Marijuana Smoking and Cancer Risk
Marijuana smoke contains several of the same cancer-causing agents (carcinogens) as tobacco but in higher amounts. This raises the concern that smoking marijuana may be a risk factor for cancer. Unfortunately, studies are hard to do because some people may not be truthful about their use of marijuana. It is hard to know how often marijuana is used and the amount of exposure over many years. In addition, many individuals who use marijuana also smoke tobacco.
Marijuana cigarettes tend to be smoked without filters, are inhaled more deeply, and are smoked to a smaller butt size. This leads to higher amounts of smoke being drawn deeper into the lungs than with cigarette smoking. Marijuana smoke leads to 5 times greater absorption of carbon monoxide than cigarettes. Due to how long marijuana smoke is held in the lungs, there is 4x more tar deposited in the lungs. Benzopyrene, a cancer-causing agent, is present in similar amounts in marijuana as in cigarettes.
Marijuana smoking is also known to damage lung tissue, leading to asthma and chronic obstructive lung disease (COPD). Researchers warn that smoking marijuana may also decrease reproductive function (the ability to have a baby) and can increase the risk of cancer of the mouth and tongue. Marijuana may weaken the body's immune system and may increase the risk of leukemia and other cancers in children whose mothers smoke marijuana during pregnancy.
Despite all that we know about the dangers of marijuana smoke, most of the studies have not found a strong link to cancer. This is more likely due to the small size of the studies and the difficulties mentioned above when studying marijuana use. Marijuana legalization in many areas may offer better quality studies going forward. The bottom line is, researchers agree that there is most likely some cancer-causing effect to smoking marijuana, but they have not been able to capture this in numbers with clinical studies yet.
Callaghan, R. C., Allebeck, P., Akre, O., McGlynn, K. A., & Sidorchuk, A. (2017). Cannabis Use and Incidence of Testicular Cancer: A 42-Year Follow-up of Swedish Men between 1970 and 2011. Cancer Epidemiology and Prevention Biomarkers, 26(11), 1644-1652.
Centers for Disease Control. Marijuana and Public Health. 2017.
Hashibe, M., Straif, K., Tashkin, D. P., Morgenstern, H., Greenland, S., & Zhang, Z. F. (2005). Epidemiologic review of marijuana use and cancer risk. Alcohol, 35(3), 265-275.
Huang, Y. H. J., Zhang, Z. F., Tashkin, D. P., Feng, B., Straif, K., & Hashibe, M. (2015). An epidemiologic review of marijuana and cancer: an update. Cancer Epidemiology and Prevention Biomarkers, 24(1), 15-31.
Marijuana and Cancer from the American Cancer Society.