As public support for amending America’s antiquated and failed cannabis criminalization policies continues to grow to record levels, stalwart prohibitionists – predictably – are doubling down on tried-and-true propaganda tactics to attempt to turn the tide. One of their most common strategies is to emphasize alleged health risks associated with marijuana consumption, in particular the claim that cannabis smoking causes cancer and other tobacco-related respiratory risks.



A recent example of this argument appeared in an October 29, 2013 Seattle Post-Intelligencer commentary, entitled “Marijuana smoking and the risk of lung cancer” by Eric Vallieres of the Swedish Medical Center in Seattle, Washington. Predictably, his alarmist commentary is heavy on rhetoric but woefully short on facts.



Of course, no one argues that the ingestion of combustive smoke, whether it is tobacco smoke or cannabis smoke, is healthy. However, it is inaccurate to allege that the risks to the consumer posed by these two substances are equal. In fact, the most recently available peer-reviewed science clearly rebukes the allegation that cannabis is as equal to or more dangerous than tobacco. For example, writing in the prestigious Journal of the American Medical Association (JAMA) in 2012, researchers from the University of California, San Francisco reported that occasional to moderate cannabis consumption was not associated with the adversely pulmonary risks associated with tobacco smoking. Investigators "confirmed the expected reductions in FEV1 (forced expiratory volume in the first second of expiration) and FVC (forced vital capacity)" in tobacco smokers. By contrast, "Marijuana use was associated with higher FEV1 and FVC at the low levels of exposure typical for most marijuana users. With up to 7 joint-years of lifetime exposure (e.g., 1 joint/d for 7 years or 1 joint/wk for 49 years), we found no evidence that increasing exposure to marijuana adversely affects pulmonary function." The full study may be read online here.



The findings in JAMA were hardly a surprise. Previously, the largest case-controlled study ever to investigate the respiratory effects of marijuana smoking reported that cannabis use was not associated with lung-related cancers, even among subjects who reported smoking more than 22,000 joints over their lifetime. Summarizing the study’s findings in The Washington Post, lead investigator and pulmonologist Dr. Donald Tashkin of UCLA concluded, “"We hypothesized that there would be a positive association between marijuana use and lung cancer, and that the association would be more positive with heavier use. What we found instead was no association at all, and even a suggestion of some protective effect." The full study is available here. (Notably, pot propagandists such as Dr. Vallieres try to in vain to undermine these findings by citing a 2008 New Zealand study, which some purport to definitively demonstrate a link between cannabis use and lung cancer. In reality, that study only reported a positive correlation in 14 heavy using subjects – a sample size far too small to draw any conclusions from and a result that has, to date, never been replicated in any large-scale population case-control models. Moreover, the same study also found that light-to-moderate lifetime cannabis consumers, who consisted of the majority of the trials’ participants, possessed no increased risk of cancer.)



More recently, this past May presenters at the annual meeting of the American Academy for Cancer Research reported that subjects who regularly inhale cannabis smoke possess no greater risk of lung cancer than do those who consume it occasionally or not at all — according to an analysis of six case-control studies, conducted between 1999 and 2012, involving over 5,000 subjects (2,159 cases and 2,985 controls) from around the world. They concluded, "Our pooled results showed no significant association between the intensity, duration, or cumulative consumption of cannabis smoke and the risk of lung cancer overall or in never smokers."



Most recently, an editorial in July published in the journal Annals of the American Thoracic Society concluded: “Cannabis smoking is not equivalent to tobacco smoking in terms of respiratory risk. … [C]annabis smoking does not seem to increase risk of chronic obstructive pulmonary disease (COPD) or airway cancers. In fact, there is even a suggestion that at low doses cannabis may be protective for both conditions. … This conclusion will affect the way health professionals interact with patients, parents with teenagers, and policy makers with their constituents. … Efforts to develop cleaner cannabinoid delivery systems can and should continue, but at least for now, [those] who smoke small amounts of cannabis for medical or recreational purposes can breathe a little bit easier.”



Why have scientists not identified a cannabis smoke/cancer link? The answer may be because cannabis, unlike tobacco, contains anti-cancer causing agents – a fact most recently reaffirmed this week in Newsweek on October 29 under the headline “Marijuana might kill cancer.” Reports the story, “In a paper published in October’s Anticancer Research, Wai Liu, a senior research fellow at St. George’s University of London, reports that he found six cannabinoids – active components of the cannabis plant – that can slow or outright kill cancer cells.” Previous peer-reviewed assessments of the properties of cannabis smoke and tobacco smoke further acknowledge that the pharmacological activities of these substances differ in such a manner that they are by no means equally carcinogenic.



It is true that some studies of cannabis smoke and pulmonary function indicate that chronic exposure may be associated with an increased risk of certain respiratory complications, including cough, bronchitis, phlegm. That said, the ingestion of cannabis via alternative methods such as edibles, liquid tinctures, or via vaporization — a process whereby the plant’s cannabinoids are heated to the point of vaporization but below the point of combustion –- virtually eliminates consumers’ exposure to such unwanted risk factors and has been determined to be a ‘safe and effective’ method of ingestion in clinical trial settings.



Cannabis smoking is certainly not without potential risks. But these risks should not be overstated, nor should they be asserted as a justification for a public policy that continues to criminalize and stigmatize responsible, adult cannabis consumers.