As more states within the United States legalize marijuana, many people have begun to focus on the health impacts of smoking it. It is well known that tobacco causes lung cancer, so some people assume marijuana will be the same. The reality is more complex, with various studies showing no direct link between marijuana and lung cancer, but some potentially negative outcomes. Here is some of available research to help you determine if smoking marijuana will increase your lung cancer risk.
The Evidence So Far
One of the problems for researchers looking into this topic is that tobacco is often used by marijuana smokers. Some of the studies below adjust for the increased lung cancer risk from smoking tobacco by using mathematical probabilities.
A 2006 study published in the International Journal of Cancer indicated there was no increase in lung cancer risk for marijuana smokers (Zhang LR, Morgenstern H, Greenland S, Chang S, Lazarus P, Teare MD, Woll PJ, Orlow I, Cox B, Brhane Y, Liu G, Hung RJ, 2006). The research looked at 2,159 people with lung cancer and 2,985 control subjects. It found that after adjusting for tobacco use and sociodemographic factors, there was no evidence for increased lung cancer risk from smoking cannabis.
Another study in the same year looked at 1,212 lung cancer patients and 1,040 controls. It found that lung cancer cannot be associated with long-term marijuana use or the association is so weak it is difficult to detect (Hashibe M, Morgenstern H, Cui Y, Tashkin DP, Zhang Z, Cozen W, Mack TM, Greenland S, 2006).
Some of the studies do point out that some of the components in marijuana smoke are known carcinogens. One meta-study mentions the potential risk of tar in marijuana smoke as a mediator for lung carcinogenesis (Mehra R, Moore BA, Crothers K, Tetrault J, Fiellin DA, 2006), which means the tar can help genetic mutations form in the lungs that may later lead to lung cancer. Because marijuana smokers hold the smoke in their lungs for longer periods, they are exposed to more tar than they would if smoking cigarettes.
The meta-study also points out that benzopyrene, a carcinogen hydrocarbon found in cigarette smoke, is also found in marijuana smoke. Researchers also mention in vitro studies showing THC can induce malignant cell proliferation. Ultimately, the meta-study concluded that more research was required to determine what role marijuana smoke plays in the development of lung cancer.
A more recent study from 2013 declared that marijuana smoking only poses a “relatively small” risk to the lungs (Tashkin DP, 2013). While Dr Tashkin does highlight the increase in symptoms of chronic bronchitis for marijuana smokers, he found that the consumption of marijuana alone did not lead to lung abnormalities. The paper does mention the fact that marijuana contains known carcinogens and cocarcinogens. It is also less optimistic about the outcomes for long term, heavy users of marijuana.
There is some evidence that smoking both cigarettes and marijuana at the same time can increase lung cancer risk, more than smoking cigarettes on their own (University of Washington, 2013). Based on this research, it is healthier to be a smoker than it is to be both a smoker and a cannabis user.
At this stage, there is no definitive link between smoking marijuana and increased lung cancer risk. However, there are some worrying signs like the presence of tar and some carcinogenic compounds in marijuana smoke. There is one thing that is crystal clear from the available research — tobacco should always be avoided, especially so if you smoke marijuana.
Hashibe M, Morgenstern H, Cui Y, Tashkin DP, Zhang Z, Cozen W, Mack TM, Greenland S, (2006). Marijuana Use and the Risk of Lung and Upper Aerodigestive Tract Cancers: Results of a Population-Based Case-Control Study. http://cebp.aacrjournals.org/content/15/10/1829.short
Mehra R, Moore BA, Crothers K, Tetrault J, Fiellin DA (2006). The Association Between Marijuana Smoking and Lung Cancer. http://archinte.jamanetwork.com/article.aspx?articleid=410634
Tashkin DP (2013). Effects of Marijuana Smoking on the Lung. http://atsjournals.org/doi/abs/10.1513/AnnalsATS.201212-127FR?journalCode=annalsats#.VBvaJC6SzUM
University of Washington (2013). Respiratory Effects of Marijuana. http://adai.uw.edu/marijuana/factsheets/respiratoryeffects.htm
Zhang LR, Morgenstern H, Greenland S, Chang S, Lazarus P, Teare MD, Woll PJ, Orlow I, Cox B, Brhane Y, Liu G, Hung RJ (2006). Cannabis smoking and lung cancer risk: Pooled analysis in the International Lung Cancer Consortium. http://onlinelibrary.wiley.com/doi/10.1002/ijc.29036/abstract