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Electronic cigarettes (ECIGs) are a class of products that use an electrically powered heating element to aerosolise a liquid for user inhalation. One subgroup of the class, ‘closed-system’ ECIGs, is sold ready-to-use and is constructed of component parts that cannot be modified readily and are filled with liquids that cannot be accessed easily. Another subgroup of the class, ‘open-system’ ECIGs, allows the user to modify virtually every component part and/or fill them with any liquid. Thus, although any given closed-system ECIG can be considered a single product, any given open-system ECIG must be considered to be a nearly infinite number of products, as the user controls the system’s electrical power, heating element characteristics and liquid constituents, which almost always include solvents like propylene glycol and vegetable glycerin, sweeteners and flavourants, and at least one psychoactive drug such as nicotine or tetrahydrocannabinol. This user control is important because every aspect of ECIGs listed above—device power, heating element, liquid constituents—can influence the rate of toxicant (drug and non-drug) delivery to the user and thus user health. In part, because ECIGs deliver dependence-producing, psychoactive drugs and also because of concerns and increasing evidence that the aerosols that they emit are harmful, a variety of countries have acted to protect public health by banning the product class entirely (eg, Brazil, India and Uruguay) or regulating ECIG sales, marketing or use (eg, Canada, European Union, England, New Zealand and Philippines). Note that in no country are ECIGs approved as a therapeutic product. The goal of this commentary is to suggest that the current level of heterogeneity seen in open-system ECIGs is incompatible with effective regulation. To achieve this goal, we consider three potential ECIG regulations—reducing the availability of flavoured ECIG liquids, limiting liquid nicotine content and constraining nicotine emissions—and demonstrate that, in the context of open-system ECIGs, enforcing these regulations is virtually impossible.
Flavour regulation cannot be successful with open-system ECIGs
Recent concerns over the increase in ECIG use among youth have led some policy-makers to suggest reducing the availability of flavoured ECIG liquids. However, in a context where open-system ECIG liquid reservoirs (ie, tanks, cartridges and refillable pods) are made to be filled by the user, these potential regulations are unlikely to succeed. That is, in the open-system context, a user can purchase a legal and regulated unflavoured nicotine liquid and then add to it a flavoured liquid that does not contain nicotine. One strategy, already in use, is to sell flavoured nicotine-free liquids alongside the flavourless nicotine liquid.1 Another strategy that has been used by ECIG users for several years2 3 is to mix flavoured nicotine liquids at home: do-it-yourself (DIY) flavour-mixing recipes are available online (eg,4 along with detailed instructions).5 The existence of DIY flavour mixing also suggests unintended consequences of flavour regulation in the open-system context. That is, reducing flavour availability may drive more users to mix their own liquids, risking toxic effects if nicotine is handled unsafely or if users are unaware that some flavourants that are safe to eat can be dangerous when heated and inhaled (eg, some sweeteners that produce toxic furans when heated).6 A context in which open-system ECIG users can buy unflavoured nicotine liquid and add to it any flavourant they buy or make at home is not compatible with effective flavour regulation: flavoured ECIG liquids will still exist, will be unregulated and may increase the dangers of ECIG use.
Limits on liquid ECIG nicotine content cannot achieve intended goals with open-system ECIGs
Some jurisdictions have already placed limits on ECIG nicotine content,7 and others are considering following suit.8 The European Union’s Tobacco Products Directive limits ECIG liquids to no >20 mg/mL nicotine to allow ‘for a delivery of nicotine that is comparable to the permitted dose of nicotine derived from a standard cigarette…’.7 The intended goal of this directive is clear: limiting liquid concentration to no >20 mg/mL is supposed to limit nicotine delivery to the user such that delivery does not exceed that of a tobacco cigarette. However, the directive does not account for heterogeneity in open-system product characteristics that work against its intent and, in fact, may increase public health risk. Specifically, open systems often have modifiable power settings (measured in watts, W) that can influence ECIG nicotine emissions such that increasing wattage increases nicotine yield9 10: early ECIG models were powered at ≤10 W, but some models available today can achieve ≥200 W.11 Recent data demonstrate that 10 puffs from high power ECIGs (mean=70 W) filled with only 4 mg/mL nicotine liquid (on average) can attain and sometimes exceed the nicotine delivery of a tobacco cigarette.12 These data illustrate that when a liquid contains <20 mg/mL nicotine (and is thus compliant with the European Union directive) and is aerosolised in a high wattage device (eg, 70 W), the combination can produce a nicotine delivery profile that exceeds that of a combustible cigarette and is therefore contrary to the intent of the directive. These higher-power devices deliver nicotine so effectively by aerosolising much more liquid/puff, relative to lower-power devices.10 For users who move from low-power devices to high-power devices, exposure to more aerosol per puff may increase the risk to their health because they are exposed to much greater amounts of nicotine (thus potentially increasing their own nicotine dependence) and also any non-nicotine toxicants.
Constraining the rate of ECIG nicotine and other toxicant emissions cannot occur with open-system ECIGs
One response to the heterogeneity of ECIGs as a product class is for regulators to focus less on product characteristics and more on product performance. For example, rather than limiting liquid nicotine content, regulators might limit ECIG nicotine emissions. One such performance standard involves regulating the rate at which an ECIG emits nicotine: its nicotine ‘flux’.13 14 There are at least three advantages to nicotine flux as a regulatory target. First, the rate of drug delivery is a key aspect of the extent to which a drug will be abused,15 and nicotine flux describes the rate at which an ECIG delivers nicotine to the user. If the goal of regulation is to decrease the likelihood that ECIGs will be abused by a population (ie, non-smoking youth), decreasing ECIG nicotine flux may be an effective way to achieve this goal. Second, a given ECIG’s nicotine flux is a result of all aspects of that ECIG’s characteristics (eg, construction, wattage and liquid nicotine content) so regulators need not try to focus simultaneously on myriad targets that can evolve over time. Rather, they focus on a product performance target—a range of nicotine emission rates—and manufacturers can choose whatever device/liquid characteristics that they can prove fall within that target performance range safely. Note that the flux target need not be a single value, but rather a range of allowable nicotine flux conditions (ie, a nicotine emission rate no less than X and no greater than Y), thus allowing for a range of closed-system products. Third, a mathematical model can be used to predict the nicotine flux of any ECIG.10 Thus, regulators have at their disposal a tool that allows them to examine efficiently an array of products to determine if those products meet or fall outside of a specified nicotine flux range. Overall, a performance standard like nicotine flux has clear advantages over multiple product standards. However, as with restricting flavour availability and limiting nicotine content, flux regulation, whatever its advantages, fails in an open-system context where users are able to modify devices and liquids easily.
Conclusions
Open-system ECIGs cannot be regulated effectively: they have too many user-accessible, policy-defeating features. Therefore, policy-makers interested in regulating ECIGs should not authorise for marketing any ECIG product that allows user access to and modification of these policy-defeating features. One objection to this idea might be that producing closed-system ECIGs is not feasible. This objection ignores the evidence: there is already a closed system on the global market (JUUL) and, for good or ill, its popularity is growing.16 Not surprisingly, a closed system like this one is much easier to regulate than the extant open systems with which it competes. The battery can be accessed only by destroying the device casing, therefore increasing voltage is difficult. The heating element cannot be replaced as it is integrated into a ‘pod’ that contains the liquid, so decreasing resistance is impossible. The liquid is difficult to access, meaning that altering the flavour or other liquid characteristics is challenging (and regulation could make it more so). Regulations aimed at decreasing the flavour availability and nicotine flux of closed systems can be effective. However, for open systems that are available to consumers worldwide, regulations that effectively limit ECIG flavour availability or nicotine emissions are illusory.
Footnotes
Collaborators CSTP Nicotine Flux Work Group: Andrew J Barnes, Alison Breland, Caroline O Cobb, Joanna E Cohen, Rachel El Hage, Ahmad El Hellani, Alisha Eversole, Jeffrey J Hardesty, Nathalie Hayeck, Cosima Hoetger, Ebrahim Karam, Sarah F Maloney, Alyssa K Rudy, Najat Aoun Saliba, Rola Salman, Soha Talih, Theodore Wagener.
Contributors The idea for this commentary was developed at a meeting of the CSTP Nicotine Flux Work Group in Lisbon, Portugal, 25–27 October 2019, thus all CSTP Nicotine Flux Work Group members are listed as Collaborators and the work group name is included in the author list. The first draft of the manuscript was prepared by TE, and finalised with input from EKS and AS.
Funding This work was supported by the National Institute on Drug Abuse of the US National Institutes of Health (NIH) under Award Number U54DA036105 and the Center for Tobacco Products of the U.S. Food and Drug Administration (FDA).
Competing interests TE and AS are paid consultants in litigation against the tobacco industry and are named on a patent for a device that measures the puffing behavior of electronic cigarette users. In addition, TE is a consultant in litigation against the electronic cigarette industry.
Patient consent for publication Not required.
Provenance and peer review Not commissioned; externally peer reviewed.