Eight US states, the District of Columbia, and the country of Uruguay have recently legalized the recreational use of marijuana, with Canada and more US states poised to do the same. The new laws include limits on youth access, operation of motor vehicles when using, and high-volume purchases or possession. However, none of the laws consider which kinds of marijuana products should and should not be legally sold.

While we take no position on the overall desirability of marijuana legalization, we propose here that policy makers in favor of it consider only permitting the sale of tetrahydrocannabinol (THC) extracts intended for vaporization or eating, and prohibiting combustible marijuana product sales. While implemented laws allow growing of marijuana for personal use, the policy we propose here would prohibit only the sale of marijuana cigarettes and their makings—flowers, stems, and seeds—to discourage their commercialization and mass production.

Those crafting marijuana laws can draw upon lessons learned about the harms of combusted tobacco and the smoking control policies that followed. Given what we already know about the health hazards of combusted marijuana and the difficulty of controlling the sale of commercially established products, policy makers should capitalize on this opportunity to create a legal marijuana market that mitigates potentially significant harms associated with inhaling combusted marijuana while still facilitating desired benefits of recreational marijuana.

Diverging Trends: Recreational Marijuana Legalization Versus Increasing Restrictions On Tobacco Smoking

The trend toward marijuana liberalization has grown since the mid-1990s to most recently encompass recreational use. By 2018, more than 50 million Americans 21 or older will live in states with access to legal recreational marijuana. Proponents of legalization argue that it reduces the high social costs of criminal law enforcement, an ineffective deterrent to use, the burdens of which fall disproportionately on racial minorities. Creating a legal market for marijuana also facilitates taxes on sales, the revenue from which may be used for public benefit. Legalization, moreover, increases access to a drug less prone to dependence than alcohol or tobacco for therapeutic and pleasure-seeking purposes. Public support for legal marijuana access has risen three-fold in the United States since the 1970s to reach 60 percent in 2016. Likewise, in other countries such as New Zealand, Canada, and France, the majority of the public say they favor legalization of marijuana sales. As momentum to broaden marijuana access builds, policy maker focus ought to prioritize ways to reduce potential harms of marijuana products.

Alongside recreational marijuana use liberalization, policy interventions designed to limit tobacco smoking have proliferated, based on what we have learned about the harms of combusted tobacco—both for the user and those exposed second-hand. This apparent policy divergence from marijuana legalization presents an opportunity for those crafting marijuana policy to learn from the tobacco-smoking experience. After all, both products involve psycho-active substances that can be delivered to the bloodstream in multiple ways. Combustible marijuana likely poses similar risks to those of combustible tobacco, while vaporizing or eating marijuana products offers a “cleaner” delivery mechanism. Why repeat the devastating public health harms of smoking tobacco when policy makers can reasonably mitigate similar consequences of smoking marijuana?

Health Concerns Around Marijuana Combustion

Among the chief concerns with marijuana use, although not yet reflected in liberalization policies, are health harms associated with combustion. Combustion of any substance produces hundreds of chemical compounds, including many known toxins. In a recent comprehensive review of the scientific literature, the National Academies of Sciences, Engineering, and Medicine concluded that “smoked marijuana…is a crude THC delivery system that also delivers harmful substances.” The report and other reviews found strong evidence linking combusted marijuana to increased risk for chronic bronchitis.

Emerging studies link marijuana smoking to increased risk of cardiovascular mortality. Evidence identifying marijuana smoking as a risk factor for lung cancer is not as robust, although potential harms cannot be ruled out, particularly because marijuana smoke is carcinogenic. Research on harms from second-hand marijuana smoke is lacking, but analogizing from tobacco, it is reasonable to assume that chemicals and particulate matter released in marijuana smoke would be harmful to bystanders. Although a typical tobacco user smokes more often than a typical marijuana user, the relative harm of marijuana combustion may not be substantially lower than that for tobacco because some toxins released are higher per unit in a marijuana versus a tobacco cigarette.

Several factors undermine the existing evidence base on health outcomes associated with marijuana use, emphasizing the need to prioritize research in this area alongside policy development. The listing of marijuana as a Schedule I drug by the federal Drug Enforcement Agency has hampered funding and execution of studies of its therapeutic benefits and harms. Additionally, evidence related to the harms of marijuana use generally comes from studies of lower-potency products (that is, with lower THC content) than are marketed today and can be anticipated in the future. Therefore, it is possible that the harms associated with combustion may differ from those reflected in the current literature.

Potential harms of combusted marijuana extend beyond marijuana alone. Combination marijuana and tobacco use, which can involve blending the substances into a single smoked product or smoking tobacco and marijuana separately but in close temporal proximity, is prevalent. Limiting the availability of combustible marijuana may reduce the amount of dual product use, thereby reducing the amount of and hazards associated with tobacco smoking.

Shifting To Vaporized And Edible Marijuana

Edible and vaporized marijuana products offer the potential to deliver therapeutic and euphoric benefits of marijuana while avoiding cardiopulmonary-related harms of combustion. Although precise estimates of the decreased risks associated with this substitution are not available, by analogy the health risks for smokeless and vaporized tobacco products are estimated to be roughly 90 percent less than those of combusted tobacco.

Valid concerns have been raised about the potential health harms from commercially marketed edibles, especially their attractiveness to, accessibility by, and increasing exposure and overdoses among children. We strongly support prohibitions on the sale of marijuana products—including edibles—to minors, clearly labeling product THC content and requiring child-proof packaging. Additionally, if marijuana is only legally available for sale in forms that do not resemble cigarettes, children may be less likely to cross over between products.

Combusting marijuana is an entrenched behavior that may be challenging to modify. Many marijuana users exhibit a preference for smoking, the primary delivery mode for the drug, and may be less satisfied if combustible products cannot be purchased. However, smoking marijuana is not yet as established in legal markets as is smoking tobacco, and newer users could vape or consume edibles instead of developing preferences for combustion. A subset of established marijuana smokers likely will opt for readily available non-combustibles, particularly when educated about the risks associated with combustion and as social preferences change over time. As well, vaping may serve as a harm-reduction strategy that mimics the individual behavior, social aspects, and psychotropic effects of smoking, and is found to be just as satisfying. Finally, extracted THC for sale as oils, waxes, and edibles is amenable to mass production to a greater degree than raw-form combustible marijuana, potentially facilitating lower prices and a shift toward consumption of these products post-legalization. Combatting and policing a black market for combustible marijuana would still be required, although regulatory enforcement would be limited to retail establishments instead of personal use.

Designing A Safer Marijuana Market From The Outset

Imagine that tobacco had been illegal for most of the 20th century, and its legalization were being considered today—and that we possessed our current knowledge about the health consequences of smoking tobacco. Few would advocate for its legal availability in combustible form, given that alternative available delivery modes—e-cigarettes and smokeless tobacco—can deliver the same psycho-active drug, nicotine, in forms far less likely to cause serious disease.

While we do not have the chance to design a legal nicotine market from scratch, our body politic has the opportunity to design the legal market for marijuana from the ground up. The legalization of recreational marijuana sales has thus far included all forms or only combustible forms (as in the case of Uruguay) of marijuana. Product availability in these new legal markets seems to have been guided by economic considerations and voter preferences, instead of measured consideration prior to legalization of the relative risks and harms of different types of marijuana products.

Policy makers in jurisdictions considering legalization are not bound by custom to make available all forms of marijuana for recreational use. Little prior interstate commerce of legal marijuana products exists, and most states have yet to legalize recreational use. The environment is ripe to experiment with different types of markets, and entrepreneurial policy makers could embark on implementing a safer legal marijuana market that omits combustibles, based on our current and developing knowledge.

Action In The Face Of Some Uncertainty

Marijuana policy makers would be wise to draw upon lessons learned from the experience with tobacco. In the tobacco policy realm, there is a broad consensus that it would be difficult to design a consumer product more harmful than a combustible cigarette—the product that kills one in two long-term users. The suspicion that cigarettes were a dangerous product was well-founded early in the 20th century in animal model studies and pioneering epidemiological surveys. While not risk-free, smokeless tobacco and e-cigarettes will not kill nearly so many of their users. Unfortunately, cigarettes are entrenched within the tobacco marketplace. A protracted battle has raged between public health on the one side, which would benefit by shifting nicotine consumption to safer products or eliminating nicotine use altogether, and incumbent commercial interests and established consumer preferences on the other, which favor selling the most dangerous product, with neither side declaring decisive victory.

While uncertainty still exists regarding the relative harms of different marijuana products and robust research is warranted, waiting for perfect scientific consensus about the scope and nature of harms related to marijuana combustion is unwise. The evidence base around marijuana combustion harms is already strong, and growing. Arriving at total consensus will take decades—as it took to link cigarettes to lung cancer—and waiting to embark on an alternative, very likely safer policy regime has real costs, measured in disease and death. Permitting the sale of THC extracts for consumption in edible or vaporized form will neither compromise therapeutic nor euphoric benefits of recreational marijuana use. In addition, creating variation in recreational marijuana policy regimes—between those already enacted that permit marijuana combustion and those enacted in the future that don’t—would create natural experiments ripe to study the differential effects and quantify harms versus benefits. Policy makers in favor of legalization should seize the opportunity to design a new market that permits recreational sale of marijuana only in edible or vaporized form, to minimize the potential for the kind of disease burden associated with smoked tobacco.

Authors’ Note

We thank Daniel J. Clauw, Mark A. R. Kleiman, and Lynn T. Kozlowski, for their valuable insights.