People who frequently use marijuana more than triple their risk of developing oral cancer, a new study found.
About half of US adults say they have ever tried marijuana, with about 17.7million suffering from symptoms of cannabis use disorder (CUD).
The condition requires a formal diagnosis after fulfilling several criteria, such as using the drug despite the negative impacts it has on a person’s life and relationships.
University of California, San Diego researchers followed 45,000 people, some with cannabis use disorder, for five years. They discovered that daily smokers were 3.25 times more likely to develop oral cancer than those without the disorder.
Dr Raphael Cuomo, an anesthesiology professor at UC San Diego School of Medicine who led the analysis, said: ‘Cannabis smoke contains many of the same carcinogenic compounds found in tobacco smoke, which have known damaging effects on the epithelial tissue that lines the mouth.’
Cannabis smoke packs a heavy load of toxic chemicals and carcinogens, about 2,600 of them, similar to tobacco smoke.
But researchers are only recently getting a fuller understanding of what those chemicals are. They now know that marijuana smoke contains hundreds of polycyclic aromatic hydrocarbons (PAHs), benzene, and ammonia.
These chemicals adhere to mucus membranes in the mouth, enabling carcinogens to seep into oral tissue. Meanwhile, THC, the psychoactive chemical in marijuana, can suppress crucial immune system pathways that would typically patrol for, and kill, those rogue cells.
Nearly 18 million Americans are daily or near-daily cannabis users, which researchers have found increases the risk of oral cancer by more than three times
Of the more than 45,000 patients included in the study, 949 had cannabis use disorder.
The group that did not smoke or smoked only occasionally remained either weed free or only occasional users over the five-year study. Over 97 percent were still abstinent or infrequent users by the time researchers followed up.
During the study, 106 patients were diagnosed with oral cancer. Among people without CUD, the rate of oral cancer was 0.23 percent, which matches general population rates.
However, among participants with CUD, 0.74 percent developed oral cancer.
Oral cancer includes cancerous growths that develop in the mouth and throat, including the lips, tongue, gums, the floor of the mouth and the roof of the mouth.
About one in 59 men and 1 in 139 women will develop oral cancer at some point in their lives.
Oral cancers account for about three percent of cancers diagnosed in the US every year, with about 58,500 diagnoses and 12,250 deaths annually.
Researchers said their findings will have implications for cancer screening practices in primary care and mental health settings, as patients with CUD often present with overlapping social and behavioral risk factors, including tobacco use, alcohol use, and a lower likelihood of engaging in preventive healthcare.
People with CUD who were also tobacco users were 6.24 times more likely to get oral cancer. Age also played a role, with each additional year of age increasing cancer risk by about four times per year.
Like tobacco smokers, marijuana smokers see damage to their lung and throat cells, leading to abnormal cell growth that can cause cancer and tissue changes.
Those effects can occur in people who are not tobacco smokers, though, indicating that marijuana smoke can be just as harmful on its own as cigarette smoke.
Dr Cuomo said: ‘These findings add to a growing body of evidence suggesting that chronic or problematic cannabis use may contribute to cancer risk in tissues exposed to combustion products.’
Their findings were published in the journal Preventive Medicine Reports.
In the United States, marijuana is fully legal for recreational and medicinal use in 29 states. It is entirely illegal in four states.
The majority of the public, about 88 percent, supports legalization, according to the Pew Research Center. But public health experts are raising concerns over potential long-term effects, of which scientists still do not have a complete understanding.
In June, University of California researchers reviewed 24 studies involving 200million people to investigate the relationship between weed and cardiovascular disease, stroke and acute coronary syndrome (ACS) – a group of heart conditions in which there is reduced or blocked blood flow to the heart, such as a heart attack.
They found there was a 29 percent higher risk of ACS among cannabis users, a 20 percent higher risk for stroke and double the risk of dying from cardiovascular disease, which includes coronary artery disease, heart failure and irregular heartbeats.
Last month, findings from an FDA-run clinical trial were released, investigating dangerous liver enzyme spikes in people who consumed cannabis.
Cannabis is becoming easier to access and more potent. The graph refers to smokable cannabis. Other forms, such as vapes, contain up to 98 percent of THC, the psychoactive chemical in the drug linked to psychosis
The results showed that eight users of CBD, the substance derived from the hemp plant that’s free of the psychoactive chemical THC, developed enzyme spikes above the safe threshold, raising the risk of chronic liver damage or failure.
Seven people dropped out due to liver concerns between weeks three and four.
However, everyone’s liver tests normalized after quitting CBD.
Meanwhile, regular use of potent cannabis in adolescence has been linked to long-term changes in brain structure, particularly in the prefrontal cortex, the region responsible for decision-making, emotional regulation, and impulse control.
This is also the age when many psychotic disorders first appear.
THC may trigger schizophrenia or psychotic episodes in individuals with genetic predispositions.
A 2022 review by University of Bath researchers, which analyzed 20 studies involving 120,000 people, found users of high-potency cannabis were four times more likely to develop addiction and three to five times more likely to suffer a psychotic break compared to those using lower-potency strains.
Earlier this year, a report in JAMA Network Open found that emergency room visits in Ontario, Canada, linked to schizophrenia in marijuana users tripled after legalization.
Between 2006 and 2022, the rate of schizophrenia among those with cannabis use disorder climbed from four percent to over 10 percent. In contrast, just 0.6 percent of non-users developed the condition.
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