Smoke under fire

Smoking marijuana is no less harmful than smoking tobacco, according to a Canadian study of the toxic effects on cells. The conclusion was drawn from an examination of the cytotoxicity, mutagenicity and clastogenicity of mainstream and sidestream marijuana smoke as compared to tobacco smoke.

Marijuana use is on the rise and has garnered increasing media and medical attention because of the development of strains of the drug that have much higher concentrations of the active cannabinoid compounds. Moreover, there are tentative research results that suggests its use might help ameliorate the symptoms of diseases such as multiple sclerosis, although much of the evidence is anecdotal. Alongside this interest is the notion that marijuana is less harmful to health than tobacco smoke.

Marijuana is apparently viewed as a "natural" product and somehow by implication less harmful than manufactured tobacco products. Public attitudes towards marijuana are constantly changing. National restrictions in various countries on its use seem to toggle between allowing possession for personal or medicinal use as a "herbal remedy" and making it wholly illegal.

Now, Rebecca Maertens, Paul White, George Douglas, Pascale Bellier, James McNamee, Vidya Thuppal, and Mike Walker of the Research and Radiation Protection Directorate and Genevieve Levasseur and Suzanne Desjardins of the Tobacco and Drugs Directorate at Health Canada, in Ottawa, and William Rickert of Labstat International Inc, in Kitchener, Ontario, Canada, reveal new evidence of the potential dangers of marijuana smoke in the August 17 issue of the journal Chemical Research in Toxicology.

The researchers have demonstrated that smoking marijuana, just as with smoking tobacco, has serious toxic effects on cells. "To date, neither marijuana plant extracts nor delta-9-tetrahydrocannabinol (THC), the main psychoactive component of marijuana, have been confirmed to be mutagenic or carcinogenic on their own," the team points out.

One of the problems with obtaining a definitive answer regarding the health effects of marijuana smoke lies in the fact that it is very difficult to find subjects for clinical studies who have smoked only marijuana and avoided tobacco. Marijuana smoke certainly has adverse effects on the lungs. Pinning down its potential to cause lung cancer may, however, hinge on cytotoxicity studies that reveal a detailed mechanism by which this type of smoke could trigger carcinogenic biochemistry.

In this new study, Maertens and colleagues have begun to address the question by comparing marijuana smoke with tobacco smoke in terms of direct cytotoxicity and damage to DNA. The team exposed cultured animal cells and bacteria to condensed smoke samples from either marijuana or tobacco. They then carried out several assays, including Salmonella mutagenicity, and ability to induce chromosomal damage (i.e., micronucleus formation), and used statistical methods to determine the significance of the concentration effect.

The team adds that, "it is generally acknowledged that, like tobacco, marijuana smoke contains harmful substances that likely stem from the pyrolysis of the plant material (i.e., the smoking process)." In an earlier study they carried out a systematic comparison of the chemical composition of mainstream and sidestream marijuana and tobacco smoke from cigarettes and joints prepared under the same conditions. "That work confirmed that marijuana smoke condensates contain qualitatively the same chemicals as tobacco smoke," the team explains.

This should be a cause for concern for marijuana users, given that tobacco smoke has been associated with various detrimental effects on the lung, including chronic bronchitis, oedema, and excess mucus secretion. Moreover, given that of the thousands of compounds identified in tobacco smoke, more than 80 have been classified as carcinogenic by the International Agency for Research on Cancer (IARC) there could be direct correlation between marijuana smoking and lung cancer risk, just as there is with smoking tobacco.

Ultimately, the team's results suggest that marijuana smoke causes more damage to cells and DNA than tobacco smoke. However, tobacco smoke apparently causes chromosomal damage that marijuana smoke does not.