Few studies have been carried out to assess directly the impact of e-cigarette use on smoking-related diseases including cardiovascular disease, lung disease and cancer.
Despite this lack of direct evidence, there is a general view that the risks associated with e-cigarette use, in terms of tobacco-related diseases, are likely to be far less than those associated with the use of combustible tobacco. This is likely due to the far lower levels of toxicants found in e-cigarette vapour.
Pharmacokinetics is the study of the rates of absorption, distribution, metabolism, and excretion of a drug/chemical in vivo. A regular combustible cigarette delivers a nicotine peak of 18-20 ng/ml in blood plasma shortly after smoking. One early study of e-cigarette usage by inexperienced e-cigarette users observed peak plasma nicotine values of 1-3 ng/ml whereas a later study of experienced e-cigarette users using higher output e-cigarettes showed peak plasma nicotine concentrations above 15ng/ml, demonstrating that similar levels of plasma nicotine to cigarette smoking can be achieved.
Few studies examining biomarkers of exposure (other than plasma nicotine) and of biological effect have been performed in subjects switching from conventional cigarettes to nicotine-containing e-cigarettes, although one study has concluded that blood-cell counts were not altered in smokers using e-cigarettes (whereas the counts increased when the smokers smoked tobacco cigarettes).
More commonly, clinical studies have examined the subjective effects of e-cigarette use (cravings, withdrawal symptoms or reinforcement) or user behaviour (dual use, cessation and so on). Abuse liability has also been assessed in smokers using procedures in which subjects were asked to choose between e-cigarettes, combustible cigarettes and monetary reward. Data from this study indicate a lower abuse liability than combustible cigarettes.