Adults diagnosed with cannabis use disorder developed lung or bronchus cancer at 3.87 times the rate of matched adults without the diagnosis, according to a study published April 22, 2026, in the journal Lung Cancer. The 95% confidence interval ran from 3.43 to 4.38.
The researchers drew on 20 years of electronic medical records from 67 U.S. health care organizations in the TriNetX network, which holds data on more than 118 million patients. After propensity score matching, a statistical method for building comparable groups, they had nearly 150,000 participants in each group. Authors are affiliated with the Keck School of Medicine at the University of Southern California, and the team describes it as the most comprehensive U.S. data yet on marijuana and lung cancer.
What the numbers show
The gap did not fade with time. Relative risk was 3.48 at one year after a cannabis use disorder diagnosis and 3.92 at five years. It also appeared across every major lung cancer type: 2.70 for small cell carcinoma, 2.54 for adenocarcinoma, 2.90 for squamous cell carcinoma and 2.75 for non-small cell lung cancer.
Cannabis use disorder is a formal clinical diagnosis. It describes use that causes significant impairment or distress. It is not a measure of occasional use, and the study says nothing about the risk for casual or infrequent users.
Limits the authors acknowledge
The study could not pin down how much marijuana drives the risk. It also could not separate out concurrent tobacco use, vaping or other inhaled exposures that may overlap in people with the disorder. A retrospective record review shows an association, not a cause.
Earlier research on the question was thinner, with smaller samples, shorter follow-up and tobacco use muddying the results. A 40-year Swedish cohort study found that heavy cannabis use starting in young adulthood was tied to roughly double the lung cancer risk, even after adjusting for tobacco.
What the researchers say
Dr. Brooks Udelsman, a thoracic surgeon at Keck Medicine of USC and a co-author, told ScienceDaily that the link between tobacco and lung cancer is well established, while the picture with cannabis is far less clear. Growing evidence, he said, suggests heavy use may carry significant risks. Scientists are still working out the biology. Marijuana smoke contains some of the same combustion products found in tobacco smoke, including benzene, naphthalene and vinyl chlorides.
The authors called for more work on dose-response, and said clinicians should weigh these risks when they advise patients about cannabis. Cannabis is now legally sold for recreational use in 24 states.
Lung cancer often causes no symptoms early on. A new cough that lasts weeks, chest pain that worsens with deep breaths, or new shortness of breath should be checked promptly, especially in anyone who regularly smokes marijuana or tobacco. Consult your doctor for medical advice.
