Excessive marijuana use may increase the risk of multiple types of head and neck cancer, a study warns.
Researchers have found a link between daily cannabis smoking and up to a ninefold increase in several types of mouth, throat and nose cancer.
The study focused only on the most heavy users: those who were so addicted to marijuana that it was affecting their lives.
But experts are concerned about the implications for recreational users.
In the study, the team said it “has important public health implications given that cannabis use is increasing among young adults with trends toward legalization.”
A study published this week found that heavy marijuana users may be up to nine times more likely to develop head and neck cancer.
Federal research has shown that cannabis use is increasing, particularly among Americans under age 30.
Scholars believe cannabis smoke can irritate the upper airways and cause DNA damage that leads to cancer formation.
The findings come just weeks after the Drug Enforcement Administration (DEA) downgraded the legal classification of marijuana.
It was moved from Schedule 1, which has the greatest potential for abuse, to Schedule 3, along with other substances such as ketamine and some anabolic steroids.
Schedule 3 drugs remain controlled substances and subject to rules and regulations, and people who traffic them without a permit could still face federal criminal prosecution.
However, this reclassification will not automatically legalize marijuana throughout the United States. Recreational marijuana is currently legal in 24 states, and 13 allow limited medicinal use.
As the substance becomes legal in more states, use and addiction have also become more prevalent. An NIH-funded study, for example, found that marijuana use among young adults hit an all-time high of one in 12 in 2021.
Rates rose the most in states like California, which legalized recreational cannabis in 2018.
A number of recent studies have linked heavy marijuana use to health problems such as heart attacks, strokes and some types of cancer, including head and neck cancers.
Head and neck cancers, which include cancers of the tongue, tonsils, and gums, are also on the rise, with the National Cancer Institute (NCI) estimating a one percent year-over-year increase since 2012.
Experts believe this could be due to the rise in cases of human papillomavirus (HPV) and increased alcohol consumption, which can stimulate the production of cancer cells.
Recreational marijuana is legal in 24 states, although others have legalized it for medicinal purposes only.
In the new study, published on thursday In JAMA Otolaryngology – Head and Neck Surgery, researchers analyzed data from more than 230,000 adults, half of whom were diagnosed with cannabis use disorder at some point between April 2004 and April 2024.
Those who used marijuana heavily were on average about 42 years old, while the average age of those who did not use marijuana was 60 years old.
Heavy marijuana users were six to nine times more likely to develop different forms of head and neck cancer than non-users.
Overall, cannabis users were three times more likely to develop any form of head and neck cancer.
The highest risk was increased ninefold for laryngeal cancer. This form of the disease, which affects 13,000 Americans and kills about 3,500 a year, is often caused by excessive tobacco and alcohol consumption.
The team believes cannabis aggravates airway cells, leaving them more vulnerable to damage and less able to defend themselves against cancer cells. However, they said further research is needed.
The study had several limitations, notably that it focused solely on heavy marijuana users rather than more casual users. It is also unclear exactly how much marijuana the users consumed and how frequently they picked up the habit.