Marijuana Use May Raise Lung Cancer Risk, Researchers Warn

As marijuana legalization continues to expand across the US, questions surrounding the long-term health effects of cannabis use are becoming increasingly important. Although the relationship between tobacco smoking and lung cancer is well established, researchers say the connection between marijuana smoking and cancer remains less defined—but growing evidence suggests heavy use may carry significant risks.^1,2

A retrospective cohort study published in Oral Oncology found that individuals with cannabis use disorder had significantly increased odds of developing both small cell and non–small cell lung cancer compared with nonusers.² The findings add to a growing body of literature suggesting chronic marijuana smoking may contribute to cancer development through mechanisms similar to those associated with tobacco smoke.

New Evidence Links Heavy Cannabis Use to Lung Cancer

The study, led by investigators at the University of Southern California, evaluated associations between cannabis use disorder and lung cancer diagnoses. Using large-scale patient data, they observed elevated risks for both major forms of lung cancer, particularly among individuals with heavy or chronic marijuana exposure.^1,2

According to Brooks Udelsman, MD, a thoracic surgeon with Keck Medicine of USC, one of the largest unanswered questions is determining the dose-response relationship between marijuana use and cancer risk.¹

“What we don’t know right now is the dose-[response] relationship,” Udelsman said. “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.”¹

Udelsman noted that current evidence primarily points toward risks among patients with chronic, heavy exposure. “Those are the people data today show are at risk for developing cancer, similar to tobacco,” he explained.¹

Researchers also emphasized that the risk profile may differ substantially depending on how marijuana is consumed. Current evidence does not show a clear relationship between edible cannabis products and lung cancer risk, although investigators say additional long-term data are still needed.¹

Shared Carcinogens Between Tobacco and Marijuana Smoke

Experts say marijuana smoke contains several harmful chemicals also found in tobacco smoke.¹ Tobacco smoke contains more than 7000 chemicals, including dozens of known carcinogens.³ Some of these compounds—including polycyclic aromatic hydrocarbons—are also present in marijuana smoke and may contribute to inflammation and DNA damage.¹

“Any time inflammation and changes to DNA occur, you’re at risk for developing cancer,” Udelsman said.¹

Additionally, smoking marijuana often involves deeper inhalation and longer breath-holding compared with tobacco use, potentially increasing exposure to harmful particulates. Previous studies have demonstrated that marijuana smoke can produce airway inflammation and histopathologic changes similar to those observed in tobacco smokers.⁴

The findings come at a time when marijuana use continues to rise nationally. According to the CDC, cannabis is one of the most commonly used psychoactive substances in the US, particularly among younger adults.⁵

Implications for Pharmacists and Patient Counseling

For pharmacists, the growing evidence surrounding marijuana-related cancer risks may become increasingly relevant during patient counseling, particularly as cannabis products become more accessible through medical and recreational legalization.

Patients may perceive marijuana as inherently safer than tobacco because of its legal status or medicinal applications. However, clinicians should educate patients that inhaled marijuana smoke may still expose the lungs to inflammatory and carcinogenic compounds.^1,3

Researchers caution that additional long-term studies are needed to fully understand the relationship between marijuana use, dosage, vaping, and cancer risk. Still, experts say the current evidence supports counseling patients—especially those with chronic heavy use—about potential pulmonary complications and the importance of discussing cannabis habits with their health care providers.¹

REFERENCES

1. Keck School of Medicine of USC. Marijuana use may raise lung cancer risk, researchers warn. SciTechDaily. May 15, 2026. Accessed May 19, 2026. https://scitechdaily.com/marijuana-use-may-raise-lung-cancer-risk-researchers-warn/

2. Gallagher TJ, Kokot NC, Lopez J, et al. Association of cannabis use and lung cancer: a retrospective cohort study. Lung Cancer. 2026;216:109421. doi:10.1016/j.lungcan.2026.109421

3. Marijuana and lung health. American Lung Association. Updated July 16, 2025. Accessed May 19, 2026. https://www.lung.org/quit-smoking/smoking-facts/health-effects/marijuana-and-lung-health

4. Tashkin DP. Effects of marijuana smoking on the lung. Ann Am Thorac Soc. 2013;10(3):239-247. doi:10.1513/AnnalsATS.201212-127FR

5. About cannabis. CDC. February 15, 2024. Accessed May 19, 2026. https://www.cdc.gov/cannabis/about/index.html