Efficacy of E-Cigarettes in Tobacco Cessation and Dual Use of ENDS and Cigarettes

"Among adults, reductions in cigarettes per day were observed in several of the clinical studies^83,84,86 and in 1 population-based study⁴ among those who did not quit. Reduction in cigarettes smoked per day could have benefit if it promotes subsequent cessation, as has been found with NRT,90 but this pattern has not yet been seen with e-cigarettes. In the cigarette reduction analyses presented in some of the studies, many participants were still smoking about half a pack cigarettes per day at the end of the study.
"Both duration (years of cigarette use) and intensity (cigarettes per day) determine the negative health effects of smoking.⁹¹ People who stop smoking at younger ages have lower age-adjusted mortality compared with those who continued to smoke later into adulthood.92 Findings for decreased smoking intensity have been less consistent, with some studies showing lower mortality with reduced daily cigarette consumption⁹³ and others not finding a significant overall survival benefit.⁹⁴ The 2014 report of the US Surgeon General concluded that 'reducing the number of cigarettes smoked per day is much less effective than quitting entirely for avoiding the risks of premature death from all smoking-related causes of death.'⁹⁵ Use of electronic cigarettes by cigarette smokers to cut down on the number of cigarettes smoked per day is likely to have much smaller beneficial effects on overall survival compared with quitting smoking completely."