• Cannabis use is associated with greater risk of developing head and neck cancer, according to a new study.
• Participants had to meet criteria for cannabis use disorder, but the study didn’t include specific information on cannabis consumption.
• Prior research on the association between cannabis consumption and head and neck cancer has been inconsistent.

Cannabis use is strongly associated with the development of head and neck cancer, concludes a sweeping retrospective study of two decades of medical records.

Tobacco and alcohol are already two well-known risk factors for developing head and neck cancers, which include oral and throat cancer. Yet prior research on the risks of cannabis on these cancer types has been inconsistent.

Like tobacco, smoking is a popular way to consume cannabis. Smoking cannabis is known to result in some of the same chemical components as tobacco smoke, which can cause inflammation in the mouth, throat, and lungs — a known cancer risk factor.

A new study published August 8 in the journal JAMA Otolaryngology-Head & Neck Surgery found that cannabis users who met the criteria for cannabis use disorder (CUD) were between 3.5 and 5 times more likely to develop any form of head and neck cancer than those without CUD.

“Our study is the first and the largest to show that there is this association,” said Niels Kokot, MD, a head and neck surgeon with Keck Medicine of USC, and senior author of the study.

“I would consider this a starting point to truly define what the risk is of developing head and neck cancer from cannabis use. It creates an association, but we definitely have more work to do in terms of truly defining what those risk levels are,” Kokot told Healthline.

Head and neck cancer risk 5 times higher among cannabis users

Kokot and his team utilized health records for millions of patients across 64 healthcare organizations in the United States over 20 years.

Among the patients included in the study, 116,076 had a diagnosis of CUD, while nearly 4 million did not.

Patients had no prior history of head and neck cancer. However, there were some demographic differences between those with CUD and those without.

The CUD group skewed younger, with an average age of 46 years old, compared with an average age of 60 in the other group. There were also slightly less women among those diagnosed with CUD (44.5% versus 54.5%).

Researchers then investigated the risk of developing any form of head and neck cancer and site-specific cancers in the two groups.

To strengthen any association, the study used multiple timeframes: 1 year and 5 years between cancer development and CUD diagnosis, and any amount of time between the two events.

Depending on the timeframe, patients with CUD were 3.5 to 5 times more likely to develop any form of head and neck cancer.

Laryngeal cancer, a form of throat cancer, had the strongest individual association with CUD and carried more than an 8-fold increased risk.

Oropharyngeal cancer, a throat cancer that affects the pharynx, showed a nearly 5-fold increase. These findings are similar to prior studies that examined the risk of smoking tobacco and head and neck cancer risk.

Other cancers, including oral, salivary gland, and nasopharyngeal, were associated with a 2–3 times increased risk.

Cannabis consumption, dosage not understood

Despite the strength of the findings, the study does contain some significant limitations, which Kokot acknowledged.

Hospital health records do not contain specific information about a patient’s cannabis use frequency, dose, or route of administration, only that they were diagnosed with CUD.

The authors also note that CUD is likely associated with tobacco and alcohol use, a potential confounding factor. Although they attempted to control for these variables, they note “differences in dosage…may remain” between those diagnosed with CUD and those who were not.

John B. Sunwoo, MD, director of Head and Neck Cancer Research at Stanford Medicine, told Healthline the study was robust but agreed it had some limitations. Sunwoo wasn’t affiliated with the research.

“[The researchers] did not have information about tobacco and alcohol dosages, so we do not know if the cannabis group smoked more,” Sunwoo told Healthline.

Since the study relied only on medical records that indicated a patient had CUD, additional details about cannabis use, including frequency, potency, and route of consumption are not present. As a result, the different types of cannabis consumption, such as smoking versus eating were not able to be differentiated.

“In terms of actually looking at the type of usage, such as edibles versus inhaled, or the amount per day or the amount per week and the number of years, we didn’t have that information within the database that we looked at,” Kokot said.

Questions surrounding whether smoking cannabis is more harmful than ingesting it remain unanswered. There is also no clear threshold for the frequency of cannabis use and an association with increased risk of head and neck cancer.

“We can’t draw any conclusions about those factors,” Kokot said. “That’s where additional information would be needed in the next step of research to try to really parse out the risk level in different types of consumption and quantity of consumption.”

Prior research on cannabis, head and neck cancer inconsistent

Tobacco is recognized as the greatest risk factor for developing head and neck cancer. Alcohol consumption is associated with up to a 5-fold increase in risk for various forms of head and neck cancer.

Individuals who consume both alcohol and tobacco together have a substantially higher risk of developing head and neck cancer.

Meanwhile, studies investigating the association between cannabis and head and neck cancer have been inconsistent, explained Paul Armentano, deputy director of the National Organization for the Reform of Marijuana Laws (NORML). This lack of robust evidence is also acknowledged by the study authors.

For instance, a 2015 study found no association between cannabis usage and the development of head and neck cancer. Another study from 2009, found an inverse relationship between the two, indicating that “moderate” cannabis consumption was associated with reduced risk of developing head and neck cancer.

“Given these historically inconsistent results and the potential issue of confounding, further research is necessary before drawing any sort of definitive conclusions,” Armentano told Healthline.

“In the interim, those who consume cannabis regularly — such as medical cannabis patients — may wish to consider alternative delivery methods that either reduce or eliminate the intake of combustive smoke,” he noted.

Sunwoo shared a similar opinion. “There are limitations for the study, and I think people should be aware of those limitations,” he said. “But I also think it should encourage people to investigate this further because we just don’t know.

Understanding cannabis use disorder

CUD is recognized as a psychiatric disorder, however, the criteria for meeting the diagnosis can be murky, leaving the diagnosis largely at the discretion of a doctor.

To meet the criteria, a patient must meet 2 out of 11 criteria. These include:

• taking large amounts of cannabis
• cravings for cannabis
• withdrawal symptoms when not using cannabis
• persistent desire to cut down with unsuccessful attempts
• continued usage despite social or interpersonal problems
• tolerance

Frequency or quantity of use are not objectively defined as part of CUD diagnosis.

Takeaway

New research found that cannabis use disorder (CUD) was associated with a 3.5 to 5 fold increase in risk of developing head and neck cancer.

Certain site-specific forms of cancer, such as throat (laryngeal), showed up to an 8-fold increase in risk associated with CUD.

Prior studies on the association between cannabis use and these cancer types have been inconsistent. More studies are needed to determine whether ingesting cannabis could have the same impact on head and neck cancer risk as smoking it.