Cannabis a Greater Cancer Risk Than Tobacco

Cannabis cigarette smoke contains twice the level of carcinogens as that in tobacco cigarettes, making smoking a cannabis cigarette equivalent to 20 ordinary cigarettes in terms of lung cancer risk, a new study warns.

Researchers at the Medical Research Institute of New Zealand (MRINZ, Wellington), interviewed lung cancer patients selected from the New Zealand cancer registry and hospital databases. In total, 79 cases of lung cancer and 324 controls randomly selected from the electoral roll were included in the study. Interviewer-administered questionnaires were used to assess possible risk factors, including cannabis use, smoking, family history, alcohol consumption, and occupation. The relative risk of lung cancer associated with cannabis smoking was estimated by logistic regression.

The researchers found that the risk of lung cancer increased by 8% for each daily cannabis-cigarette per year of cannabis smoking (after adjustment for confounding variables including cigarette smoking), and 7% for each tobacco-pack per year of cigarette smoking (after adjustment for confounding variables including cannabis smoking). In total, lung cancer risk rose by 5.7 times for patients who smoked more than one cannabis cigarette a day for 10 years, or two cannabis cigarettes a day for 5 years, after adjusting for other variables, including cigarette smoking. The researchers added that cannabis smoke contains twice the level of carcinogens, such as polyaromatic hydrocarbons, when compared with tobacco cigarettes. The method of smoking also increases the risk, since cannabis cigarettes are typically smoked without a proper filter and almost to the very tip, which increases the amount of smoke inhaled. The cannabis smoker inhales more deeply and for longer, facilitating the deposition of carcinogens in the airways, and elevating carbon monoxide levels in the bloodstream by a factor of five. The study was published in the February 2008 issue of the European Respiratory Journal.

Cannabis use could already be responsible for one in 20 lung cancers diagnosed in New Zealand, said lead author Professor Richard Beasley, M.D. In the near future we may see an 'epidemic' of lung cancers connected with this new carcinogen. And the future risk probably applies to many other countries, where increasing use of cannabis among young adults and adolescents is becoming a major public health problem.

Cannabis, also known as marijuana, ganja, or hashish is a psychoactive product of the plant Cannabis sativa. The main biologically active chemical compound in cannabis is delta-9-tetrahydrocannabinol, commonly referred to as THC.


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Medical Research Institute of New Zealand