Adults diagnosed with cannabis use disorder were nearly four times as likely to develop lung cancer as matched adults without the diagnosis, according to a large U.S. study in the journal Lung Cancer. The relative risk came out at 3.87.
That wording matters. Cannabis use disorder is a clinical diagnosis, a pattern of heavy, compulsive use that causes real impairment or distress. The study did not look at casual or occasional users, and it does not say what their risk is.
How the study was done
Researchers pulled 20 years of electronic health records from the TriNetX network, which covers more than 118 million patients across 67 health care organizations. Using propensity score matching, a statistical method for building comparable groups, they ended up with nearly 150,000 people in each. The paper appeared on April 22, 2026, and ScienceDaily highlighted it on July 10.
The raised risk held up over time. It was 3.48 at one year after diagnosis and 3.92 at five years. It also showed up in every major type of lung cancer the team examined: small cell carcinoma (2.70), adenocarcinoma (2.54), squamous cell carcinoma (2.90) and non-small cell lung cancer (2.75).
The authors call it the most comprehensive U.S. data so far on marijuana and lung cancer. Earlier work was weaker: small samples, short follow-up, and the tangle of people who smoke both cannabis and tobacco. A 40-year Swedish cohort study had found a two-fold increase for heavy use that began in young adulthood, even after adjusting for tobacco.
What it cannot say
The team could not pin down how much marijuana drives the risk. Nor could it separate out tobacco, vaping or other inhaled exposures that often overlap with the disorder. The study shows an association, not a cause.
Dr. Brooks Udelsman, a thoracic surgeon at Keck Medicine of USC and a co-author, said the link between tobacco and lung cancer is well established while the cannabis picture is far less clear. Growing evidence, he told ScienceDaily, suggests heavy use may carry significant risks. Scientists are still working out the biology. Marijuana smoke contains some of the same combustion carcinogens as tobacco smoke, including benzene, naphthalene and vinyl chlorides, and some research suggests it leaves more tar per cigarette equivalent because users inhale deeply and hold the smoke.
The authors called for more research on dose and mechanism, and said clinicians should weigh these risks when talking with patients about cannabis. Recreational cannabis is now legally sold in 24 states.
What to do
Lung cancer often shows no symptoms early on. A new cough that lasts several weeks, chest pain that worsens with deep breaths, or new shortness of breath should be checked promptly. People who smoke marijuana regularly, especially those who also smoke or have smoked tobacco, can talk to their doctor about lung health. The American Cancer Society recommends annual low-dose CT screening for adults aged 50 to 80 with a 20 pack-year smoking history who still smoke or quit within the past 15 years.
Anyone worried about their own pattern of use can raise it with a health care provider, since cannabis use disorder is a recognized condition with effective treatments, including behavioral therapy.
