April 2024. This diagnosis was based on patients’ self-reported cannabis use.

The study compared those with cannabis use disorder to similar-aged and sex-matched individuals without such a diagnosis. The cannabis users showed a greater likelihood of developing various head and neck cancers, except for hypopharyngeal cancer, which affects the lower throat. The most common cancers observed were oral and laryngeal cancers.

The authors noted limitations in their findings, such as the challenge of accurately measuring regular cannabis use from self-reported data. To be categorized in the heavy use group, individuals had to report using cannabis very frequently, approximately equivalent to smoking one joint per day.

Dr. Joseph Califano, director of the Gleiberman Head and Neck Cancer Center at Moores Cancer Center, who was not involved in the study, pointed out the difficulties inherent in studies on cannabis use due to the lack of comprehensive data. He also highlighted the challenges in accounting for concurrent alcohol and tobacco use.

The study further analyzed cancer diagnoses at two intervals: within the first year and five years or more after a cannabis use disorder diagnosis. Cancers diagnosed between one and four years were excluded to strengthen the association's validity. After five or more years, the cannabis use disorder group still had elevated overall rates of head and neck cancer, though the risk for specific cancers like oral, laryngeal, and oropharyngeal cancers was no longer significantly higher.

Dr. Glenn Hanna, a medical oncologist at the Dana-Farber Cancer Institute, acknowledged the potential for cannabis smoke to activate inflammatory pathways that might contribute to cancer development. However, he also noted the difficulty of isolating the impact of cannabis use from other risk factors such as alcohol and tobacco. Approximately 20% of those with cannabis use disorder in the study reported frequent use of tobacco and alcohol, compared to about 2% in the non-use disorder group.

Hanna suggested that consuming cannabis in edible form might be safer than smoking. Califano also raised the possibility that cannabinoids themselves, rather than just the smoke, could contribute to cancer risk, though further research is needed to clarify this.

Both experts agree that cannabis likely has a mix of positive and negative health effects. Future research may reveal that different cannabinoids have varying impacts on cancer risk, with some potentially inhibiting cancer development while others could contribute to it.