The link between smoking tobacco and lung cancer is undeniable, but does smoking marijuana cause lung cancer, too? The short answer -- probably.
In 2006, many of us in medicine were shocked when a review of research to date did not show an increase in lung cancer related to marijuana use. There was even a suggestion that marijuana had a protective effect against lung cancer. Recent studies, in contrast, do appear to link smoking marijuana with lung cancer.
One study demonstrated a doubling in lung cancer for male marijuana smokers who also used tobacco. Another study found that long-term use of marijuana increased the risk of lung cancer in young adults (55 and under), with the risk increasing in proportion to the amount of marijuana smoked.
Why the controversy?
Since marijuana is illegal, it is hard to do the controlled studies that have been done with tobacco. Because of this, it helps to look at what we do know about marijuana:
- Many of the carcinogens and co-carcinogens present in tobacco smoke are also present in smoke from marijuana.
- Marijuana smoking does cause inflammation and cell damage, and it has been associated with pre-cancerous changes in lung tissue.
- Marijuana has been shown to cause immune system dysfunction, possibly predisposing individuals to cancer.
Bottom line: Though marijuana most likely pales in cancer risk when compared to cigarette smoking, it's better to play it safe. There are reasons in addition to lung cancer risk (and the fact that it is illegal) to avoid marijuana. Marijuana likely increases the risk of testicular cancer, prostate cancer, cervical cancer, a type of brain tumor, and the risk of leukemia in the offspring of women who use it during pregnancy.
Sources:
Aldington, S. et al. Cannabis use and risk of lung cancer: a case-control study. The European Respiratory Journal. 2008. 31(2):280-6.
American Cancer Society. What Causes Small Cell Lung Cancer? Marijuana. 11/13/08. http://www.cancer.org/docroot/CRI/content/CRI_2_2_2x_What_Causes_Small_Cell_Lung_Cancer.asp
Berthiller, J. et al. Cannabis smoking and risk of lung cancer in men: a pooled analysis of three studies in Maghreb. Journal of Thoracic Oncology. 2008. 3(12):1398-403.
Chen, A. et al. Hypothesizing that marijuana smokers are at a significantly lower risk of carcinogenicity relative to tobacco-non-marijuana smokers: evidence based on reevaluation of current literature. Journal of Psychoactive Drugs. 2008. 40(3):263-72.
Hashibe, M. et al. Epidemiologic review of marijuana use and cancer risk. Alcohol. 2005. 35(3):265-75.
Mehra, R. et al. The association between marijuana smoking and lung cancer: a systematic review. Archives of Internal Medicine.
Sarafian, T. et al. Oxidative stress produced by marijuana smokers. An adverse effect enhanced by cannabinoids. American Journal of Respiratory Cell and Molecular Biology. 1999. 20(6):1286-93.
Tashkin, D. et al. Respiratory and immune consequences of marijuana smoking. Journal of Clinical Pharmacology. 2002. 42(11 Suppl):71S-81S.
