Marijuana Smoking and Cancer Risk
Marijuana smoke contains several of the same cancer causing agents (carcinogens) as tobacco, but in higher concentrations, raising concerns that smoking marijuana may be a risk factor for cancer. Unfortunately, studies are difficult to conduct because some people may not be truthful about their use of marijuana. It is difficult to accurately assess how often it 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, to a smaller butt size, and be inhaled more deeply. This leads to higher concentrations 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 than in cigarettes.
Marijuana smoking is also known to cause damage to lung tissue, resulting in asthma and chronic obstructive lung disease (COPD). Researchers caution that smoking marijuana may also decrease reproductive function and increase the risk of cancer of the mouth and tongue. It may also suppress the body's immune system and 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, the large majority of studies have not found a strong cause and effect related to cancer. This is more likely due to the small studies and the difficulties mentioned above when studying this behavior. The legalization in many areas may help to conduct 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 yet to quantify this with clinical studies.
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.
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