Reply #79: Cannabis Smoke and Cancer: Assessing the Risk

[bemildred]

Presumptions regarding cannabis use as a risk factor for the development of certain types of cancer, particularly lung cancer, warrant critical examination. Epidemiologic studies over the past several decades have established causation between alcohol consumption and cancers of the oral cavity, pharynx, larynx, esophagus, liver, colon and rectum, among others. Tobacco use, particularly cigarette smoking, has also been determined to cause similar upper aerodigestive tract (UAT) cancers, as well as cancers of the pancreas, kidneys and bladder, and is implicated with cancers of the stomach and liver, among others.

To date, similar epidemiologic and/or clinical studies on the use of cannabis and cancer are few and not definitive. However, the public and policy-makers should interpret the ambiguity of these results with caution – neither construing them at this time as an endorsement of cannabis’ safety nor as an indictment of its potential health hazards.

---

Cannabis smoke contains many of the same carcinogens as tobacco smoke, including greater concentrations of certain aromatic hydrocarbons such as benzopyrene, prompting fears that chronic marijuana inhalation may be a risk factor for tobacco-use related cancers. However, marijuana smoke also contains cannabinoids such as THC (delta-9-tetrahydrocannabinol) and CBD (cannabidiol), which are non-carcinogenic and demonstrate anti-cancer properties in vivo and in vitro. By contrast, nicotine promotes the development of cancer cells and their blood supply. In addition, cannabinoids stimulate other biological activities and responses that may mitigate the carcinogenic effects of smoke, such as down-regulating the inflammatory arm of the immune system that is responsible for producing potentially carcinogenic free radicals (unstable atoms that are believed to accelerate the progression of cancer).

Cannabis smoke – unlike tobacco smoke – has not been definitively linked to cancer in humans, including those cancers associated with tobacco use. However, certain cellular abnormalities in the lungs have been identified more frequently in long-term smokers of cannabis compared to non-smokers. Chronic exposure to cannabis smoke has also been associated with the development of pre-cancerous changes in bronchial and epithelium cells in similar rates to tobacco smokers. Cellular abnormalities were most present in individuals who smoked both tobacco and marijuana, implying that cannabis and tobacco smoke may have an additive adverse effect on airway tissue. The results suggest that long-term exposure to cannabis smoke, particularly when combined with tobacco smoking, is capable of damaging the bronchial system in ways that could one day lead to respiratory cancers. However, to date, no epidemiologic studies of cannabis-only smokers have yet to reveal such a finding. Larger, better-controlled studies are warranted.

http://norml.org/index.cfm?Group_ID=6891