Studies suggest heavy marijuana smoking could raise cancer risk, but researchers are still working to understand the long-term effects and the role of dosage.
As marijuana becomes legal in more states, many people are asking whether it is actually safe. While the link between tobacco smoking and lung cancer is well established, the connection between marijuana use and cancer remains less clear, according to Brooks Udelsman, MD, a thoracic surgeon with USC Surgery, part of Keck Medicine of USC.
Researchers are continuing to investigate whether marijuana smoking raises the risk of lung cancer. A recent Keck Medicine study led by Niels Kokot, MD, an otolaryngologist with the USC Caruso Department of Otolaryngology – Head and Neck Surgery, found that heavy marijuana smokers may face a greater risk of both small cell and non-small cell lung cancer.
Another study led by Dr. Kokot found that people who use marijuana daily are 3.5 to 5 times more likely to develop head and neck cancers compared to nonusers. These cancers include those affecting the mouth, pharynx, larynx, oropharynx (tongue and tonsils and back wall of the throat), and nearby salivary glands.
Heavy Marijuana Use and Lung Cancer Concerns
As studies continue, Dr. Udelsman says one major unanswered question is how much marijuana use increases cancer risk.
“What we don’t know right now is the dose relationship,” he says. “So, if someone smokes marijuana occasionally once a week, once a month, or a few times a year, do they still have that same risk? My suspicion is that there is probably minimal risk. All we know right now is that people who smoke a lot of marijuana—to the point that they develop a dependency on it or require hospital care or evaluation for it—do appear to have a higher cancer risk.”
Researchers are also examining whether marijuana use could be linked to other cancers, including bladder and gastrointestinal cancers, Dr. Udelsman says.
“With tobacco, we do see an increased prevalence of bladder cancer. Whether that relationship is also the same for heavy marijuana smoking, we don’t know,” he says. “That’s why we’re trying to determine what the risks are so that people can know what risks they’re taking,” he says.
Is marijuana intake through non-smoking methods (consuming edibles, etc.) also associated with a risk of getting lung cancer?
“Probably not,” says Dr. Udelsman. “The risk is harder to track because there isn’t a lot of data on it yet, but as of now there does not seem to be a relationship between edibles and lung cancer. We don’t yet know if there is a link to other types of cancers, however.”
Which components in marijuana smoke can cause cancer?
Dr. Udelsman says anything that causes long-term inflammation can raise cancer risk. Tobacco smoke contains more than 7,000 chemicals, around 70 of which are linked to cancer. Some of those same chemicals are also found in marijuana smoke.
He adds that THC (tetrahydrocannabinol), marijuana’s main psychoactive ingredient, is connected to the conversion of polycyclic aromatic hydrocarbons (PAHs). PAHs may trigger inflammation and damage DNA. “Anytime inflammation and changes to DNA occur, you’re at risk for developing cancer,” he says.
Is secondhand marijuana smoke also linked to lung cancer?
There is not enough evidence yet to confirm a direct link between secondhand marijuana smoke and lung cancer. However, Dr. Udelsman says breathing in secondhand smoke could still increase risk because it exposes people to inflammatory particles associated with cancer development.
Are certain types of lung cancer more common with smoking marijuana?
The two primary forms of lung cancer are small cell lung cancer and non-small cell lung cancer.
Small cell lung cancer is strongly associated with tobacco smoking and may also be connected to marijuana smoking, Dr. Udelsman says. “It’s almost unheard of to get small cell lung cancer without some type of inhalational injury,” he adds.
Researchers have also found higher rates of non-small cell lung cancer among people who smoke either tobacco or marijuana compared to nonsmokers. “We also see an increase in non-small cell lung cancer in smokers of both tobacco and marijuana, so both types are increased when compared to nonsmokers,” Dr. Udelsman says.
Does vaping marijuana cause lung cancer?
Vaping marijuana may carry risks as well, although researchers still do not have enough long-term data to determine whether it directly causes lung cancer. When vaping products first became popular, many people assumed vaping tobacco was safer than smoking traditional cigarettes. However, doctors are now seeing serious inflammatory lung conditions associated with vaping. “But we are starting to see some very severe inflammatory diseases—not cancers, but benign diseases—from vaping,” Dr. Udelsman says.
Because vaping has only been common for about 15 years, researchers say more time is needed to understand whether vaping tobacco or marijuana contributes to lung cancer, since the disease often develops over decades.
“The data on vaping is very new, so we don’t know yet, but I’d worry about anything you’re breathing into your lungs because it infiltrates the cells and air sacs in your lungs, which can cause damage and put you at a higher risk for cancer,” Dr. Udelsman says.
How much marijuana smoking is dangerous?
Dr. Udelsman says occasional recreational marijuana use is unlikely to create a major public health crisis involving lung cancer.
“I worry less about occasional use and the slight inflammation that it might cause for a temporary period. Your body probably recovers from that very quickly, with very little damage,” he says. “I’m more worried about chronic, heavy exposure: people who are using marijuana every day, multiple times a day. That’s where I think you can start to build up injury. Those are the people data today shows are at risk for developing cancer, similar to tobacco.”
People who smoke marijuana heavily should talk with their doctor about their risk factors and whether additional medical evaluation may be appropriate.
Reference: “Association of cannabis use and lung cancer: a retrospective cohort study” by Tyler J. Gallagher, Niels C. Kokot, Joshua Lopez, Eddie Rodriguez, Brooks V. Udelsman, Sean C. Wightman, Scott M. Atay, Takashi Harano, Graeme M. Rosenberg, Jorge J. Nieva and Anthony W. Kim, 22 April 2026, Lung Cancer.
DOI: 10.1016/j.lungcan.2026.109421
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