Heavy cannabis smoking and head and neck cancer: what does the research tell us?

New research is adding to evidence that heavy, long-term cannabis smoking may be associated with an increased risk of developing head and neck cancer.

Researchers from the Keck School of Medicine at the University of Southern California have been investigating the possible relationship between cannabis use and cancer. Their work has looked at both lung cancer and cancers of the head and neck.

Of particular interest to our community is an earlier study by the same research group, published in JAMA Otolaryngology–Head & Neck Surgery. It found that people recorded as having cannabis-related dependency or problematic cannabis use had a 3.5 to 5 times greater risk of developing head and neck cancer than people without such a record.

The cancers studied included cancers of the mouth, throat (pharynx), voice box (larynx), oropharynx—including the tonsils and base of the tongue—and salivary glands.

Why might smoking cannabis increase cancer risk?

Cannabis smoke contains some of the same potentially harmful chemicals found in tobacco smoke.

Researchers believe repeated exposure to smoke may cause chronic inflammation and damage to DNA in cells lining the respiratory tract. Over many years, this type of damage can contribute to the development of cancer.

But there are still important unanswered questions

This research does not mean that everyone who has used cannabis has a high risk of developing head and neck cancer.

One of the biggest unanswered questions is the dose relationship. Researchers do not yet know how much cannabis, how often, or for how many years someone would need to smoke before their cancer risk meaningfully increases.

The strongest concerns at present relate to heavy and chronic use, particularly daily or multiple-times-a-day smoking. The researchers say the evidence is much less clear for occasional cannabis use.

There are also questions about different ways of using cannabis. Current evidence has not linked cannabis edibles with lung cancer, although their relationship with other cancers remains uncertain. There is also not yet enough long-term evidence to determine the cancer risk from vaping cannabis or exposure to secondhand cannabis smoke.

What does this mean for our community?

For many years our conversations about preventing head and neck cancer have concentrated on well-established risk factors such as tobacco, alcohol and HPV.

Cannabis smoking may increasingly need to become part of that conversation.

The important message is awareness rather than alarm. The research is developing, and an association does not by itself prove that cannabis caused an individual's cancer.

People who currently smoke cannabis heavily may want to discuss this with their GP or healthcare team, particularly if they also smoke tobacco or have other risk factors for head and neck cancer.

And for those who have already been diagnosed with head and neck cancer, research like this should never become a source of blame. Cancer is complex, and in many cases it is impossible to identify one particular reason why an individual developed the disease.

The takeaway: There is growing evidence that heavy cannabis smoking may increase the risk of head and neck cancer. We still need more research to understand how large that risk is, what level of cannabis exposure matters, and whether different methods of cannabis use carry different risks.