USC studies link heavy marijuana smoking to multiple cancers
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- Keck Medicine of USC study led by otolaryngologist Niels Kokot found that people who smoked large amounts of marijuana appeared to face a higher risk of both small cell lung cancer and non-small cell lung cancer.
- Kokot and colleagues reported in a 2024 JAMA Otolaryngology–Head study that daily marijuana users were 3.5 to 5 times more likely to develop head and neck cancers — including mouth, pharynx, larynx, oropharynx, and salivary gland cancers — than nonusers.
- Thoracic surgeon Brooks Udelsman said the dose-response relationship remains unknown: occasional use likely carries minimal risk, but chronic heavy users who develop dependency appear to face cancer risks similar to tobacco smokers.
- Edibles have not been linked to lung cancer so far, per Udelsman, though data is limited and links to other cancer types are still being investigated.
- THC, marijuana's primary psychoactive ingredient, is associated with conversion of polycyclic aromatic hydrocarbons that trigger inflammation and DNA damage, according to Udelsman, who notes marijuana smoke shares roughly 70 carcinogenic chemicals with tobacco smoke.
- Vaping marijuana carries unknown long-term cancer risks because vaping has only been common for about 15 years, though inflammatory lung diseases are already surfacing.
- Researchers are also investigating potential links between heavy marijuana use and bladder cancer and gastrointestinal cancers.
Why it matters: For daily heavy marijuana users — those with dependency or requiring hospital care — the emerging cancer risk profile appears to mirror chronic tobacco smokers, particularly for small cell lung cancer where inhalational injury is almost always present. With legalization expanding and edibles showing no lung cancer link, the findings give users and clinicians a concrete basis for risk conversations even as dosing thresholds remain undefined.
