A new study, based on a survey of about 7,700 Juul users, found that nearly half had quit smoking within three months of buying a starter kit, while the rest had reduced their cigarette consumption by an average of 52 percent. The survey results, reported in the Journal of Pulmonary and Respiratory Medicine, provide further evidence that e-cigarettes help smokers dramatically reduce their exposure to the toxins and carcinogens produced by tobacco combustion.

The survey, commissioned by Juul Labs and conducted by the Centre for Substance Use Research, started with 9,272 smokers who had bought starter kits online or from brick-and-mortar stores, of whom 7,721 responded to questions about their past-month smoking prior to the purchase and three months later. Forty-seven percent reported no smoking at all in the month before the follow-up. Among those who were still smoking, the number of cigarettes consumed during the previous month fell, on average, from 341 to 165, or from about 11 to about five a day.

E-cigarette skeptics frequently warn that people who use these products may continue to smoke even after they take up vaping, and these data confirm that dual use is common. But even if dual users do not eventually stop smoking completely, a 52 percent reduction in cigarette consumption is nothing to sneeze at. Another recent study found that smokers who switched entirely to vaping saw reductions in biomarkers of exposure to hazardous substances as big as people who stopped smoking without using e-cigarettes. Getting halfway there surely represents a significant improvement.

The researchers take a stab at translating these findings into estimates of Juul's population-wide impact on cigarette consumption. If 20 percent of smokers use Juul, for example, that would represent 84 million fewer cigarettes smoked per month.

The sample in this study is self-selected, so you would not expect to see the same results in a group of randomly selected smokers. People who buy Juul starter kits are probably especially motivated to quit (or cut back) and especially likely to find that vaping is an adequate substitute for smoking. But a randomized study reported in January found that e-cigarettes were almost twice as effective in achieving smoking cessation as other forms of nicotine replacement.

In the real world, smokers will tend to gravitate toward the cessation methods that work best for them, so it's important that they have a wide range of options. The Food and Drug Administration, which acknowledges the enormous harm-reducing potential of e-cigarettes, is nevertheless proceeding with a plan that will limit those options by restricting the availability of most e-liquid flavors.