Annotated version of National Affairs article
In 2014, the Oxford English Dictionary christened “vape” the Word of the Year. The designation was a tribute to the impressive rise of the electronic cigarette, a battery-powered device that heats a flavored solution containing nicotine and converts it into an inhalable, or “vape-able,” aerosol. By the close of 2013, six years after e-cigarettes became available in the United States, sales had surpassed $1 billion, prompting financial analysts to proclaim them a threat to cigarette sales. Observers hailed e-cigarettes as “one of the most significant public-health innovations of modern times” and a “disruptive technology” poised to “revolutionize” public health. Invented for smokers who cannot or will not quit, e-cigarettes do not burn tobacco, and therefore emit a mere fraction of the carcinogens and hazardous gases than do conventional cigarettes. This means vaping is substantially less harmful than smoking, which causes roughly 480,000 American deaths each year. Today, roughly 11 million adults use electronic cigarettes. With the exception of quitting cold-turkey, vaping is not only the most popular strategy but the most effective. In other welcome news, early fears that e-cigarettes would “re-normalize” smoking among adults and lead teens to take up smoking have not materialized. And if over the next 10 years the nation’s smokers switched to vaping, according to conservative demographic estimates, more than 1.6 million premature deaths could be averted by 2100. In short, e-cigarettes offered a potent alternative to cigarettes, which Stanford historian of science Robert Procter has aptly called “the deadliest artifact in the history of human civilization.” Just five years later, in November 2019, several hundred vapers assembled on the White House ellipse. Pink clouds redolent of strawberry, cinnamon, and peach hung low in the air. “We vape, we vote,” the vapers chanted. “Flavors Save Lives” read their placards. The messages were aimed at President Trump who had announced weeks earlier that he planned to ban e-cigarette flavors. His move was just a part of a larger cultural and political campaign against vaping that shifted into high gear last fall. The drive included Congressional hearings with titles like “E-cigarettes: A Threat to Public Health.” Angry parents marched in protest. The American Medical Association urged a flat-out ban on vaping. A smokers’ helpline run out of a California state university launched a “quit vaping” program. Meanwhile, the market value of tobacco companies—which had declined by roughly half since around 2017—started to rebound, likely due to confidence that vaping would not be a serious long-term competitor with the more lucrative combustible cigarette. In a mere half a decade, the e-cigarette went from being lauded as a possible salvation from smoking to being denounced as a public-health disaster. How did this happen? How could local public-health officials in some cities facilitate their removal from store shelves while leaving deadly Marlboros and Newports for sale, waiting to fill the nicotine void? The answer involves some of the usual culprits—tone-deaf marketing by manufacturers, flawed regulation by government, and scare-mongering by politicians, and the media.  But something more troubling lies at the heart of the story: an extraordinary lack of intellectual integrity in a prominent sector of the public-health community.
From Hon Lik to JUUL
A Chinese pharmacist named Hon Lik invented the first commercially successful e-cigarette, spurred by his own difficulty quitting cigarettes and by his father’s lung cancer, which followed a lifetime of smoking. Hon’s disposable device looked like a metallic cigarette, featuring a red light at the end that glowed when a puff was drawn. He named his company Ruyan, meaning “almost smoke.” The disposable, pre-filled devices were brought to market in Beijing in 2003 and appeared in U.S. retail outlets in 2007. Domestic versions of these “first generation” e-cigarettes, also called cig-alikes, soon followed. The devices did not appeal to heavy smokers, however, because they delivered a weak dose of nicotine. A second-generation e-cigarette with increased battery power quickly emerged. Users pressed a button on a non-disposable pen-like apparatus to heat the nicotine solution and inhale the aerosol. Soon, a third generation of devices (“mods”) with even more powerful batteries came on the scene. Users’ signatures are the large, billowy clouds of vapor they blow. The palm-held devices have a mouthpiece containing the heating coil and a small receptacle, or “tank,” for e-liquid attached to a squarish body housing the rechargeable batteries. Second- and third-generation devices are called “open systems” because the user refills the tank. Vapers can mix their own e-liquids using a variety of flavors and strengths of nicotine. Enthusiasts customized batteries and coils in their own garages and workshops, and eventually opened vape shops and lounges. They posted instructional YouTube videos for vapers who wanted to modify their own apparatuses. The industry grew from the bottom-up, propelled by consumers’ word of mouth, as the vape shop became the center of vape culture. The typical owner is a former smoker who swears he owes his life to vaping and wants other smokers to convert. Proprietors help customers choose the devices, nicotine content, and flavors best for them. As one observer put it, vape shops are nothing less than “smoking cessation clinics.” Another described the shop and vape lounge “as a kind of neighborhood bar, with each new customer, there was a familiar greeting, an exchange of pleasantries, and the sense that it was one big smoky, weird-but-not-unpleasant-smelling family, united in the fact that they’d all quit cigarettes and now fear future government regulations would destroy their newfound habit and hobby.” Vaping has become an identity, complete with its own festivals; the first Vapefest took place in Fredricksburg, Virginia, in 2010. The fourth generation e-cigarette arrived in 2015, most notably in the form of JUUL, made by a company of the same name. The device resembles a sleek, four-inch thumb drive, and its battery can be recharged by plugging it into any USB port. JUUL uses a “pod-based” system; its e-liquid comes in small, sealed, replaceable units. A pack-a-day smoker trying to quit cigarettes would consume about a pod per day, as each JUUL puff is roughly equivalent to or slightly less than a cigarette puff. Originally available in eight flavors, including mango and cucumber, JUUL delivers a strong hit of nicotine to the brain and a punch to the back of the throat that smokers find particularly satisfying. JUUL comes closest to separating nicotine, a fairly benign substance, from the dangers of a delivery system (the cigarette) in a manner that many smokers find attractive. Sales rocketed six-fold to $1.3 billion from 2017 to 2018. Meanwhile, JUUL copycats began flooding the market in 2017. All four generations of e-cigarette have been inspired by the philosophy of “harm reduction,” which is the imperative to minimize hazard in people who, rather than desist, will continue to engage in risky behaviors. The virtue of vaping is that it uncouples deadly smoke from nicotine, which, contrary to common impression, has no appreciable role in causing cancer. Classic harm-reduction strategies include the distribution of condoms to teens and clean needles to injection-drug users, and pre-exposure prophylactic medication and safe-sex information for populations at risk for HIV/AIDS. As a safer alternative for smokers, vaping is to nicotine addicts what methadone is to opioid addicts. Many smokers find vaping more appealing than traditional nicotine gums and patches because of its cigarette-like attributes, such as the ritualistic handling of an object, the social dimension of use, the physical sensation of inhalation, and the “hit” of nicotine that it delivers. Yet many of the same public-health institutions that promote harm-reduction strategies to users of other drugs, are reluctant, if not hostile, to extending the same forbearance to smokers. This paradox is rooted in the anti-tobacco movement, which has, along with irresponsible actions by public-health institutions, derailed the vaping revolution.
Roots of Resistance
In the late 1970s, the tobacco-control movement began to coalesce. At its core were the American Cancer Society, the American Heart Association, and the American Lung Association. Soon 20 or so additional public-health groups would join, creating a heterogeneous group comprising physicians and epidemiologists, who were concerned with medical issues; social scientists and psychologists, who sought to modify smoking behavior; and the activists and scholar-activists, who devised policies and lobbied for them. Throughout the 1980s and ’90s the movement worked with state governments and Congress to raise cigarette excise taxes, adopt clean indoor air laws, strengthen warning labels, and impose marketing restrictions. To stop deceptive advertising and to establish oversight over the tobacco industry, the coalition fought to bring tobacco under the purview of the Food and Drug Administration. The search for a “safer” cigarette would become another target for the movement. The evolution of that search goes back to the 1950s, when news of the discovery of a tight link between smoking and lung cancer began appearing the popular literature. In 1952, Reader’s Digest published an expose titled “Cancer by the Carton.” Twelve years later, the landmark 1964 Surgeon General’s report identified smoking as a cause of lung cancer and heart disease. Tobacco companies responded to growing concerns about the health impact of smoking by developing filtered “light” brands with lower tar—the culprit in causing disease—and lower nicotine. Public-health authorities at the time encouraged their use, and in 1968, the National Cancer Institute began research to help develop a safer cigarette. Unfortunately, the “tar-reducing” methods employed by cigarette makers did not make them safer. The much-touted filters intended to trap tar also captured nicotine, making filtered products less satisfying and causing smokers to compensate by taking more puffs, longer puffs, or more vigorous puffs (inhaling more deeply) to get their preferred dose of nicotine. The ventilation holes in the filter, which were intended to introduce air and thereby dilute the smoke released, were defeated when smokers, wanting more nicotine and better taste, reflexively covered the holes with their fingers. This “fooled” the Federal Trade Commission’s smoking machines—meant to determine tar and nicotine yields—into measuring less tar and nicotine for a given puffing regime. Health advocates advised smokers not to alter their manner of smoking because smokers who took in less tar did indeed lower their risk of lung cancer. Cigarette manufacturers knew this too, yet issued no guidance against altering smoking patterns and continued to promote light cigarettes as less hazardous. By the 1980s, the tobacco-control movement felt betrayed by promises of “safer” products. The tobacco industry could not be trusted, a lesson subsequently reinforced by an infamous 1994 congressional hearing that further exposed their deception as top executives of seven major tobacco companies asserted, in tandem, that “nicotine is not addictive.” The next month, 4,000 pages of internal industry documents from a leading tobacco company, Brown and Williamson, spanning four decades were leaked by a mysterious “Mr. Butts” to a professor at the University of California at San Francisco. The contents were published in 1996 as The Cigarette Papers. They confirmed that the company had been aware of the cancerous effects of smoking for decades but continued to maintain that “causation has not been proved.” Activists were outraged, bent on destroying an industry that had spent millions trying to recruit new teen users while knowingly lying about the deadliness of its product. Thus, when e-cigarettes came to the market in 2007, tobacco controllers rebelled: They were hostile to the notion that a safer product was possible—the very term “harm reduction became synonymous with industry deception—and were distressed by the very optics. Not only did early e-cigarettes look like their combustible counterparts, users held them as they would cigarettes, and exhaled vapor that resembled smoke. Subsequent, more powerful versions of e-cigarettes enabled users to blow large plumes of vapor, magnifying the erroneous impression that vaping was just another form of smoking. Adding to the offense, in critics’ eyes, was that vaping devices delivered nicotine in a satisfying manner with enjoyable flavors. For years, vaping has been up against rigid attitudes of activists wishing to prohibit all tobacco products. When locked in combat with the cigarette industry, the movement was a relatively unified force. Science-driven researchers and agenda-driven activists shared the basic policy goal of eradicating all tobacco use and the diseases it caused. But the emergence of e-cigarettes exposed the movement’s latent fault lines. For the movement’s majority, reduced-risk products are still unacceptable; tobacco controllers have their sights on restricting—and ideally banning—tobacco in any form. Inhaled nicotine, so intimately connected with smoking, is regarded a proxy for cigarettes and needs to be abolished too, despite the long-proven clinical reality that nicotine is a relatively benign substance. They do accept nicotine in the form of gum, patches, sprays, inhalers, or lozenges, though, because these are medicinal forms of nicotine replacement and because they are not manufactured by the tobacco industry, as are some first and fourth generation e-cigarettes. The concepts of harm reduction and the possibility of safer products were otherwise dismissed out of hand by most in the movement. However, a smaller, more pragmatic faction conceded that vaping might have a role in weaning smokers off cigarettes, though only as a temporary method. Meanwhile, a minority—the harm-reductionists—embraced vaping as a long-term option for people who could not quit after trying other forms of nicotine, a view that threatened the movement’s rank and file. Harm-reductionists condemned the absolutist views and policies of tobacco controllers as tantamount to a “quit or die” message to smokers. These three camps—hardline tobacco controllers, vaping temporizers, and harm-reductionists—could never find a way to compromise. As Scott Ballin, former counsel to the American Heart Association and a 40-year veteran of tobacco policy observes, “Many are still fighting the old smoking wars of the ’80s and ’90s where enemy lines were clear: tobacco industry versus public health. Since then, a tribalism between factions has developed.” “Many saw in e-cigarettes a Trojan horse that would slow the process of smoking denormalization, reduce the number of people trying to quit, and seduce young nonsmokers,” wrote Amy Fairchild and colleagues in the New England Journal of Medicine in 2018. Given its innately precautionary orientation, the tobacco-control movement became fixated on e-cigarettes’ appeal to young people. Without question, minors’ welfare demands greater oversight than adults’ well-being—but not at the cost of clear-eyed perspective. Yet that was the price they were willing to pay. “Mainstream of public health is vehemently opposed to vaping, and focused tunnel-vision-like on kids and vaping,” according to Kenneth Warner professor and dean emeritus of the University of Michigan School of Public Health, while it is “ignoring the adult smokers who are quitting by vaping.” Such outsized fears of contaminating youth set the stage for moral panic. Eventually, the simmering disapproval of e-cigarettes rose to the surface, as three major developments gave rise in 2014 to a watershed moment in the short history of e-cigarettes. One was a publication from the Surgeon General’s office that tentatively recognized the potential of e-cigarettes to wean smokers off cigarettes. The second was the FDA’s call for comments on whether the agency should assume regulatory jurisdiction over e-cigarettes by “deeming” them to be tobacco products. The third was the reported tripling in youth vaping, including youthful experimentation involving a single puff, between 2013 and 2014. With the Surgeon General and the FDA taking e-cigarettes seriously, and with youth use rising, the opponents of vaping were galvanized to take bolder action.
Merchants of Doubt
C. Everett Koop, Surgeon General under President Ronald Reagan, was an ardent crusader against smoking. In the wake of the Surgeon General’s 1964 report, Koop said that he “frequently spoke of the sleazy behavior of the tobacco industry in its attempts to discredit legitimate science as part of its overall effort to create controversy and doubt [surrounding the relationship between smoking and lung cancer].” The word “doubt” carried singular meaning in tobacco-policy circles, having been used in an infamous 1969 memo circulated within Brown and Williamson Tobacco Company, the maker of Pall Mall. “Doubt is our product,” wrote a company executive, “it is the best means of competing with the ‘body of fact’ [and] establishing a controversy” surrounding the dangers of smoking. The memo itself echoed the counsel of public-relations experts who had been advising the tobacco industry since the 1950s—when the cancer-smoking link first began appearing in the news. They urged companies to obscure the known risks by generating “Controversy! Contradiction!” and introducing “Other Factors! Unknowns!” in the words of one top public-relations specialist. In a grim twist, the critics of electronic cigarettes have now become the merchants of doubt, contradicting the science and stirring up controversy. The Centers for Disease Control, for example, have continually sown seeds of doubt. “Guilty until proven innocent,” is how then-director Dr. Thomas Frieden, spoke of e-cigarettes in 2013. Healthy skepticism is one thing, but Frieden persisted in warning that vaping was a “gateway” to teen smoking, even though his own agency’s data did not support his claim.  State departments of health regularly dispensed misinformation, from doom-laden implications for teens, to exaggerated risks to adults, to denial of evidence that e-cigarettes help smokers quit. The Tennessee Medical Association and the University of Rochester Medical Center maintained that e-cigarettes are no safer than smoking. The prestigious medical journal, Lancet, editorialized, “No solid evidence base underpins the marketing claims that e-cigarettes are healthier than cigarettes or that they can support quitting.” A Harvard pediatrician called vaping “bioterrorism.” The American Heart Association dubs the relative safety of vaping an “unfounded belief,” with e-cigarettes having “many downsides. Few potential upsides.” In an interview with The New York Times, Dr. Albert Rizzo, chief medical officer for the American Lung Association, the journalist reported that he “disputed the perception that e-cigarettes are a safer alternative, and pointed to the lack of information about what chemicals they contain and the paucity of research about the effects of vaping.” The stock warning that “vaping is not safe” is technically true, but clearly intended to mislead. Absolute safety is not the point. Relative safety compared to the grave dangers of smoking is what smokers and their loved ones need to know.
Just the Facts
To that end, it is worth addressing some of the most common misconceptions about e-cigarettes, their risks, and their benefits. To start, some over-cautious health officials claim that e-cigarettes are not safer than combustible cigarettes and that we don’t know what is in them. This is blatantly false. A 2018 report from the National Academy of Sciences, Engineering and Medicine concluded, “There is conclusive evidence that completely substituting e-cigarettes for combustible tobacco cigarettes reduces users’ exposure to numerous toxicants and carcinogens present in combustible tobacco cigarettes” [italics in the original]. The Royal College of Physicians found that “although it is not possible to precisely quantify the long-term health risks associated with e-cigarettes, the available data suggest that they are unlikely to exceed 5% of those associated with smoked tobacco products, and may well be substantially lower than this figure.” The College’s estimate is based on risk analysis derived from measures of exposure to toxins in the saliva, blood, and urine of vapers compared to smokers and non-smokers and on the toxicology of e-cigarette aerosol compared to cigarette smoke. The latter contains roughly 7,000 chemicals, including 70 known human carcinogens, carbon monoxide, nitrogen oxides, and other gaseous constituents. E-cigarette aerosol also contains toxins and carcinogens, but they are far fewer in number than those found in cigarette smoke, and they are present at much lower levels. One particularly stubborn claim is that e-cigarettes emit dangerous levels of formaldehyde. Its provenance is a 2015 report in the New England Journal of Medicine entitled “Hidden Formaldehyde in E-Cigarette Aerosols” claiming that vapers faced a cancer risk from formaldehyde exposure that is five to 15 times higher than that of smokers. This alarming finding, which made headlines worldwide, was an artifact of researchers testing a vaping device at an unrealistically high voltage setting. Although overheating e-liquid does produce high levels of formaldehyde, no person could ever force himself to inhale such acrid vapor. When those same researchers tested the device at a realistic voltage level, no formaldehyde was detected (however, other analyses have detected formaldehyde in e-cigarette aerosol at very low levels). This caveat did not make it into the worldwide media coverage of the study. A further misconception is that we don’t know the effects of vaping. Multiple studies with follow-up periods ranging from one month to three years have documented health benefits after switching from smoking to vaping ranging from lower blood pressure, reduced abnormalities in cellular lining of blood vessels, lowered vascular stiffness, and improved lung function in smokers with chronic obstructive pulmonary disease and asthma. Whether long-term health problems will develop after years of consuming e-liquid constituents—propylene glycol, glycerin, and flavorings—remains to be seen. Epidemiologists must follow vapers for years to come (knowing that the interpretation of long term outcomes will be complicated by the fact that most vapers have first been smokers), and manufacturers must employ continuous surveillance to maintain and improve quality control and purge potentially toxic residues from flavorings. Still, the difference in toxic emissions between conventional, tobacco-combusting cigarettes and electronic ones will almost certainly save an extraordinary number of lives. The health benefits of vaping do not make compelling headlines. More attention grabbing is research purporting to show that vaping causes harm. One false scare that has become a staple of anti-vaping “public education” is the threat of “popcorn lung” (formally, bronchiolitis obliterans), which is caused by inhaling a chemical called diacetyl. The rare condition is called popcorn lung because it has been known to develop in workers in microwave-popcorn factories who were exposed to massive doses of diacetyl. When researchers tested samples of e-liquids, the aerosol produced in almost half surpassed strict federally defined occupational-safety limits. In response, many vaping manufacturers removed diacetyl as a precaution, though not a single documented case of popcorn lung has been detected in millions of vapers worldwide. What’s more, the exposure to diacetyl from cigarette smoking is one hundred times higher than from vaping, and popcorn lung is not a condition known to afflict smokers. The health press is also replete with warnings of vaping-induced heart attacks and acute or chronic pulmonary conditions. Yet a look at the research behind the headlines often reveals striking problems in study design. This February, the Journal of the American Heart Association retracted an article purporting to show that vaping increased the risk of heart attacks—but not until other scientists argued strenuously with the journal editors to invalidate it. Consider a recent report in the American Journal of Preventive Medicine in which researchers analyzed government data in order to determine a possible association between vaping and chronic lung disease. The data comprised a cohort of smokers and vapers who were surveyed at three intervals over a four-year period. At each interval, subjects were asked whether they had been diagnosed with chronic pulmonary disease. Many of the vapers who did not report disease at the first interval went on to report it at subsequently, leading the authors to conclude that e-cigarettes constituted a risk for chronic obstructive pulmonary disease, bronchitis, and asthma. What makes this inference dubious, however, is the fact that chronic lung conditions take at least two decades to manifest, far longer than four years covered by the surveys. Confounding results further is the fact that over 99% of the subjects studied were former smokers or dual users (that is, they vaped and smoked simultaneously), strongly suggesting that they had chronic lung problems long before the study began, even if those conditions were not formally diagnosed. Even those who switch completely to e-cigarettes remain at elevated risk for lung disease for years to come because of the damage inflicted by years of smoking. To be fair, researchers themselves will often acknowledge the limits of their studies—and sometimes those qualifications are substantial enough to invalidate the investigations outright—but those acknowledgements don’t reliably make it into the media’s coverage. Furthermore, despite claims to the contrary, second-hand vapor is not dangerous. E-cigarette vapor is not comparable to environmental tobacco smoke. The latter can linger for hours while environmental e-cigarette aerosol is very dispersive, evaporating in less than two minutes and practically undetectable at five feet from the exhalation. This means that bystanders in typical home or restaurant environments are exposed to extremely small dose of pollutants and for much less time than those exposed to tobacco smoke. Some of the most panicked claims are those about youth use—the primary source of anxiety for anti-vaping crusaders. They claim that vaping is a “gateway” to smoking. This claim is tricky, in part because the term “gateway” is deployed inconsistently. It may refer to a sequence (action B came after action A); other times it refers to a predictive, causal statement (a person engaged in action B because he first engaged in A). Causality is very hard to prove; after all, it is possible that action B would have happened anyway. For example, a teen with a high tendency toward risk-taking behavior, such as alcohol and marijuana use, which makes him more likely to experiment will be prone to try or use both e-cigarettes and cigarettes independently of each other. Such a teen, therefore, might well have smoked, whether or not he first vaped, as data indicate is typically the case. Reassuringly, though, there is little evidence that adolescents who vape move on to smoking. In fact, youth smoking rates, which have been declining for decades, dropped more steeply in the years that youth vaping increased most, between 2013 and 2019, reaching a record low in 2019 of 5.8%. This pattern, and other analyses, suggests that vaping serves as more of an off-ramp from smoking or as an alternative for adolescents who would have otherwise initiated smoking. In addition, most young users are infrequent users or experimenters; the minority that consumes frequently (defined as 20 to 30 days in the past month) largely comprises teens who have already used tobacco. In 2018, only 1% of adolescents who never used tobacco vaped frequently. Granted, that tiny percentage will likely increase if the numbers of frequent pod-system users grow. Nonetheless, anxieties regarding the “re-normalization” of youthful smoking are unfounded. The charge that nicotine leads to brain damage in youth is perhaps the most extravagant. California’s standard curriculum on vaping for high-school students, for instance, refers to nicotine as “brain poison for youth.” Michael Bloomberg, a fierce detractor of e-cigarettes, warns that adolescent vapers risk IQ losses of 10 to 15 points “for the rest of [their] entire life.” Frances Leslie, a scientist at the University of California at Irvine, described teen vapers as “guinea pigs for the effects of nicotine on the brain.” More soberly, the Surgeon General’s office warns, “Youth and young adults are also uniquely at risk for long-term, long-lasting effects of exposing their developing brains to nicotine.” It is true that aspects of brain development persist into the early 20s, but there are no compelling data at this time showing cognitive decrement in adolescents who have taken up vaping. Nor are there signs of brain impairment in many earlier generations of adult smokers who consumed large quantities nicotine starting in their youth. The claims of nicotine-induced harm are based, in part, on studies of the brains of adolescent rats exposed to nicotine. Their brains do show neuronal alterations, but what those changes mean for human teen brains, however, is far from clear. The claims also rely on examinations of cognitive function in young smokers. Regardless of age, however, smokers expose themselves to many other chemicals in addition to nicotine. Furthermore, the results of these cross-sectional studies may be biased by the established connection between teen smoking and pre-existing problems that are correlated with deficits in cognitive performance, such as conduct disorder, mental illness, and high school drop-out rates. What’s more, additional evidence suggests little correlation between IQ and smoking status. What we do know is that e-cigarettes help smokers quit (despite recent doubts voiced by Surgeon General.) As a recent article in Science roundly states, “Evidence from multiple strong observational studies and randomized trials suggests that vaping nicotine is more appealing and more effective than [patches, gum, lozenges] at displacing smoking.” One of those trials was published in the New England Journal of Medicine. Researchers followed almost 900 smokers and found that e-cigarettes are almost twice as effective as nicotine replacement therapies at helping smokers quit for one year (the duration of the follow-up period). Paradoxically, the defamation of vaping has proceeded apace as new studies show again and again that e-cigarettes are safer than combustible products and more effective than standard methods in helping smokers quit. Over time, the steady drip of misleading information became a torrent that turned the tide of public opinion. A survey conducted by the National Cancer Institute found that in 2012, 39% of respondents believed that e-cigarettes were “safer” or “much safer” than smoking. The next year, 43% held that belief. That ascendant trajectory, unfortunately, started to turn down in 2014, eventually declining to 17% in 2018. A 2019 Reuters poll found that 63% of Americans disagreed with the statement that “vaping is healthier than traditional cigarettes,” a 16 percentage point increase from the spring of 2016. Currently, 72% of voters support a ban on fruit and candy that vaping should be illegal for adults. Surveying the assault on truth, Michael Siegel, a physician, former CDC researcher, and professor of public health at Boston University, concluded in spring 2019 that the tobacco control movement had committed “public-health malpractice by misrepresenting the health effects of vaping.” The public has been swept up in an “availability cascade,” a term coined by economist Timur Kuran and regulatory expert Cass Sunstein to denote “a self-reinforcing process of collective belief formation.” Cascades gain unstoppable momentum as the public hears the same message repeatedly and believes it is true. In the case of vaping, tobacco-control activists have acted as “availability entrepreneurs,” as Kuran and Sunstein would call them, manipulating the media to unleash influential availability cascades. Eventually, enshrined dogma surrounding vaping precluded authorities from thoughtful analysis of risks. The most pressing of question—how should we reconcile one additional underage vaper against one middle-aged adult quitting smoking—gave way to the settled assumption that whatever known benefits accrued to smokers were outweighed by prospective harms to youth. The conversation ended before it began.
The End of Vaping?
In fall 2018, the campaign against e-cigarettes intensified. A new survey from the CDC showed a 78% increase from the prior year in the number of youth who vaped at least once in the past month, from 11.7% to 20.8%. Immediately, the FDA called teen vaping an “epidemic.” The spike was due to the immense popularity of JUUL in high schools where students can afford the $50.00 starter kit, and its knock-offs. Easily hidden and camouflaged, the device became so popular that roughly half of seniors in some schools were said to be “juuling.” The seeming ubiquity of the device spurred three New York City mothers to form Parents Against Vaping E-Cigarettes, now a fixture at state houses and in Congress, where they lobby against vaping, which they describe as “the most serious adolescent public-health crisis our country has faced in decades.” Some concerns are valid. For one, JUUL’s early marketing appeared to have crossed a line. An independent analysis of its advertising found that the company had used “patently youth oriented” imagery for its first six months, from June to December 2015, and subsequently paid social-media influencers known to be popular with teens to hype the product. Since then, the company has employed tight restrictions on sales to minors and against straw purchasing, wherein legal purchasers buy on behalf of the under-aged, and last year, removed all flavors except for menthol and tobacco. In addition, JUUL’s product may well be able to compete with cigarettes in terms of nicotine delivery. Its pods contain a higher level of nicotine than many other vaping products, and a particular manufacturing process enables nicotine to be rapidly absorbed into the blood through the lungs and into the brain. This is a necessary feature of e-cigarettes, not a bug; when it comes to smokers, the goal is to create an experience that is as satisfying with many fewer toxicants. But this efficient nicotine delivery enhances the risk of dependence and addiction in those new to nicotine; JUUL aerosol is less irritating than cigarette smoke, and the smoother “throat hit” makes it possible for teens unaccustomed to cigarettes to consume high nicotine levels. Consequently, JUUL has drawn intense scrutiny. The House Committee on Oversight and Reform is investigating the company’s role in the “youth nicotine addiction epidemic.” Plaintiffs ranging from outraged parents to state attorneys general have filed lawsuits alleging that JUUL, now dubbed Big Vape, purposefully marketed its products to underage users. In the meantime, illegal JUUL knock-offs (which teens nonetheless refer to as “JUUL”) are rampant in convenience stores and yet the FDA has done little to intercept them. Against this fraught backdrop, several events of the last two years turbo-charged the anti-vaping cause. Most urgent was an outbreak of lung illness. The first case appeared in April 2019 and the number of new cases increased sharply between early June and early September. As of December, 2,291 people had been sickened and 48 died. By late summer, health officials had traced the vast majority of these tragedies to vaping contaminated cannabis products, finding that the culprit was the additive Vitamin E acetate. Nevertheless, many health officials persistently and wrongly attributed the illness to the vaping of retail nicotine, sending concerns about e-cigarettes to stratospheric levels. Notably, it took the CDC until January 2020, lagging months beyond the FDA, to signal definitively that nicotine vaping was not a risk for acute lung disease. “It is always hard to prove intent,” concedes Clive Bates, a former director of Action on Smoking and Health, “but there is every sign of a deliberate effort to keep doubt alive that nicotine e-liquids could be implicated.” Lamentably, a poll taken earlier this year reveals that two-thirds still view e-cigarettes as the cause of the lung disease, up from 58% five months earlier. In the midst of the lung-injury crisis caused by contaminated THC products, the CDC released 2019 data on teen vaping. Among high-school students, 27.5% reported vaping at least one day in the previous month—up from 20.8% in 2018. Shortly thereafter, a second government survey found that 11.7% of high-school seniors vaped at least 20 days per month (no prior year figures were reported). The findings prompted the Trump administration to announce a ban on all e-cigarette flavors except tobacco in order to make vaping less appealing to teens. (Notably, while teens enjoy flavors, they are not lured into vaping by them, contrary to this popular assumption. The top two reasons teens vape, according to a CDC survey, are “curiosity” and “friend or family use them.”)  Michigan, Rhode Island, Washington, Oregon, and New York, have banned all fruit and candy flavors or have taken steps to do so. Walmart, Kroger’s, and Walgreen’s announced plans to stop selling e-cigarettes altogether. In early February, the FDA announced it would begin banning fruit and candy flavors in non-disposable pod-based devices. Later that month, the House passed a radical bill banning sales of all flavors except tobacco in all devices. The White House opposed it. Restrictions on flavors is a serious threat to vapers. Surveys routinely report that vapers strongly prefer fruit flavors over tobacco flavor. Their bias makes sense according to classic behavioral psychology: to prevent relapse, a smoker trying to quit should dissociate from the taste of smoking, and would be likely to resume cigarettes if their preferred alternative flavors are no longer available. A 2018 preference survey of 70,000 adult vapers found that fruit and dessert flavors are the most popular by far, with only a minority using tobacco flavors. Prohibition has had predictable consequences. Anecdotes of smokers going back to cigarettes or patronizing black markets that sell vapes of dubious quality are accumulating and vapers report they will “find a way” to get flavors. Poison-control centers should brace for do-it-yourselfers trying to dilute concentrated nicotine and mix it with flavors in their kitchens. Perhaps our current predicament was inevitable, but the presence of a streamlined and affordable statutory pathway to FDA approval of vaping products might have buffered the onslaught to some degree. As of today, more than a decade after the Tobacco Control Act was passed in 2009 allowing for the regulation of tobacco products, no vaping products have undergone the complete formal approval process, though all commercial sellers have been registered with the FDA and the ingredients of e-liquids filed with the agency. Lack of government approval makes the public nervous, so when a product is in a state of regulatory limbo, it is easier for alarmist claims to gain traction.
From Promising Innovation to Public-Health Menace
In their campaigns against e-cigarettes, many health agencies and advocates breached two fundamental tenets of public-health practice: dispassionate and nuanced analysis of risk and honest communication about that risk to the public. Opponents of vaping defined the problem solely as a matter of teen vaping while abdicating their responsibility to address the problem of adult smoking. (They were reluctant to acknowledge any benefit to low-income teen smokers, if they did not refuse to address the issue altogether.) Youth should not vape, nor should adults smoke. Both imperatives need to be taken into account and trade-offs made. Unfortunately, a vast swath of the tobacco-control community seemed to forget that the purview of public health is the nation’s entire population of vulnerable people, not just youth, and particularly groups that smoke at disproportionately high rates, including people suffering mental illness, working-class men and women, Native Americans, veterans, and lesbian, gay, and bisexual adults. The ultimate loss of perspective, jarring in its significance to anyone who looks beyond the vaping tumult, is that combustible cigarettes remain untouched and easier to purchase while a safer alternative is under siege. Truth telling has been a bloody casualty in the vaping wars. “Great is the power of steady misrepresentation,” Charles Darwin wrote in The Origin of Species, “but the history of science shows that fortunately this power does not long endure.” In this case, Darwin’s outlook may be too optimistic. Although innovation has always had its enemies, it seems safe to say that this is a unique episode in the history of modern public health, when otherwise-respected institutions, doctors, and public professionals relentlessly inculcated doubt against a product (e-cigarettes) and a practice (vaping) by disseminating half-truths, non-sequiturs, and brazen falsehoods. Even in the midst of the high-profile, celebrity-studded anti-vaccination crusade, the public could at least turn to trusted sources for sensible and objective information and advice. These transgressions will have repercussions. Institutions entrusted to inform and guide the public may suffer a serious loss of faith, disaffecting youth as much, if not more, than adults. Tobacco controllers, like tobacco companies before them, obscured, rather than advanced, health literacy. In the more-immediate policy sphere, bans on flavors and restricted access to e-cigarettes will cause many to revert to smoking or to patronize illicit markets. With policymakers and politicians so woefully misinformed about the virtues and realistic risks of vaping, it is no surprise if they fail to appreciate the magnitude of the dangers that their restrictive policies pose. “If we lose e-cigarettes, I think we will have blown the single biggest public health opportunity we’ve ever had,” says David Abrams of the NYU College of Global Public Health. The e-cigarette story is a dire chapter in the sociology of public-health science. In the future, however, it could prove to be an instructive one as well. If there are any grounds for optimism in the long-run, they come from abroad. Public health authorities in England, Canada, and New Zealand endorse and promote vaping as a harm-reduction strategy for smokers. As these nations save smokers’ lives—and as illicit vaping markets take root here—American policymakers and the public will be forced to notice. They will need to adjust their risk-benefit calculus and their policies accordingly. They will need to acknowledge, too, that many of the same activists who fought heroically against the deceptions of Big Tobacco, were the same ones who thwarted a nascent health revolution, slanting science to fulfill their own mission. I wish to thank the following experts: David Abrams, Scott Ballin, Clive Bates, Annie Kleykamp, Jacob Grier, Brad Rodu, Roberto Sussman, Kenneth Warner, Mark Slis, David Sweanor, Alan Viard
 The number of adult vapers vary, see
a. From Q2 earnings call – available here: http://investor.altria.com/Cache/1001255076.PDF?O=PDF&T=&Y=&D=&FID=1001255076&iid=4087349 Data as of June 2019 (moving average)
i. Total adult vapers: 13.8MM ii. Vapers who do not smoke cigarettes: 7.1MM iii. (Trends in slide 17 at the link)
b. From 2018 NHIS (National Health Interview Survey) https://www.cdc.gov/mmwr/volumes/66/wr/mm665152a7.htm; https://www.cdc.gov/mmwr/volumes/65/wr/mm6542a7.htm?s_cid=mm6542a7_w
i. Total vapers: 8.1MM ii. Vapers who do not smoke cigarettes: 4.7MM
c. Annals of Internal Medicine – 10/18 (2016 data): https://annals.org/aim/article-abstract/2698112/prevalence-distribution-e-cigarette-use-among-u-s-adults-behavioral
i. Total vapers: 10.8MM
 Michael Bloomberg pledged $160 million to the cause. Former Bloomberg who called vaping “an urgent health crisis,” asserting that there is “no evidence what so ever that it does anything to help you stop smoking…in fact, most people that vape have never smoked before.” https://www.youtube.com/watch?v=Gx2p-NraM2s Bloomberg who called vaping “an urgent health crisis,” asserting that there is “no evidence what so ever that it does anything to help you stop smoking…in fact, most people that vape have never smoked before.”  Citing personal e-mail from Roberto Sussman PhD, Universidad Nacional Autónoma de México, Dec. 23, 2019, “In rough terms: each cigarette delivers 1-2 mg of nicotine (80% of the nicotine in a cigarette is released to the environment by side stream emissions). “Each 5% JUUL pod contains approximately 0.7mL with 5% nicotine by weight (approx. 40 mg per pod based upon 59 mg/mL) at the time of manufacture. Each 3% JUUL pod is designed to contain approximately 0.7mL with 3% nicotine by weight (approx. 23 mg per pod based upon 35 mg/mL) at time of manufacture” at https://www.JUUL.com/resources/JUUL-Pods-Cost-and-Pricing-Pods-Prices-for-All-Flavors]. “So, using these weight estimates the nicotine intake of 5%, 3% JUUL pods would be respectively equivalent to 20-40 or 15-25 cigarettes. However, not all nicotine in the e-liquid is aerosolized, see http://dx.doi.org/10.1136/tobaccocontrol-2018-054565 A 5% JUUL delivers about 0.83 mg of nicotine in 10 puffs, while in a typical cigarette 1-2 mg of nicotine are smoked in 10-15 puffs. This means that each JUUL puff is roughly equivalent or slightly less than a cigarette puff.”  Nicotine does not cause cancer, see Public Health Consequences of E-Cigarettes, National Academies of Sciences, Engineering, and Medicine; Health and Medicine Division; Board on Population Health and Public Health Practice. Eaton DL, Kwan LY, Stratton K, editors, Washington (DC): National Academies Press (US); 2018 Jan 23. 4, Nicotine at https://www.ncbi.nlm.nih.gov/books/NBK507191/ and Does nicotine cause cancer? European Code Against Cancer, International Agency for Research on Cancer, World Health Organization, at https://cancer-code-europe.iarc.fr/index.php/en/ecac-12-ways/tobacco/199-nicotine-cause-cancer. However, over half think it does: https://hints.cancer.gov/view-questions-topics/question-details.aspx?nq=1&qid=1514  “The promotion of electronic cigarettes and other innovative tobacco products is much more likely to be beneficial in an environment where the appeal, accessibility, promotion, and use of cigarettes are being rapidly reduced,” said the report; click associated link and then word search.  Richard Kluger, Ashes to Ashes: America’s Hundred-year Cigarette War, the Public Health, and the Unabashed Triumph of Philip Morris, Knopf, 1996 p. 324.  Frieden had told CNN in 2013 that e-cigarettes must be treated as “guilty until proven innocent,” cited in Fairchild, AL, et al., E-Cigarettes and the harm reduction continuum, New England Journal Medicine, 378 (3) 2018:216-218 at https://www.nejm.org/doi/full/10.1056/NEJMp1711991. When pressed, Frieden would concede that vaping was safer than smoking, but rarely raised it spontaneously, see Frieden, T, CDC telebriefing: new Vital Signs report — why is youth e-cigarette advertising harmful for youth? Atlanta: Centers for Disease Control and Prevention, Jan 5, 2016.  For a powerful critique of CDC obfuscation see https://www.psandman.com/col/e-cigs.htm and for explanation of how CDC’s reported 2013 to 2014 spike was exaggerated because the agency changed the survey design of the National Youth Tobacco Survey, see https://rodutobaccotruth.blogspot.com/2015/10/the-cdc-buries-lead-teen-e-cigarette.html  The California Department of Health’s campaign in 2015, Still Blowing Smoke, alerted the public the danger of nicotine residue on walls and table tops, this is a matter presented in the ads as a threat. In fact, concentrations of ambient nicotine emitted by e-cigarettes are well below biologically meaningful levels and are not a threat to bystanders, see here and here.  P 87 of full report obtainable here: https://www.rcplondon.ac.uk/projects/outputs/nicotine-without-smoke-tobacco-harm-reduction “Although it is not possible to precisely quantify the long-term health risks associated with e-cigarettes, the available data suggest that they are unlikely to exceed 5% of those associated with smoked tobacco products, and may well be substantially lower than this figure”. (Section 5.5 page 87); also see Nutt, DJ , et al. Estimating the harms of nicotine-containing products using the MCDA approach, European Addiction Research, 2014, 20, 218–25 at https://doi.org/10.1159/000360220  See Shahab, L, et al. Nicotine, Carcinogen, and Toxin Exposure in Long-Term E-Cigarette and Nicotine Replacement Therapy Users: A cross-sectional study. Annals of Internal Medicine, 2017, 166:390–400 at https://annals.org/aim/article-abstract/2599869/nicotine-carcinogen-toxin-exposure-long-term-e-cigarette-nicotine-replacement and Goniewicz, ML, et al., Exposure to nicotine and selected toxicants in cigarette smokers who switched to electronic cigarettes: A longitudinal within-subjects observational study, Nicotine Tob Res., 2017, 19(2): 160–167 at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5234360/, see Goniewicz, ML, et al., Levels of selected carcinogens and toxicants in vapour from electronic cigarettes, Tobacco Control, 2014, 23: 133-139 at https://tobaccocontrol.bmj.com/content/23/2/133 and Margham, J, et al., Chemical composition of aerosol from an e-cigarette: A quantitative comparison with cigarette smoke, Chemical Research in Toxicology, 2016, 29, 10, 1662-1678 at https://pubs.acs.org/doi/full/10.1021/acs.chemrestox.6b00188  Polosa, R, et al., The effect of e-cigarette aerosol emissions on respiratory health: a narrative review, Expert Review of Respiratory Medicine, 2019 Jul, 899-915 at https://www.tandfonline.com/doi/full/10.1080/17476348.2019.1649146; Pelosa, R, et al., Evidence for harm reduction in COPD smokers who switch to e-cigs, Respiratory Research, 2016, 17(1): 166; Polosa, R, et al., Health effects in COPD smokers who switch to electronic cigarettes: a retrospective-prospective 3-year follow-up, Int J Chron Obstruct Pulmon Dis, 2018 Aug 22;13:2533–2542 at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6113943/ (note that the 3 year follow up found that e-cig users with COPD had a significant reduction in COPD exacerbations, by about 40%. Also, in the same study, a substantial number of COPD patients in the E-cig study group improved in term of disease severity. This manifests in medication use reductions as well as fewer hospitalizations) Polosa, R, et al., Persisting long term benefits of smoking abstinence and reduction in asthmatic smokers who have switched to electronic cigarettes, Discovery Medicine, 2016 Feb, 21(114): 99–108 at https://www.ncbi.nlm.nih.gov/pubmed/27011045.  https://twitter.com/FarsalinosK/status/1197683057077166080; https://www.clivebates.com/more-on-new-england-journal-of-medicine-fake-formaldehyde-scandal/; Farsalinos, KE, et al., Evaluation of electronic cigarette liquids and aerosol for the presence of selected inhalation toxins, Nic Tob Res. 2015; 17(2):169-174 at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4892705/  Bell, K and Keane, HD, All gates lead to smoking: the ‘gateway theory’, e-cigarettes and the remaking of nicotine, Soc Sci Med, 2014 Oct, 119: 45-52 at https://www.ncbi.nlm.nih.gov/pubmed/25150650  Levy, DT, et al., Examining the relationship of vaping to smoking initiation among US youth and young adults: a reality check, Tobacco Control, 2019, 28 (6) 629-635 at https://tobaccocontrol.bmj.com/content/28/6/629  See more extensive commentary by Brad Rodu in comment section of Berry, KM, et al., Association of electronic cigarette use with subsequent initiation of tobacco cigarettes in US youths, JAMA Network Open, 2019, 2(2): e187794 at https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2723425. Also note: The benefits for a gateway out case rests on the accelerating decline in National Youth Tobacco Survey (by CDC) and 12th Grade smoking in the e-cig era (Monitoring the Future survey from NIDA) and time series analysis [Examining the relationship of vaping to smoking initiation among US youth and young adults: a reality check]; the research showing teens actually say use the products for smoking cessation and harm reduction [PATH Data: Harm reduction is teens’ top reason for using e-cigarettes]; the data showing that reductions in youth access to e-cigarettes tended to raise youth smoking rates [How does electronic cigarette access affect adolescent smoking?][The influence of electronic cigarette age purchasing restrictions on adolescent tobacco and marijuana use.]; and the fact that frequent vaping is concentrated in current or former teen smokers [Collins, LK, et al., Frequency of youth e-cigarette, tobacco, and poly-use in the United States, 2015: Update to Villanti et al., Frequency of youth e-cigarette and tobacco use patterns in the United States: Measurement precision is critical to inform public health, Nicotine Tob Res, 2017, 19 (10), at https://academic.oup.com/ntr/article/19/10/1253/3748287] – in other words, whatever they are doing represents a substantial modification of their smoking behavior.  Note the comment made in 2104 by National Institute on Drug Abuse director, Dr. Nora Volkow, to the Washington Post: “Nicotine does not interfere with cognitive ability. So if you are an adolescent and you are smoking marijuana and going to school, it’s going to interfere with your capacity to learn. So what is worse, as an adolescent right now? To have basically something that is jeopardizing your development educationally or to smoke a cigarette that, when you are 60 years of age, is going to lead to impaired pulmonary function and perhaps cancer… I would argue that you do not want to mess with your cognitive capacity, that that is a very large price to pay.” See https://www.washingtonpost.com/opinions/ruth-marcus-national-institute-on-drug-abuse-chief-attacks-myths-of-pot-smoking/2014/06/24/12010d84-fbd9-11e3-8176-f2c941cf35f1_story.html; Other studies shed doubt on a connection between nicotine exposure and cognitive decrement, see: Wennerstad, K, et al., Associations between IQ and cigarette smoking among Swedish male twins, Social Science and Medicine, Nov 20, 2009, at https://www.gwern.net/docs/iq/2010-wennerstad.pdf This shows that the (inverse) IQ–smoking association disappeared after adjustments for shared environment and genetics; see Corley, J, et al., Smoking, childhood IQ and cognitive function in old age, Journal of Psychosomatic Research, 2012, (Table 2) https://www.research.ed.ac.uk/portal/files/16310520/Corley_2012_Smoking_childhood_IQ_and_cognitive_function.pdf; also see Deary, IJ, et al., Regional cerebral glucose metabolism in akinetic catatonia and after remission, J Neurol Neurosurg Psychiatry 2003, 74: 1003–1007 at https://jnnp.bmj.com/content/jnnp/74/7/1006.full. Deary, IJ, et al. found that current smokers, but not ex-smokers, had lower IQ scores at age 80 (after adjusting for childhood IQ) when compared with lifelong never-smokers. Showing that past smoking was not associated with significantly poorer performance than never smokers in any cognitive domain  Additional dubious information from Office of SG at https://e-cigarettes.surgeongeneral.gov/knowtherisks.html  JUUL uses nicotine salts not freebase. The other novelty in JUUL is the strength of the liquid and use of benzoic acid to create a nicotine salt. This changes how and where the nicotine is delivered in the respiratory tract—more of it goes to the lung where it travels quickly to the brain. This gives it comparable pharmacokinetics (the dynamics of a drug within the body) to cigarettes. However, it can do this with much less liquid and a much smaller battery because there isn’t so much liquid to aerosolize. Not only did nicotine salts enable much higher nicotine levels by lowering the pH to make it palatable but, in vapor products, it also increased absorption rates thus transferred to the body via the lungs both faster and more easily and also crossed the blood-brain barrier more readily. As JUUL discovered, in vapor products it turns out it is the salt form of nicotine that gives that one-two punch: a smoother hit combined with more rapid nicotine delivery. See https://www.kaisvirginvapor.com/pages/nicotine-salts-a-vapers-guide  Hajek, P, et al., Nicotine delivery and users’ reactions to Juul compared with cigarettes and other e‐cigarette products, Addiction, first published Jan 29, 2020 at https://onlinelibrary.wiley.com/doi/full/10.1111/add.14936  Gartner, C. et al., Miscommunication about the causes of the US outbreak of lung diseases in vapers by public health authorities and the media, Drug and Alcohol Review, Jan 2020 at https://onlinelibrary.wiley.com/doi/full/10.1111/dar.13024  Relevant text from https://www.cdc.gov/mmwr/volumes/68/ss/ss6812a1.htm?s_cid=ss6812a1_w text: Among middle and high school students who ever tried using e-cigarettes, the most common reasons for e-cigarette use were “I was curious about them” (55.3%), “friend or family member used them” (30.8%), “they are available in flavors, such as mint, candy, fruit or chocolate” (22.4%), and “I can use them to do tricks” (21.2%) (Table 5). “I was curious about them” was the most commonly reported reason among current exclusive e-cigarette users (56.1%) and students who currently used both e-cigarettes and at least one other tobacco product (38.4%) (Table 6).  More detail from the linked study: If their preferred flavor or all the non-tobacco flavors were banned, very few participants anticipated that they would stop using e-cigarettes or use e-cigarettes less, but about 50% reported they would ‘find a way to buy my preferred flavor or ‘add flavoring agents myself’ (Table 4).’ A total of 36 (9.7%) reported that ‘I would return to smoking traditional tobacco cigarettes’, if all non-tobacco flavors were banned.’ from Du, P, et. al., Changes in flavor preference in a cohort of long-term electronic cigarette users, Annals of the American Thoracic Society, Jan 2020 at https://www.atsjournals.org/doi/pdf/10.1513/AnnalsATS.201906-472OC