a discussion of the potential harms of inhaling cannabis smoke (1). In spite of the intuitive position that âsmoking is bad,â estimates of the level of risk of cannabis ...
EDITORIALS Cannabis and the Lung: No More Smoking Gun? Smoking is the most common means of cannabis selfadministration for both medical and recreational purposes, and any consideration of the health effects of cannabis inevitably involves a discussion of the potential harms of inhaling cannabis smoke (1). In spite of the intuitive position that “smoking is bad,” estimates of the level of risk of cannabis smoking on the lung have been controversial and difficult to quantify or to interpret (2). In this issue of AnnalsATS (pp. 239–247), Professor Donald Tashkin presents the most comprehensive and authoritative review of the subject ever published (3). Tashkin knows of what he speaks; he has spent an entire career exploring the potential harms of cannabis smoking from the cellular to the epidemiological level. What can we learn from his timely review? Cannabis smoking is not equivalent to tobacco smoking in terms of respiratory risk. Despite the presence in cannabis smoke of known carcinogens, toxic gases, and particulates, cannabis 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 smoking may be protective for both conditions. These findings are inconsistent with the “smoking is bad” position. How, then, are we to handle these conclusions from the most authoritative voice on the subject? The message emerging from this paper is that smoking cannabis, particularly in low doses, is not as harmful as tobacco in terms of effects on the lung. This does not mean that cannabis smoking is not harmful; elevated rates of symptoms of chronic bronchitis are associated with cannabis smoking (4), and efforts to find alternatives to smoking should continue. Indeed, vaporization of cannabinoids has already been shown to mimic the pharmacokinetics of cannabis smoking while reducing exposure to toxic cannabis smoke ingredients such as carbon monoxide (5). This approach has recently been shown to be effective in clinical trials (6). Epidemiological studies have demonstrated an association between smoking cannabis for medical purposes and tobacco smoking (7, 8). If cannabis is to be used to improve health, then concomitant tobacco use should be strongly discouraged. From the standpoint of the use of cannabis for medical purposes, smoking is a “dirty” delivery system, albeit effective (9), and further monitoring of patients choosing this approach is strongly advised. The increasing number of U.S. states in which medical cannabis programs are in place, as well as those where cannabis has been legalized, offer a unique opportunity to monitor the respiratory health of subjects who choose to smoke cannabis as their method of cannabinoid delivery. These opportunities should not be missed. We are embarking on a massive social experiment, with different levels of legal cannabis use being permitted on a wide scale for the first time in over 80 years, and only conscientious pharmacovigilance will identify hitherto unknown adverse health effects. A consensus from the pulmonology community on how best to monitor the respiratory health of people using cannabis (for medical or recreational purposes) would be a welcome addition to the public health recommendations in jurisdictions where cannabis may be legally used. A few points regarding recent developments in cannabis policy are worth noting to put Tashkin’s review in historical context. Until recently, the process of societal and scientific “rediscovery” of cannabis has taken place exclusively within a climate of prohibition. 248
The “war on drugs” has created the entrenched and often militant positions of both cannabis activists and prohibitionists. Patients who discovered the medical properties of herbal cannabis along the way have effectively become the collateral damage in this war. Epidemiologic data collected in the past must be considered to be susceptible to a “prohibition” bias in which subjects may lie about cannabis use to avoid risking admission to an illegal activity; the magnitude and direction of this bias has never been evaluated. But the times, as the old song goes, are a-changing. Cannabis is approved for medical use in Israel, Canada, The Netherlands, and in 18 U.S. states. Cannabis is decriminalized for personal use in several European countries and is legalized in two U.S. states. These evolving attitudes create opportunities to examine the health effects of cannabis under a new paradigm of public health. The impact of cannabis use on mental health, traffic accidents, and health care utilization, as well as symptoms and disease outcomes, functionality, and quality of life, can now be addressed in a more open and objective manner. Concerns about the lung are paramount when the drug in question is largely smoked, but Tashkin reassures us that the “accumulated weight of evidence” suggests that cannabis smoking is not a major risk factor for COPD and airway cancer. 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, patients who smoke small amounts of cannabis for medical or recreational purposes can breathe a little bit easier. Author disclosures are available with the text of this article at www.atsjournals.org. Mark A. Ware, M.D., M.R.C.P., M.Sc. Alan Edwards Pain Management Unit McGill University Health Centre Montreal, Quebec, Canada
References 1 Hall W, Degenhardt L. Adverse health effects of non-medical cannabis use. Lancet 2009;374:1383–1391. 2 Kalant H. Smoked marijuana as medicine: not much future. Clin Pharmacol Ther 2008;83:517–519. 3 Tashkin DP. Effects of marijuana smoking on the lung. Ann Am Thorac Soc 2013;10:239–247. 4 Aldington S, Williams M, Nowitz M, Weatherall M, Pritchard A, McNaughton A, Robinson G, Beasley R. Effects of cannabis on pulmonary structure, function and symptoms. Thorax 2007;62:1058–1063. 5 Abrams DI, Vizoso HP, Shade SB, Jay C, Kelly ME, Benowitz NL. Vaporization as a smokeless cannabis delivery system: a pilot study. Clin Pharmacol Ther 2007;82:572–578. 6 Wilsey B, Marcotte T, Deutsch R, Gouaux B, Sakai S, Donaghe H. Lowdose vaporized cannabis significantly improves neuropathic pain. J Pain 2013;14:136–148. 7 Clark AJ, Ware MA, Yazer E, Murray TJ, Lynch ME. Patterns of cannabis use among patients with multiple sclerosis. Neurology 2004;62:2098– 2100. 8 Ware MA, Doyle CR, Woods R, Lynch ME, Clark AJ. Cannabis use for chronic non-cancer pain: results of a prospective survey. Pain 2003; 102:211–216. 9 Wilsey B, Marcotte T, Tsodikov A, Millman J, Bentley H, Gouaux B, Fishman S. A randomized, placebo-controlled, crossover trial of cannabis cigarettes in neuropathic pain. J Pain 2008;9:506–521. Copyright © 2013 by the American Thoracic Society
AnnalsATS Volume 10 Number 3 | June 2013
