Despite increasing evidence that vaping is safer than smoking, uncertainty surrounds the long-term effects of electronic cigarette use. Many in the tobacco control field have used the lack of data to speculate about these unknown risks. Here's a better way to deal with the uncertainty.
A growing body of evidence gathered over the last 15 years has shown that using an electronic cigarette ("vaping") is probably far safer than smoking and likely to help smokers quit their deadly habit forever. Certain segments of the public health establishment have reacted oddly to these results—they've ignored them and treated vaping as a serious threat. The American Heart Association, for example, has even called for e-cigarettes to be taxed and regulated as stringently as tobacco products are. 
Fortunately, this view doesn't seem to be as predominant as it once was; we're beginning to see more physicians, scientists, and public health organizations make statements based on the available science instead of what they think the evidence might show one day.
Consider this May 24 review article published in Prescriber: E-cigarettes: informing the conversation with patients by Anna Kate Barton. The author, a clinical research fellow at the University of Edinburgh in the UK, helpfully outlined the history, anatomy, and science of e-cigarettes with the aim of helping doctors more knowledgeably discuss vaping with their patients. Compared to the typical news report about vaping—"Vaping is not better than smoking, and it still causes long-term lung damage"—Barton's article illustrated how we should talk about scientific issues when the evidence surrounding them is evolving. Let's consider a few examples.
What does the current evidence say about vaping and smoking cessation? ACSH has previously reported that vaping very likely helps smokers quit cigarettes, and maybe even nicotine, for good. Citing some of the same literature we have, Barton reached a similar conclusion about smoking cessation. While acknowledging the limitations of these studies (discussed here), she explained:
Patients using e-cigarettes also often report greater satisfaction and greater reduction in smoking than those using nicotine patches, and e-cigarettes are regarded as the most popular form of smoking cessation aid with smokers wishing to quit. Current position statements and the existing evidence base advocate their combination with stop smoking counseling, the most effective smoking cessation tool.
This comes down to a concept known as “harm reduction.” Ideally, people would never take up smoking. But since they do, the goal should be to help them mitigate the risks when abstinence isn't feasible. More experts are beginning to embrace this approach in order to enhance smoking cessation campaigns, as Barton noted:
E-cigarettes as aids to smoking cessation are advocated by several organizations including Public Health England. This is based on the principle of risk-reduction – simply, e-cigarettes provide nicotine in a much safer form that traditional cigarettes. Although neither are entirely risk-free, e-cigarettes are generally accepted to confer less risk to both the user and passive smokers than traditional cigarettes.
Health risks of vaping
After contrasting the overall risk of vaping with smoking, Barton added that some preliminary studies have indeed associated e-cigarette use with various negative outcomes. For example, an onslaught of headlines in mid-2019 warned the public about an outbreak of “e-cigarette or vaping product use-associated lung injury” (EVALI). Under-reported at the time was the fact that the injury-causing devices were typically purchased illegally and contained THC or certain dangerous additives, which made them far more harmful than the nicotine-containing devices adult customers can legally purchase in licensed vape shops in the US and UK. Surveying the literature nearly two years later, we get a better sense of the problem:
Interestingly, 82% [of EVALI cases] reported use of THC-containing [vape] products. Vitamin E acetate is sometimes added as a condensing agent in e-liquid, particularly in those containing THC, and this has been associated with EVALI. As such, the CDC discourages use of THC-containing [vape products], particularly those sourced informally from family or friends.
The point, then, is that proper regulation and vigilance by individual users can minimize these types of injuries. The UK, where vaping has proven to be a similarly popular smoking cessation approach, “has not thus far experienced a similar epidemic of EVALI as the USA,” Barton added, though she mentioned two severe cases that apparently weren't related to THC or Vitamin E acetate.
About those long-term effects
Opponents of vaping often point to the dearth of research on its chronic health effects as a first line of criticism. This is a fair enough point, but I hasten to add that it cuts both ways. If we don't know the long-term effects of vaping, we don't know the long-term effects of vaping. “At present,” Barton observed in reference to chronic lung disease, “we can only reflect on potential consequences of 10–15 years of widespread e-cigarette use.”
But that's often not what tobacco control advocates do. “The long-term risks of exclusive use of e-cigarettes are not fully known,” The American Cancer Society claims, “but evidence is accumulating that e-cigarette use has negative effects on the cardiovascular system and lungs. Without immediate measures to stop epidemic use of these products, the long-term adverse health effects will increase.” Retired University of California, San Francisco tobacco researcher Stanton Glantz has even suggested that e-cig users would “be better off just smoking.”
The impulse to reject anything tobacco-related is understandable. But we have to stick with the data we have, which suggests vaping is far safer than smoking, and wait for the long-term results to come in. What we can't do is minimize the existing evidence while simultaneously making statements about the future. Uncertainty is acceptable when we don't have enough evidence, as Barton wrote:
It seems unlikely that e-cigarettes will be without pathological consequences within the human lung and elsewhere, though when we will be able to prove or disprove this is less clear … Regular monitoring of suspected adverse events arising from e-cigarettes … will aid recognition of new complications in [the] future, though it is unlikely we will appreciate the full picture of any long-term harms until well into this century.
 The FDA classifies e-cigarettes as tobacco products, but this designation makes little sense. According to Nicotine and Tobacco Research, "If all products containing nicotine derived from tobacco were labeled as 'tobacco products' internationally, then nicotine-replacement therapies would be classified as tobacco products, which they are clearly not."